Intracellular Potassium Activity Research Articles

Augmentation and ionic mechanism of effect of β-N-methylamino- l-alanine in presence of bicarbonate on membrane potential of Retzius nerve cells of the leech Haemopis sanguisuga

The role of neurotoxic non-protein amino acid beta-N-methylamino- l-alanine (L-BMAA) as a putative causative agent of Western pacific amyotrophic lateral sclerosis/Parkinsonism dementia complex (ALS/PDC) has recently been reinvigorated. In view of this data we have investigated the strength and mechanism of effect of L-BMAA in presence of 20 mmol/L bicarbonate (a cofactor for BMAA) on membrane potential of the Leech Haemopis sanguisuga. Our results show that L-BMAA has excitatory effect in bicarbonate containing solution, which is more potent than in nominally bicarbonate free solution. This potentiation by bicarbonate is L-BMAA specific, as it was not exhibited by beta-N-oxalylamino- l-alanine. The effect of L-BMAA was partially blocked by non-NMDA receptor antagonist CNQX. Application of L-BMAA caused a decrease in input membrane resistance, an increase of intracellular sodium activity, and a decrease of intracellular potassium activity. Present findings indicate that BMAA could initiate excitotoxicity through activation of non-NMDA ionotropic glutamate receptors.

Fluorescent nanosensors for intracellular chemical analysis: decyl methacrylate liquid polymer matrix and ion-exchange-based potassium PEBBLE sensors with real-time application to viable rat C6 glioma cells.

Fluorescent spherical nanosensors, or PEBBLEs (probes encapsulated by biologically localized embedding), in the 500 nm-1 microm size range have been developed using decyl methacrylate as a matrix. A general scheme for the polymerization and introduction of sensing components creates a matrix that allows for the utilization of the highly selective ionophores used in poly(vinyl chloride) and decyl methacrylate ion-selective electrodes. We have applied these optically silent ionophores to fluorescence-based sensing by using ion-exchange and highly selective pH chromoionophores. This allows the tailoring of selective submicrometer sensors for use in intracellular measurements of important analytes for which selective enough fluorescent probes do not exist. The protocol for sensor development has been worked out for potassium sensing. It is based on the BME-44 ionophore (2-dodecyl-2-methyl-1,3-propanediylbis[N-[5'nitro(benzo-15-crown-5)-4'-yl]carbamate]). The general scheme should work for any available ionophore used in PVC or decyl methacrylate ion-selective electrodes, with minor adjustments to account for differences in ionophore charge and analyte binding constant. The reversible and highly selective sensors developed have a subsecond response time and an adjustable dynamic range. Applications to live C6 glioma cells demonstrate their utility; the intracellular potassium activity is followed in real time upon extracellular administration of kainic acid.

Basolateral potassium channels and epithelial ion transport.

Basolateral potassium channels and epithelial ion transport.

Effects of hypoxia on the intracellular K + of clustered and isolated glomus cells of mice and rats

Carotid bodies of rats and mice were used to measure the intracellular potassium activity,a i(K), of clustered and isolated glomus cells normally oxygenated (pO 2 102–139 Torr), and during hypoxia (pO 2 2–82 Torr) induced by Na-dithionite.a i(K) was measured with intracellular ion-selective microelectrodes, and the resting potential (E M) with KCl-filled micropipettes. Under normoxia, thea i(K) of clustered cells in both species was higher than that of isolated cells. This resulted in more negative potassium equilibrium potentials (E K's). There was no correlation betweena i(K) andE M in clustered cells, but this correlation was significant in isolated cells. Hypoxia significantly decreaseda i(K) in clustered and single mouse cells, and in clustered rat cells, although its effects on single rat cells were variable.a i(K) decreases were accompanied by cell depolarization and positive shifts inE K. During hypoxia, there were significant correlations betweena i(K) andE M in all cells. It is suggested thata i(K) did not influence theE M of clusstered cells under normoxia because of interference by K + pumping mechanisms toward glomus cells from surrounding sustentacular processes. This hindrance is not present when glomus cells are isolated. During hypoxia K + pumping from sustentacular cells is disrupted, allowing theE M of clustered glomus cells to follow theira i(K) and behave like isolated cells. The different effects of hypoxia on isolated rat and mouse cells may be due to activation of different types of glomus cells.

