Potassium-free Solution Research Articles

Oral and maxillofacial surgery in patients undergoing dialysis for advanced renal disease: report of five cases

BackgroundPerioperativemanagement of hemodialysis patients involves many difficulties. High mortality rate and circulatory or respiratory complications in these patients were reported. However, in such reports, there is no concrete information of perioperative management in hemodialysis patients to prevent surgical complications and successful outcomes.Case presentationWe retrospectively reviewed the cases of 5 hemodialysis patients who underwent oral surgery under general anesthesia between January 2005 and December 2017.Primary disease was oral squamous cell carcinoma (SCC) in 4 patients and mandibular ameloblastoma in 1 patient. Partial resection was performed in 2 cases, neck dissection in 1 case. Two cases underwent surgery including vascularized reconstruction. The patients were dialyzed the day before and after surgery for the control of fluid and electrolyte status. Patients received intraoperative and postoperative intravenous infusion of potassium-free solution at 20–40 mL/h. Erythropoiesis-stimulating agents (ESAs) were used on the day of hemodialysis during hospitalization. Nafamostat mesilate as an anticoagulant during hemodialysis were used from postoperative day (POD)1 to 7. From POD 1 to 10, cephalosporin as prophylactic antibiotics is adjusted to quarter from half the initial dose. The resuming time of oral intake was similar to that of other oral surgery patients without kidney disease. The daily intake limits of protein, salt and liquid were managed during hospitalization and no cases suffered from malnutrition. No cardiorespiratory complications occurred during the perioperative period. In a case of vascularized osteocutaneous scapular flap reconstruction, grafted scapular bone survived and scapular cutaneous flap necrotized. Necrotic tissue was debrided and split thickness skin was successfully used to cover the grafted scapular bone.ConclusionsPostoperative better result could be achieved if adequate perioperative management specific to hemodialysis patients is carried out. Vascularized flap reconstruction at oral and maxillofacial region in hemodialysis patients is beneficial treatment. Even if the first flap has wound complication secondary flap reconstruction is success and aesthetically better results could be achieved by the strict wound management and debridement.

Abstract 90: Inimitable Ouabain: The Endogenous Circulating Cardiotonic Steroid that Singularly Stimulates Sodium Potassium Pump Activity at Low Doses

Rationale: Cardiotonic steroids (CTS), such as digoxin, have been used to treat heart failure (HF) for over 200 years. They inhibit the sodium-potassium pump (NKP), and increase cardiac contractility by inhibiting efflux of sodium through the pump (“digitalis hypothesis”). CTS possess three structural components: a saturated/unsaturated lactone ring, steroid core, and sugar moiety, each of which may be involved in NKP inhibition/stimulation. It is now known that inhibition of the NKP in patients with HF increases mortality, and all major beneficial treatments increase its activity. Endogenous circulating CTS such as ouabain are generally thought to inhibit the NKP, despite studies sporadically reporting ouabain-induced pump stimulation. This study aims to identify whether ouabain-induced pump stimulation occurs, and if so, which structural components are involved in causing pump stimulation. Methods & Results: Cardiac myocytes were isolated from male New Zealand White rabbits, placed in a Tyrode’s solution, and whole-cell patch clamped. They were exposed to 0-30nM ouabain, 0-50nM dihydroouabain (ouabain with a saturated lactone ring) or 0-500nM ouabagenin (ouabain lacking a sugar moiety) for 1 min, followed by a potassium-free solution, with the difference in current yielding the NKP current. Compared to the 0.47±0.05 pA/pF Tyrode’s solution control (n=11), 5nM ouabain significantly increased NKP current to 0.69±0.09 pA/pF ( P <0.05, n=6). Exposure to dihydroouabain or ouabagenin did not significantly change NKP current in the studied concentration range. Cell viability assays carried out on the breast cancer cell line MCF7, which have an NKP structure extremely similar to that of cardiomyocytes, showed significantly elevated viability above control values (n=2) following 24h treatment with 0-9nM ouabain; maximum viability was 116±5% at 0.28nM ( P <0.05, n=4). A significant change in viability was not observed for ouabagenin or digoxin in the same concentration range. Conclusion: Low-dose ouabain uniquely stimulates NKP activity. Low-dose dihydroouabain and ouabagenin do not, suggesting that a sugar moiety and unsaturated lactone ring are required for pump stimulation. Ouabain in its unaltered form may be a potential treatment for HF.

Calcium Current Properties and Leak Conductance in Mouse Muscle Fibers Overexpressing a Type 1 Hypokalemic Periodic Paralysis Mutant L-Type Calcium Channel

Missense mutations in the gene encoding the alpha1 subunit of the L-type calcium channel CaV1.1 induce type 1 Hypokalemic Periodic Paralysis (HypoPP1). These mutations mainly occur at arginine residues in the fourth transmembrane segment of voltage-sensor domains. Very few studies have investigated the acute effects of these mutations on channel function and muscle membrane electrical properties because of the difficulty to express Cav1.1 in heterologous systems. In the present study we successfully transferred by electroporation the genes encoding the turboGFP-tagged human wildtype (WT) and R1239H HypoPP1 mutant Cav1.1 into hind limb mouse muscles. The expression profile of the two channels showed a regular striated pattern indicative of the localization of the channels in the t-tubule membrane. Measurement of the L-type current using the silicone-clamp technique showed that the maximal conductance and the voltage-dependence of the Cav1.1 channel were significantly reduced and shifted towards negative potentials respectively in fibers expressing R1239H Cav1.1 as compared to fibers expressing WT Cav1.1. Applying voltage ramps from a holding potential of 0, −20, −40 or −60 mV to −120 mV in the presence of an external low-chloride, sodium-free and potassium-free solution revealed a significant higher leak conductance measured between −80 and −120 mV in fibers expressing R1239H Cav1.1. Acidification of the external solution significantly increased the leak inward current, leak conductance and the fluorescence of an internally loaded pH indicator in fibers expressing R1239H. These data suggest that an elevated leak inward current, likely carrying protons, flows at resting membrane potentials in fibers expressing R1239H Cav1.1 and that acidification of the external medium following muscle exercise could contribute to favor the onset of muscle paralysis in HypoPP1.

HERG Activation Gating Is Rapid: Evidence from Gating-Current Recordings and MTSET Modification of the Voltage Sensor

Background The human ether-a-go-go related gene protein (hERG) K + channel (Kv11.1) plays a major role in cardiac action potential repolarization, and defects in its function/expression can lead to long QT syndrome. The channel's key physiologic function as the main repolarization current is attributable in part to its unconventional slow activation kinetics, which are an order of magnitude slower than other members of the voltage-gated potassium channel superfamily. Methods We recorded gating-currents of hERG channels in tsa201 cells in order to directly identify the rate-limiting step in the activation of hERG channels. Expression of hERG channels was optimized by subcloning channel cDNA into a pGW1H expression vector and transfection into tsa201 cells. Gating currents were recorded in NMG + -based potassium-free internal and external solutions. As well, we used MTS modification of an externally facing residue in S4, I521C, to track the time course of movement of the S4 voltage sensor. I521 was mutated to a cysteine residue expressed in Xenopus or tsa201 cells, and various thiol-modifying reagents were used to modulate hERG activation and deactivation kinetics. Results hERG gating currents recorded from tsa201 cells were observed to activate on a millisecond time scale with time constants of on-gating current movement at 0 mV of 3.7 and 11.3 ms, much faster than ionic current activation, with bimodal voltage dependence (V 1/2-1 = –36.6 mV, k 1 = 8.3 mV, V 1/2-2 = 42.8 mV, k 2 = 15.5 mV, r² = 0.9912; A1=26%). Direct outward movement of the S4 domain as tracked by the modification of hERG channel I521C by MTSET was complete at 50 ms for pulses to 0 mV and within 25 ms for pulses to +60 mV. Conclusions This study represents the first report of hERG gating currents observed from mammalian cells and the first report of rapid voltage sensor modification associated with activation in hERG channels. Gating current recordings from tsa201 cells and the rate of MTSET modification of hERG voltage sensors suggest that the delayed activation kinetics of hERG cannot be attributed to slow voltage sensor movement but may be rate limited by a slow coupling process to the opening pore.