The effect of tri-iodothyronine on the membrane potential and intracellular sodium and potassium activities of rat soleus and extensor digitorum longus muscles.

Tri-iodothyronine (T3) induces a considerable increase in the number of Na/K pump units in rat skeletal muscles, but this effect is more pronounced in red muscles, such as soleus, than in white muscles such as extensor digitorum longus (EDL). In the present study, the effect of T3 on the membrane potential (Em) and the intracellular activities of K+ and Na+ (aKi and aNai) in the two muscle types has been studied using microelectrodes. Hyperthyroidism was induced by seven subcutaneous injections of 50 micrograms T3 per 100 g body weight on alternate days. Following treatment of rats with T3, the mean T3 concentration in the serum was 8.4 +/- 0.46 nmol/l (S.D.) compared with 1.1 +/- 0.16 nmol/l in the serum of untreated control rats, and the heart weight/body weight ratio of the treated rats had increased from 0.29 +/- 0.01 in control rats to 0.39 +/- 0.02. In soleus muscle fibres from the T3-treated rats, the Em, aKi and aNai were unchanged, whereas, in EDL muscle fibres from these rats, the Em had depolarized by 2 mV (P < 0.01) and aNai had increased by 2 mmol/l (P < 0.05). Since T3 induces not only an increase in the number of pump units and active movement of Na+ and K+ but also an increase in the passive fluxes of these ions, the results are discussed in terms of these two opposing ionic movements.

Intracellular sodium and potassium activities of skeletal muscle fibres of hypothyroid rats.

In soleus muscle fibres of hypothyroid rats, the membrane potential (Vm) and the intracellular K+ activity (aKi) were significantly lower than in control muscles. These results are consistent with the well-documented decrease in the number of Na(+)-K+ pumps which occurs in hypothyroid muscles. aNai was unchanged in the hypothyroid muscles but this may reflect a change in passive Na+ fluxes which has been reported to occur in association with changes in the number of pump units.

Intracellular pH changes induced by hypoxia and anoxia in isolated sheep heart Purkinje fibres

The effects were studied of hypoxia on intracellular ion activities in sheep heart Purkinje fibres. The intracellular pH (pHi), surface pH (pHs), intracellular potassium activity (aki), and intracellular sodium activity (aNai) of the cells were recorded using liquid ion exchanger-filled microelectrodes. Various methods of inhibiting oxidative phosphorylation were compared for their effect on pHi. These methods were the use of hypoxia, anoxia or NaCN (2 mM). Hypoxia was produced by degassing solutions under reduced pressure then bubbling with 100% nitrogen gas. Anoxia was produced in a similar manner but with the addition of the reducing agent sodium dithionite (0.5 mM) to remove all traces of oxygen from the solutions. Anoxia caused the most marked changes. Concentration of sodium dithionite between 0.1 and 1 mM produced similar maximum rates of acidification. High concentrations (5 or 20 mM) could produce larger intracellular acidifications apparently unrelated to anoxia. The effects of hypoxia and NaCN were similar. Inhibition of Na(+)-H+ exchange with amiloride (1 mM) had little effect on the pH changes produced by hypoxia. Periods of hypoxia exceeding 1 h still resulted in rapid, readily reversible changes in pHi. Hypoxia caused a rise in aNai, the effect being larger in anoxic conditions. The intracellular K+ activity decreased in hypoxia with further decreases in anoxic conditions. The intracellular ion changes produced during hypoxia are discussed in terms of the production of lactic acid by the cells and changes in the ATP supply to the Na(+)-K+ pump.