Modelling the Membrane Potential Dependence on Non-Specific Cation Channels in Canine Articular Chondrocytes

In a previous report, we showed that the predominant ion channel in potassium-free solutions was a gadolinium III (Gd3+) sensitive non-specific cation channel, with functional characteristics similar to that expected for transient receptor potential (TRP) type channels.In this study reverse transcription-PCR (RT-PCR) was used to investigate the expression of TRP channels in canine articular chondrocytes. Both a mathematical model based on the Goldman-Hodgkin-Katz voltage equation and current clamp whole-cell electrophysiology were then used to investigate the effect of these channels on membrane potential (Vm).Chondrocytes isolated from canine articular cartilage were cultured for 5 days in Dulbeccos Modified Eagles Medium with 10% Foetal Calf Serum. For RT-PCR analysis, total RNA was extracted from first passage cells. Electrophysiological recording was carried out on first to third passage cells.RT-PCR analysis of chondrocyte mRNA, and subsequent sequencing of products, showed a member of the TRP vanilloid group of channels (TRPV4) to be present; sequence homology to the human TRPV4 was 94%. We have so far failed to find mRNA for the functionally similar TRPC3 and TRPC6 channels.Using whole-cell and single-channel data from our own experiments and the literature, our model predicts the membrane to be heavily dependent on the activity of TRPV4. Simulated block of all non-specific cation channels in the chondrocyte membrane leads to a predicted −27mV change in Vm. This prediction closely matches our current clamp experiments with 100μM Gd3+ inducing a −32 ± 1mV (n = 6) change of Vm.Previously, large-conductance chloride and voltage-sensitive potassium channels have been reported to be important in the maintenance of chondrocyte Vm. The data presented here showsthat the TRPV4 channel also has a significant contribution to maintenance of the chondrocyte Vm.

The role of slow potassium current in phenomena of voltage-dependent action of 4-aminopyridine in amphibian myelinated nerve fibres

The mechanism underlying the voltage-dependent action of 4-aminopyridine (4-AP) is investigated in experiments on amphibian myelinated nerve fibres (Rana ridibunda Pallas) by way of extracellular recording of electrical activity and using activators of potassium current (potassium-free solution and nitric oxide NO) and inhibitors of sodium current (tetrodotoxin). Measurement of action potential (AP) areas was used to evaluate the extent of general membrane depolarization during the activity of nerve fibres. Tetrodotoxin-induced decrease in general membrane depolarization (when the action potential amplitude was reduced by less than 20%) leads to an increase in the duration of depolarizing after-potential (DAP). This supports the dependence of time course of DAP in the presence of 4-AP on ratio of fast and slow potassium channels. In the absence of 4-AP, potassium-free solution and NO increase the potassium current through fast potassium channels (decreasing AP duration, reducing DAP and sometimes producing fast hyperpolarizing after-potential (HAP) after shortened AP), and in the presence of 4-AP these activators increase potassium current through unblocked slow potassium channels (making the development of slow HAP induced by 4-AP more rapid). The increase of slow HAP induced by 4-AP under the influence of potassium-free solution with NO supports the idea that slow HAP is due to activation of slow potassium channels and argues against the notion of removal of block of fast potassium channels. All analyzed phenomena of voltage-dependent action of 4-AP in amphibian myelinated nerve fibers can be accounted for by the activation of slow potassium current produced by membrane depolarization and a decrease of the amount of fast potassium channels involved in the membrane repolarization.

A Gadolinium-Sensitive Non-Specific Cation Channel In Canine Articular Chondrocytes

Non-specific cation channels are present in a number of cell membranes and can be activated by diverse cellular stimuli, allowing mono- and divalent cations to cross the cell membrane (Sanchez & Wilkins 2003). In the present study we used both inside-out and whole-cell patch clamp electrophysiology to characterise the predominant ion channel in potassium free solutions. Isolated chondrocytes were cultured for 7 to 9 days in Dulbeccos Modified Eagles Medium with 10% Foetal Calf Serum. Recording was carried out on first to third passage cells. For single channel data, membrane potential (Vm) was calculated as Vm = -Hp-Vj where Hp was the holding potential and Vj the calculated junction potential. Data are expressed as mean ± standard error. Single-channel activity reversed at a membrane potential of 3 ± 2mV (n = 5) in the presence of 196mM internal and 155mM external Na+, indicative of a non-specific cation channel. Mean slope conductance of the channel was calculated to be 67 ± 5pS (n = 5). This channel activity was seen in 53% of patches (32/61), with mean open probability of 0.6 at −40mV. 100μM gadolinium III reduced this open probability by 75 ± 9%. In identical solutions the predominant whole-cell current showed a reversal potential of 1 ± 5mV. 100μM gadolinium III inhibited whole-cell current by 85 ± 7%. The whole-cell current exhibited weak voltage sensitivity with Boltzmann parameters for slope and half maximal activation of k = 83mV and V1/2 = −38mV. The ion channels identified in these electrophysiological experiments may underlie the gadolinium-sensitive stretch-activated increases in calcium observed by Guilak et al (1999) in bovine tissue.

TNF-α differentially modulates ion channels of nociceptive neurons

Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine involved in the development and maintenance of inflammatory and neuropathic pain conditions. The mechanisms by which TNF-alpha elicits pain behavior are still incompletely understood. Numerous studies suggest that TNF-alpha sensitizes primary afferent neurons. Most recently, it was shown that TNF-alpha induced an enhancement of TTX-R Na(+) current in dorsal root ganglion (DRG) cells. In the present study, we have tested the effect of acute application of TNF-alpha on voltage-gated potassium, calcium and sodium channel currents as well as its influence on membrane conductance in isolated rat DRG neurons. We report that voltage-gated potassium channel currents of nociceptive DRG neurons are not influenced by TNF-alpha (100 ng/ml), while voltage-gated calcium channel currents were decreased voltage-dependently by -7.73+/-6.01% (S.D.), and voltage-activated sodium channels currents were increased by +5.62+/-4.27%, by TNF-alpha. In addition, TNF-alpha induced a significant increase in IV ramps at a potential of +20 mV, which did not exist when the experiments were conducted in a potassium-free solution, indicating that this effect is mainly the result of a change in potassium conductance. These different actions of TNF-alpha might help to explain how it sensitizes primary afferent neurons after nerve injury and thus facilitates pain.

Functional heterogeneity of the “transporter” of electrogenic ionic pump of the Lumbricus terrestris somatic myocyte membrane

Potential created by electrogenic ionic pumps under conditions of maximum activation in a warm standard ionic medium with K(+) after preincubation in cold potassium-free solution has two components: a higher ouabaine-insensitive "stationary" component, and a lower "regulatory" component sensitive to ouabaine, furosemide, and removal of Cl(-) or Ca(2+) from the medium. Functional heterogeneity of electrogenic ionic pumps is hypothesized implying the existence of two components: "stationary" (not regulated extracellularly) and "regulatory" (controlled and directly related to active Cl(-) transfer).

The resting potential of mouse Leydig cells: role of an electrogenic Na+/K+ pump.

Resting potentials (Vm) were measured in mouse Leydig cells, using the whole-cell patch-clamp technique. In contrast to conventional microelectrode measurements, where a biphasic potential was observed, we recorded a stable Vm around -32.2 +/- 1.2 mV (mean +/- SEM, n = 159), at 25 degrees C, and an input resistance larger than 2.7 x 109 W. Although Vm is sensitive to changes in the extracellular concentrations of potassium and chloride, the relationship between Vm and these ions' concentrations cannot be described by either the Goldman-Hodgkin-Katz or the Nernst equation. Perifusing cells with potassium-free solution or 10?3 M ouabain induced a marked depolarization averaging 20.1 +/- 3.2 mV (n = 9) and 23.1 +/- 2.8 mV, (n = 7), respectively. Removal of potassium or addition of ouabain with the cell voltage-clamped at its Vm, resulted in an inwardly directed current, due to inhibition of the Na+K+ATPase. The pump current increased with temperature with a Q10 coefficient of 2.3 and had an average value of -6.5 +/- 0.4 pA (n = 21) at 25 degrees C. Vm also varied strongly with temperature, reaching values as low as -9.2 +/- 1.2 mV (n = 22) at 15 degrees C. Taking the pump current at 25 degrees C and a minimum estimate for the membrane input resistance, we can see that the Na+K+ATPase could directly contribute with 17.7 mV to the Vm of Leydig cells, which is a major fraction of the ?32.2 +/- 1.2 mV (n = 159) observed.