Effect of anoxia on intracellular and extracellular potassium activity in hypoglossal neurons in vitro

1. A brain slice preparation was used to study the hypoglossal (XII) neuronal response to anoxia. Both intra- and extracellular potassium activities (K+i,K+o) were measured by the use of ion-selective microelectrodes, and K+ flux was assessed by the use of pharmacologic blockers. 2. Extracellular recordings showed that a short period of anoxia (4 min) induced an increase in K+o of 26.4 +/- 7.5 mM (mean +/- SD, n = 20) in the XII nucleus of adult rats. 3. Intracellular recordings (n = 31) in XII neurons showed a substantial decrease in K+i during anoxia. Fourteen neurons were analyzed in detail and these showed that XII neurons depolarized to -25.3 +/- 7.7 mV, whereas K+i dropped from 93.6 +/- 14.9 to 32 +/- 9.0 mM. These results strongly suggested that K+ is lost from XII neurons during anoxia. 4. Although the extracellular space (ECS) shrank by approximately 50% during anoxia, the possibility that the increase in K+o and decrease in K+i were mainly caused by shrinkage of the ECS and swelling of intraneuronal space was excluded to a great degree because the changes in K+i and K+o during anoxia were relatively very large. 5. To study the mechanisms by which K+ is lost from XII neurons, we used several pharmacologic blockers. High concentration of ouabain (10 mM) and strophanthidin (80 microM) increased K+o from baseline (3-4 mM) to 40.9 +/- 2.5 mM (n = 6) but did not abolish an additional anoxia-induced increase in K+o, suggesting that mechanisms other than Na(+)-K(+)-adenosine triphosphatase inhibition were also responsible for the anoxia-induced K+ leakage.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular potassium activity in mammalian proximal tubule: Effect of perturbations in transepithelial sodium transport

Intracellular potassium activity (alpha Ki) was measured in control conditions in mid-cortical rabbit proximal convoluted tubule using two methods: (i) by determination of the K+ equilibrium potential (EK) using Ba(2+)-induced variations in the basolateral membrane potential (VBL) during transepithelial current injections and (ii) with double-barrel K-selective microelectrodes. Using the first method, the mean VBL was -48.5 +/- 3.2 mV (n = 16) and the mean EK was -78.4 +/- 4.1 mV corresponding to alpha Ki of 68.7 mM. With K-selective microelectrodes, VBL was -36.6 +/- 1.1 mV (n = 19), EK was -64.0 +/- 1.1 mV and alpha Ki averaged 40.6 +/- 1.7 mM. While these last EK and VBL values are significantly lower than the corresponding values obtained with the first method (P less than 0.001 and P less than 0.01, respectively), the electrochemical driving force for K transport across the basolateral membrane (microK = VBL-EK) is not significantly different for both techniques (30.1 +/- 3.3 mV for the first technique and 27.6 +/- 1.8 mV for ion-selective electrodes). This suggests an adequate functioning of the selective barrel but an underestimation of VBL by the reference barrel of the double-barrel microelectrode. Such double-barrel microelectrodes were used to measure temporal changes in alpha Ki and microK in different experimental conditions where Na reabsorption rate (JNa) was reduced. alpha Ki was shown to increase by 12.2 +/- 2.7 (n = 5) and 14.1 +/- 4.4 mM (n = 5), respectively, when JNa was reduced by omitting in the luminal perfusate: (i) 5.5 mM glucose and 6 mM alanine and (ii) glucose, alanine, other Na-cotransported solutes and 110 mM Na. In terms of the electrochemical driving force for K exit across the basolateral membrane, microK, a decrease of 5.4 +/- 2.0 mV (P less than 0.05, n = 5) was measured when glucose and alanine were omitted in the luminal perfusate while microK remained unchanged when JNa was more severely reduced (mean change = -1.7 +/- 2.1 mV, NS, n = 5). In the latter case, this means that the electrochemical driving force for K efflux across the basolateral membrane has not changed while both the active influx through the Na-K pump and the passive efflux in steady state are certainly reduced. If the main pathway for K transport is through the basolateral K conductance, this implies that this conductance must have decreased in the same proportion as that of the reduction in the Na-K pump activity.

Intracellular potassium activity and the role of potassium in transepithelial salt transport in the human reabsorptive sweat duct

We have measured the intracellular potassium activity, [K+]i and the mechanisms of transcellular K+ transport in reabsorptive sweat duct (RSD) using intracellular ion-sensitive microelectrodes (ISMEs). The mean value of [K+]i in RSD is 79.8 +/- 4.1 mM (n = 39). Under conditions of microperfusion, the [K+]i is above equilibrium across both the basolateral membrane, BLM (5.5 times) and the apical membrane, APM (7.8 times). The Na+/K+ pump inhibitor ouabain reduced [K+]i is insensitive to the Na+/K+/2 Cl- cotransport inhibitor bumetanide in the bath. Cl- substitution in the lumen had no effect on [K+]i. In contrast, Cl- substitution in the bath (basolateral side) depolarized BLM from -26.0 +/- 2.6 mV to -4.7* +/- 2.4 mV (n = 3; *indicates significant difference) and decreased [K+]i from 76.0 +/- 15.2 mM to 57.7* +/- 12.7 mM (n = 3). Removal of K+ in the bath decreased [K+]i from 76.3 +/- 15.0 mM to 32.3 +/- 7.6 mM (n = 4) while depolarizing the BLM from -32.5 +/- 4.1 mV to -28.3* +/- 3.0 mV (n = 4). Raising the [K+] in the bath by 10-fold increased [K+]i from 81.7 +/- 9.0 mM to 95.0* +/- 13.5 mM and depolarized the BLM from -25.7 +/- 2.4 mV to -21.3* +/- 2.9 mV (n = 4). The K+ conductance inhibitor, Ba2+, in the bath also increased [K+]i from 85.8 +/- 6.7 mM to 107.0* +/- 11.5 mM (n = 4) and depolarized BLM from -25.8 +/- 2.2 mV to -17.0* +/- 3.1 mV (n = 4). Amiloride at 10(-6) M increased [K+]i from 77.5 +/- 18.8 mM to 98.8* +/- 21.6 mM (n = 4) and hyperpolarized both the BLM (from -27.5 +/- 1.4 mV to -46.0* +/- 3.5 mV, n = 4). However, amiloride at 10(-4) M decreased [K+]i from 64.5 +/- 0.9 mM to 36.0* +/- 9.9 mM and hyperpolarized both the BLM (from -24.7 +/- 1.4 mV to -43.5* +/- 4.2 mV) and APM (from -18.3 +/- 0.9 mV to -43.5* +/- 4.2 mV, n = 6). In contrast to the observations at the BLM, substitution of K+ or application of Ba2+ in the lumen had no effect on the [K+]i or the electrical properties of RSD, indicating the absence of a K+ conductance in the APM.(ABSTRACT TRUNCATED AT 400 WORDS)