The Effects of 0.45% and 0.9% Saline Solutions on Serum Sodium Concentrations in Chronic Renal Failure Patients

Background: To choose optimal potassium free solutions in chronic renal failure patients, we studied the effects of 0.45% or 0.9% saline solutions on the serum sodium concentrations of patients undergoing kidney transplantation surgery. Methods: Sixty two patients, ASA physical status III-IV, undergoing kidney transplantation surgery, were allocated to receive either 0.45% saline (n = 26) or 0.9% saline solutions (n = 36). The patients received 2 L of 0.45% or 0.9% saline solutions with a CVP of 10 mmHg prior to a renal vein anastomosis. Serum sodium and potassium concentrations were measured before (Na0, K0) and after the administration of 2 L of 0.45% or 0.9% saline solutions (Na2, K2), respectively. Results: Serum sodium concentrations decreased after the administration of 0.45% saline solutions, and after administrating 2 L of 0.9% saline, the serum sodium concentrations increased in patients with baseline serum sodium concentrations lower than 136 mEq/L. When we administered 0.9% saline, which had a sodium concentration lower than the serum sodium concentration, the serum sodium concentration measured after 2 L of 0.9% saline infusion proportionally decreased in patients with baseline serum sodium concentration greater than 136 mEq/L (P ＜ 0.001). Conclusions: For ideal fluid selection in chronic renal failure patients, this study suggests a 0.45% saline solution for chronic renal failure patients with a baseline serum sodium concentration below the normal range and a 0.9% saline solution for patients with a baseline sodium concentration within the normal range.

Increase in Blood Pressure with Enhanced Na+, K+-ATPase Activity in Stroke-Prone Spontaneously Hypertensive Rats after 4-Weeks Intake of Rapeseed Oil as the Sole Dietary Fat

Twenty stroke-prone spontaneously hypertensive rats were divided into 2 groups of 10 animals each, and fed a defatted diet and orally administered rapeseed (canola) oil or soybean oil at 10 (w/w)% of the consumed diet once a day for 4 weeks. At the 4th week of administration, the systolic blood pressure in the canola oil group was higher (235 +/- 2 mmHg, mean +/- S.E.M., N=10) than that in the soybean oil group (225 +/- 4 mmHg, N=10, P<0.05). In isolated, perfused mesenteric bed from these rats, the increase in perfusion pressure by norepinephrine, ATP, arachidonic acid, endothelin-1, angiotensin II or serotonin showed no between-group differences. There were also no between-group differences in the production of thromboxane A2 and prostaglandin 12 in the outflow by arachidonic acid injection. On the other hand, in the isolated aortic ring from the canola oil group, developed tension in potassium-free solution was enhanced with activation of Na+, K+ -ATPase. These results suggest that canola oil intake as the sole dietary fat increases systolic blood pressure of stroke-prone spontaneously hypertensive rats. The changes in vascular responsiveness to vasoconstrictors and production of prostanoids are unlikely to have relevance to the elevation of blood pressure. However, altered Na+, K+ -ATPase activity may play a role in the promotion of blood pressure elevation.

Effects of l-amphetamine on the central neurons of the snail

The effects of l-amphetamine on the spontaneous firing of central neurons of African snails ( Achatina fulica Ferussac) were studied electrophysiologically. The effects of dopamine, noradrenaline, d-amphetamine, and methamphetamine on the central neurons also were tested. The l- and d-amphetamines (0.3 mM) elicited bursting firing of action potentials in the RP4 neuron of the snail, whereas dopamine (0.3 mM), noradrenaline (NE, 0.3 mM), and methamphetamine (2 mM) did not. The bursting firing of action potentials elicited by l-amphetamine was decreased if potassium-free solution, sodium-free solution, or solution containing oubain (0.1 mM), a sodium pump inhibitor, was perfused. The results suggested that l-amphetamine did, and methamphetamine did not, elicit a sodium-dependent bursting firing of action potentials of the neuron.

Loss of Shaker K Channel Conductance in 0 K + Solutions: Role of the Voltage Sensor

In potassium-free solutions some types of K channels enter a long-lasting nonconducting or “defunct” state. It is known that Shaker K channels must open in K +-free solutions to become defunct. Gating current studies presented here indicate an abnormal conformation in the defunct state that restricts S4 movement and alters its kinetics. Thus an abnormality initiated in the P region spreads to the gating apparatus. We find that channels most readily become defunct on repolarization to an intermediate voltage, thus prolonging occupancy of one of the several intermediate closed states. The state dependence of becoming defunct was further dissected by using the gating mutant L382A. Simply closing this channel at 0 mV (reversing the last activation step) does not make the mutant channel defunct. Instead, it is necessary to move further left (more fully closed) in the activation sequence. This was confirmed with ShIR experiments showing that channels become defunct only if there is inward gating charge movement. Rapid transit through the intermediate states, achieved at very negative voltage, is relatively ineffective at making channels defunct. Several mutations that removed C-type inactivation also made the channels resistant to becoming defunct. Our results show that normal gating current cannot be stably recorded in the absence of K +.