Ion Activities and Electrochemical Gradients in the Mealworm Rectal Complex

ABSTRACT Ion activities and potential differences in cellular and extracellular compartments of the rectal complex of Tenebrio molitor L. larvae have been recorded simultaneously using double-barrelled ion-sensitive microelectrodes. On average, the tubule lumen (TL) was 44mV positive to the haemolymph. Values of aK in the posterior rectal complex exceeding 2700 mmol I-1 were measured, sufficient to account for much of the osmolality of 6.8osmolkg-1 driving uptake of water from the rectal lumen. The mean value of 797 mmol l-1 exceeded the Nernst equilibrium activity more than 75-fold, indicating active transport of K+. Intracellular potassium activities in the tubules (153 mmol l-1) were high relative to the values in other insect cells, but moderate relative to TL values. Tubule lumen Na+ activities as high as 400 mmol l-1 and pH values of 6.8 were well above the equilibrium values of 11 mmol I-1 and 7.9, respectively, indicating active transport of these cations as well. The ease and frequency of impaling a perinephric space (PNS) surrounding the tubules established it as a functional compartment. On average, the PNS was 22 mV negative to the haemolymph. Potassium activities in the PNS were close to electrochemical equilibrium with the haemolymph, whereas mean aNa and pH were reduced fivefold and 0.5 units, respectively, below the corresponding Nernst equilibrium values. The results suggest that cations move from haemolymph to PNS, and that the PNS is the immediate source for cation transport into the tubule lumen. Cl- was close to electrochemical equilibrium with the haemolymph in both compartments, and presumably enters the tubule lumen as a passive consequence of positive potential differences (PDs) in the tubule lumen.

Effect of lithium on the intracellular potassium concentration in sheep heart Purkinje fibres

Simultaneous measurements were made of the intracellular activities of potassium and lithium in sheep heart Purkinje fibres using ion-sensitive microelectrodes. On exposure of the fibres to lithium, the intracellular activity of lithium rose, with an equivalent decrease in the level of intracellular potassium.

Intracellular sodium and potassium activities in “diseased” human atrium: The role of electrogenic Na pump in producing the low resting potential

Intracellular sodium and potassium activities in “diseased” human atrium: The role of electrogenic Na pump in producing the low resting potential

Intracellular pH of canine subendocardial Purkinje cells surviving in 1-day-old myocardial infarcts.

A large reduction of intracellular potassium activity in depolarized subendocardial Purkinje fibers 24 hours after coronary artery ligation is accompanied by a much smaller increase in intracellular sodium activity. Similar intracellular ionic changes also occur during acute ischemia in ventricular muscle and are consistent with mechanisms based on intracellular acidification, which is known to occur in acutely ischemic muscle. To determine if canine subendocardial Purkinje cells 24 hours after myocardial infarction are also acidic, their intracellular pH, surface pH, and maximum diastolic potential (MDP) were measured with double-barrel pH-sensitive microelectrodes and compared with control fibers in noninfarcted hearts. In 12 mM bicarbonate Tyrode's solution (5% CO2-95% O2), the average intracellular pH was not significantly different (p greater than 0.25) for normal tissue (6.83 +/- 0.08, SD, MDP = -83.5 +/- 3.2 mV), for depolarized Purkinje fibers in infarct preparations during the first hour of superfusion (6.88 +/- 0.11, MDP = -47.8 +/- 11.8 mV), and for partially recovered Purkinje fibers in infarcts averaged over the third to sixth hours of superfusion (6.85 +/- 0.12, MDP = -74.5 +/- 9.6 mV). In 24 mM bicarbonate Tyrode's solution, infarct intracellular pH during both the first hour of superfusion (7.08 +/- 0.13, MDP = -57.6 +/- 15.7 mV) and during the third to sixth hours of superfusion (7.06 +/- 0.15, MDP = -76.5 +/- 9.6 mV) was significantly alkaline (p less than 0.0005) compared with average control pH (6.92 +/- 0.12, MDP = 82.1 +/- 3.7 mV). In 24 mM bicarbonate Tyrode's solution, the intracellular pH did vary with MDP (0.0032 pH units/mV). During superfusion of normal Purkinje fibers with hypoxic Tyrode's solution, intracellular pH acidified by 0.22 pH units as they depolarized. Therefore, intracellular acidification does not seem to be a cause of the depolarization of subendocardial Purkinje cells 24 hours after myocardial infarction.

Intracellular pH, Na+- and K+-activities at the onset of St. Thomas' cardioplegia: a study with ionselective microelectrodes.