Fast inactivation in Shaker K+ channels. Properties of ionic and gating currents.

Fast inactivating Shaker H4 potassium channels and nonconducting pore mutant Shaker H4 W434F channels have been used to correlate the installation and recovery of the fast inactivation of ionic current with changes in the kinetics of gating current known as "charge immobilization" (Armstrong, C.M., and F. Bezanilla. 1977. J. Gen. Physiol. 70:567-590.). Shaker H4 W434F gating currents are very similar to those of the conducting clone recorded in potassium-free solutions. This mutant channel allows the recording of the total gating charge return, even when returning from potentials that would largely inactivate conducting channels. As the depolarizing potential increased, the OFF gating currents decay phase at -90 mV return potential changed from a single fast component to at least two components, the slower requiring approximately 200 ms for a full charge return. The charge immobilization onset and the ionic current decay have an identical time course. The recoveries of gating current (Shaker H4 W434F) and ionic current (Shaker H4) in 2 mM external potassium have at least two components. Both recoveries are similar at -120 and -90 mV. In contrast, at higher potentials (-70 and -50 mV), the gating charge recovers significantly more slowly than the ionic current. A model with a single inactivated state cannot account for all our data, which strongly support the existence of "parallel" inactivated states. In this model, a fraction of the charge can be recovered upon repolarization while the channel pore is occupied by the NH2-terminus region.

Age-dependent variations in potassium sensitivity of A-currents in rat hippocampal neurons.

Hippocampal pyramidal neurons were either cultured from prenatal rats or acutely isolated from the brain of newborn and juvenile rats. The influence of lowering the concentration of the extracellular potassium concentration ([K+]o) on isolated fast transient outward K+ currents (I(A)) was studied in these neurons using the patch clamp technique in the whole cell configuration. With respect to the response of I(A) to lowering [K+]o, three types of cells were observed. The first subpopulation of neurons was characterized by a complete suppression of I(A) over the whole voltage range under potassium-free solutions (type A neurons). A second proportion of cells showed an increase of I(A) at test pulses below -0 mV and a decrease of I(A) at voltages above -0 mV (type B neurons). In a third group of neurons, amplitudes of I(A) increased at all potentials tested during omission of potassium ions from the extracellular superfusate (type C neurons). Whereas type A and type B neurons were preferentially found in freshly plated cultures and newborn rats, the majority of type C cells was detected in long-term cultures and in animals of older ages. Thus, hippocampal A-currents lose their sensitivity to extracellular potassium ions during early ontogenesis.

Neurohumoral control of ionic pumping in molluscan muscle: III. Cholinergic control of the response to low potassium levels

1. 1. Isolated radular protractor muscles (RPM) of Busycon canaliculatum show a complex response to potassium free solution. 2. 2. While exposed to a bathing solution lacking K +, the RPM begins to respond with a hyperpolarizing phase. Within minutes, this gives way to a depolarizing phase (DP). After readmission of a bathing solution containing K +, there is an extra hyperpolarizing phase. 3. 3. Acetylcholine over a range of concentrations from 10 −8M to 10 −3M progressively enhances the DP. 4. 4. The action of acetylcholine is sodium dependent.