Cellular edema and cardiac arrhythmias are often closely related to intracellular ionic alterations and, moreover, are an actual problem of clinical cardioplegia and ischemia of the heart. In order to investigate whether the clinically widely used cardioplegic solution of the St. Thomas' Hospital may predispose for these complications, membrane potential (EM), intracellular pH (pHi), and intracellular sodium and potassium activity (aiNa- and aiK) in sheep heart Purkinje fibres were directly measured by means of neutral-carrier ion-selective microelectrodes during equilibration of the fibres' extracellular space with the cardioplegic solution. The experimental temperature was 35 degrees C throughout. During control conditions under superfusion of a HEPES-buffered Tyrode solution EM was -74.4 +/- 5.1 mV (n = 39), pHi was 7.18 +/- 0.05 (n = 16), and aiNa and aiK were 7.6 +/- 1.4 mmol/l (n = 15) and 118.9 +/- 4.6 mmol/l (n = 15) respectively. Superfusing the Purkinje strand for 10 minutes with the cardioplegic St. Thomas' solution led to a depolarization to -57.3 +/- 4.7 mV (n = 21), a slight aiNa decrease to 6.7 +/- 1.6 mmol/l (n = 15; p less than 0.01; cardioplegic solution without procaine) and an increase of aiK to 127.1 +/- 4.4 mmol/l (n = 6; p less than 0.01). pHi needed 15 minutes to reach a steady state value of 7.25 +/- 0.05 (n = 9). The alterations on post-cardioplegic reperfusion with Tyrode solution were reversible within 15 minutes. Simulation of the clinical situation of ice-cold application of the solution by inhibiting the cellular Na/K pump via 0.1 mmol/l dihydroouabaine added to the St. Thomas' solution resulted in a marked increase of aiNa to 10.7 +/- 1.5 mmol/l (n = 6; p less than 0.01; no procaine) during cardioplegic superfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

K+-selective microelectrode study of internally dialyzed squid giant axons

Intracellular potassium activity, (aK)i, and axoplasmic K+ concentration, [K+]i, were measured by means of K+-selective microelectrodes and atomic absorption spectroscopy, respectively, in squid giant axons dialyzed with K+-free dialysis solution and bathed in K+-free artificial sea water. (aK)i measurements indicated that axoplasmic free K+ could be depleted by dialysis, whereas [K+]i measurements on axoplasm extruded from these axons suggest substantial retention of K+ (15.5 +/- 1.7 mmol/kg axoplasm K+; n = 9). In comparison, [K+]i in axoplasm extruded from freshly dissected axons was 330 +/- 16 mmol/kg axoplasm (n = 6). These data suggest that approximately 5% of the axoplasmic K+ ions are not easily removed by dialysis and that these ions are either bound to macromolecular sites or sequestered into membrane-enclosed organelles.

Transmembrane action potentials and intracellular potassium activity of baboon cardiac tissues

Preparations of baboon cardiac tissue were studied using standard microelectrode and double barrelled potassium ion selective microelectrode techniques. Transmembrane action potentials were recorded from Purkinje fibres and from atrial and ventricular muscle cells. Purkinje fibres were impaled frequently on the ventricular septum but were sparse on the endocardium of the free wall. Purkinje fibres had longer action potential durations than ventricular muscle cells, and endocardial muscle cells had longer action potential durations than epicardial muscle cells. Tissue bundles resembling the false tendons of the canine heart were found in the ventricles. Most of these false tendons consisted of ventricular muscle as indicated by transmembrane action potentials. On rare occasions, false tendon preparations were studied in which the cells had action potentials similar to those of canine Purkinje fibres. In these preparations, normal automaticity occurred from maximum diastolic potentials greater than or equal to -85 mV. Intracellular potassium activity in the baboon ventricular muscle cells was 96(3) mmol.litre-1 (mean(SEM), n = 32), which is lower than that reported for canine tissues but higher than that reported for feline or rabbit tissues. It is concluded that, although the cellular electrophysiology of primate and canine cardiac tissues is superficially similar, consistent and perhaps important differences do occur.