Altered electrical properties of bladder smooth muscle in streptozotocin‐induced diabetic rats

To examine the alterations in the electrical properties of bladder smooth muscle in rats with diabetes mellitus (DM) induced by streptozotocin. The study comprised 34 control rats and 20 with DM induced experimentally by injection with streptozotocin. At 10-15 weeks after the induction of DM, control and treated rats were killed, the bladder removed and the electrical responses of membranes from the detrusor smooth muscle recorded using intracellular microelectrodes. The resting membrane potential of the smooth muscle remained unaltered by DM but the frequency of spontaneous spike discharges sensitive to nicardipine was decreased. Transmural nerve stimulation elicited a purinergic excitatory junction potential (EJP) in muscles from both types of rat, but the threshold intensity of stimulation required to evoke an EJP was higher in muscle from the diabetic rat. Furthermore, EJPs large enough to trigger a nicardipine-sensitive spike potential could be elicited easily in muscles from the control rat, but not in muscles from diabetic rats. Stimulation of muscarinic receptors with exogenous acetylcholine (ACh) caused greater depolarization in muscle from diabetic rats. Stimulation of purinergic receptors with alpha, beta-methylene ATP caused a similar depolarization in both groups of rats. Application of potassium-free solution or ouabain depolarized the membrane by about 9 mV or 5 mV, respectively, in muscles from both groups of rat. Removal of potassium-free solution produced an ouabain-sensitive transient hyperpolarization which was larger in muscle from control rats, indicating that the potency of the Na-K pump was weakened in rats with DM. In the detrusor smooth muscle of rats with DM, there were fewer spontaneous spike discharges, supersensitivity of post-junctional muscarinic receptors, reduced potency of the post-junctional Na-K pump and a decrease in the release of neurotransmitter, possibly due to the impairment of prejunctional activity.

High calcium diet reduces blood pressure in exercised and nonexercised hypertensive rats.

The effects of long-term high calcium diet and physical exercise and their combined effects on the development of hypertension, plasma and tissue atrial natriuretic peptide, and arterial function were studied in spontaneously hypertensive rats with Wistar-Kyoto rats serving as normotensive controls. Hypertensive rats were made to exercise by running on a treadmill up to 900 m/day. Calcium supplementation was instituted by increasing the calcium content of the chow from 1.1% to 2.5%. During the 23-week study, calcium supplementation attenuated the rise in blood pressure in both trained and nontrained hypertensive animals, whereas exercise training had no significant effect on blood pressure. The high calcium diet alone was associated with reduced plasma and ventricular tissue contents of atrial natriuretic peptide, both of which were increased by exercise. Responses of mesenteric arterial rings in vitro were examined at the end of the study. Neither increased dietary calcium nor endurance training affected the contractile sensitivity of endothelium-intact preparations to potassium chloride or norepinephrine. However, a high calcium diet enhanced the arterial relaxation induced by the return of potassium to the organ bath upon precontraction with potassium-free solution, and also moderately augmented relaxations to acetylcholine, sodium nitrite, and isoproterenol. Exercise training did not affect the potassium relaxation rate, but enhanced responses to acetylcholine, isoproterenol, and sodium nitrite. In conclusion, enhanced arterial potassium relaxation, a response reflecting the function of the vascular sodium pump, paralleled well the long-term blood pressure lowering action of increased dietary calcium intake in exercised and nonexercised hypertensive rats. However, augmented arterial relaxation to agonists could also be observed in the absence of reduced blood pressure following regular physical exercise.

Endothelial modulation of ouabain-induced contraction and sodium pump activity in aortas of normotensive Wistar-Kyoto and spontaneously hypertensive rats.

The influence of vascular endothelium on ouabain-induced contractions and sodium pump activity in aortic segments of Wistar-Kyoto (WKY) and spontaneously hypertensive rat (SHR) was analyzed. De-endothelialization increased and reduced ouabain-induced contractions in WKY and SHR segments, respectively. The effects of de-endothelialization were not reproduced by pretreatment of the segments with NG-nitro-L-arginine methyl ester, indomethacin, or 5, 8, 11, 14-eicosatetraenoic acid, acetyl salicylic acid, dazoxiben, phosphoramidon, BQ-123, or superoxide dismutase. Bioassay experiments suggest that ouabain releases a diffusible factor from endothelial cells that inhibits or facilitates digitalis-induced contractions in WKY and SHR segments, respectively. In a potassium-free solution, potassium-induced relaxation in segments of both strains was abolished by ouabain in de-endothelialized aortas and reduced in intact ones. Ouabain-sensitive 86Rb+ uptake was significantly reduced by de-endothelialization both in WKY and in SHR. These results suggest that the vascular endothelium of WKY and SHR aortas releases a diffusible factor that stimulates the sodium pump and/or protects it from ouabain blockade. Ouabain also releases a diffusible endothelium-derived factor in SHR aortas that facilitates ouabain-induced contractions.