KCl co-transport across the basolateral membrane of rabbit renal proximal straight tubules.

Mammalian renal proximal tubules reabsorb large amounts of chloride. Mechanisms of the transcellular chloride transport are poorly understood. To determine whether KCl co-transport exists in the basolateral membrane of mammalian renal proximal tubule, isolated rabbit proximal straight tubules (S2 segment) were perfused in vitro, and intracellular activities of potassium and chloride (aKi, aCli) were measured by double-barreled ion-selective microelectrodes. aCli did not change when basolateral membrane voltage was altered by application of a direct current through perfusion pipette. aCli changes in response to bath chloride elimination were not affected by current application as well, indicating that the basolateral chloride transport is electroneutral. An increase in potassium concentration of the bath fluid from 5 to 20 mM reversibly increased aCli by 10 mM. This response of aCli to a change in the bath potassium concentration was also observed when luminal chloride was removed, or ambient sodium was totally removed. aKi significantly decreased by 5 mM when chloride was removed from the bath. These data demonstrate the existence of an electroneutral Na+-independent KCl co-transport in the basolateral membrane of the rabbit proximal tubule. Calculated electrochemical driving force was favorable for the movement of KCl from the cell to the peritubular fluid.

Effect of Ureteral Obstruction on Proximal Tubular Functions of Rat Kidney

The effect of complete unilateral ureteral obstruction (CUUO) on proximal tubular functions was studied in rats, using the K+-sensitive microelectrode technique and split oil drop method. In the control kidneys peritubular membrane potential (EMperi) and intracellular potassium activity (aKi) were −70.8 ± 7.0mV and 81.2 ± 22.0mEq/liter (mean ± SD), respectively. In the CUUO kidneys both EMperi and aKi were progressively reduced with the duration of obstruction. However, in all tubules aKi values were still above the electrochemical equilibrium. In the three days’ CUUO kidneys EMperi and aKi were −51.5 ± 11.7mV and 53.8 ± 22.8mEq/liter, respectively. Rate of fluid absorption (JVL;nl./sec. mm.) across the proximal tubular epithelium from Ringer solution in the control and three days’ CUUO kidneys was 0.029 and 0.0065 respectively. In the CUUO kidneys there were wide variations in JVL and EMperi, but there was a clear correlation between these two variables. JVL from choline chloride solution was negligible in both control and CUUO kidneys. From above results, it was suggested that the proximal tubular reabsorption primarily depending on the Na+-K+ pump might be reduced but still working in the CUUO kidney, and thus the proximal tubular reabsorption might take part in preservation of glomerular filtration during the obstruction.

Effect of acetylcholine on aconitine induced delayed afterdepolarisation in the frog atrium and ventricle.

The effect of acetylcholine on the aconitine induced delayed afterdepolarisation and triggered electrical activities under nominally calcium free conditions were studied in frog atrium and ventricle. The changes in intracellular potassium activity were also examined. The aconitine induced delayed afterdepolarisation and triggered electrical activities in atrial muscles were transiently suppressed by acetylcholine. This inhibition was correlated with the time course of the development of hyperpolarisation in the resting membrane potential during acetylcholine application. Propranolol did not abolish the transient inhibition of delayed afterdepolarisation during continuous application of acetylcholine, whereas atropine completely inhibited this effect of acetylcholine. Intracellular potassium activity decreased with time after acetylcholine application, whereas the resting potential became hyperpolarised at an early stage, showing slow recovery thereafter. These results indicate that the transient inhibition of delayed afterdepolarisation by acetylcholine is associated with transient hyperpolarisation of the membrane potential, which is assumed to be caused by potassium accumulation or desensitisation of the muscarinic receptor, or both.