Elevation Of Osmolality Research Articles

Salt and gene expression: evidence for [Na+]i/[K+]i-mediated signaling pathways.

Our review focuses on the recent data showing that gene transcription and translation are under the control of signaling pathways triggered by modulation of the intracellular sodium/potassium ratio ([Na+]i/[K+]i). Side-by-side with sensing of osmolality elevation by tonicity enhancer-binding protein (TonEBP, NFAT5), [Na+]i/[K+]i-mediated excitation-transcription coupling may contribute to the transcriptomic changes evoked by high salt consumption. This novel mechanism includes the sensing of heightened Na+ concentration in the plasma, interstitial, and cerebrospinal fluids via augmented Na+ influx in the endothelium, immune system cells, and the subfornical organ, respectively. In these cells, [Na+]i/[K+]i ratio elevation, triggered by augmented Na+ influx, is further potentiated by increased production of endogenous Na+,K+-ATPase inhibitors documented in salt-sensitive hypertension.

Meal consumption is ineffective at maintaining or correcting water balance in a desert lizard, Heloderma suspectum

Many xeric organisms maintain water balance by relying on dietary and metabolic water rather than free water, even when free water may be available. For such organisms, hydric state may influence foraging decisions, since meal consumption is meeting both energy and water demands. To understand foraging decisions it is vital to understand the role of dietary water in maintaining water balance. We investigated whether meal consumption was sufficient to maintain water balance in captive Gila monsters (Heloderma suspectum) at varying levels of dehydration. Gila monsters could not maintain water balance over long time scales through meal consumption alone. Animals fed a single meal took no longer to dehydrate than controls when both groups were deprived of free water. Additionally, meal consumption imparts an acute short-term hydric cost regardless of hydration state. Meal consumption typically resulted in a significant elevation in osmolality at 6 h post-feeding, and plasma osmolality never fell below pre-feeding levels despite high water content (~70%) of meals. These results failed to support our hypothesis that dietary water is valuable to Gila monsters during seasonal drought. When considered in conjunction with previous research, these results demonstrate that Gila monsters, unlike many xeric species, are heavily reliant on seasonal rainfall and the resulting free-standing water to maintain water balance.

Effects of epitheliocystis on serum lysozyme activity and osmoregulation in cultured juvenile striped trumpeter, Latris lineata (Forster)

Cultured juvenile striped trumpeter, Latris lineata (Forster), were sampled at two time points in spring (68 fish) and autumn (48 fish) to assess the prevalence and severity of epitheliocystis and associated physiological impacts. Prevalence of epitheliocystis was 49.2% in spring and 100% in autumn. Fish sampled in spring had low mean density of epitheliocystis induced cysts at 0.39±0.08 per cm2 whereas those fish sampled in autumn had significantly higher mean cyst density at 134.93±15.81 (p<0.05). The mean diameter of cysts did not differ and it was 47.9±3.41μm in spring and 50.7±0.50μm in autumn. The cysts were positioned at the tips or along lamellae. Host response was affected by the severity of infection. Histological examination revealed little host response in striped trumpeter with low densities of cysts; however proliferative responses, including lamellar fusion due to epithelial hyperplasia and inflammation, were present in fish that had higher cyst densities. Serum osmolality and lysozyme activity were positively correlated with the densities of cysts in juvenile striped trumpeter (p<0.001). Furthermore, the osmolality and lysozyme activity of infected striped trumpeter were significantly elevated compared with the non-infected striped trumpeter (p<0.05). Histological examination revealed the absence of chloride cells at the base of the gill lamellae in the vicinity of the cysts, which may explain the elevation of osmolality in the individuals affected by epitheliocystis. However, the counts of chloride cells in the interlamellar areas did not differ between the fish with high and normal osmolality (p>0.05). This study describes the first case of epitheliocystis in striped trumpeter and reports associated physiological effects.

Histone H2AX becomes phosphorylated in response to high NaCl in apoptotic cells, but not in viable ones

High NaCl induces DNA breaks. The breaks persist as long as NaCl remains elevated, but are rapidly repaired when NaCl is lowered. H2AX is phosphorylated in response to DNA damage from many causes, such as ionizing radiation, but whether this occurs in response to high NaCl has been controversial. In mIMCD3 cells H2AX does not become phosphorylated when osmolality is elevated to 500–600 mosmol/kg by adding NaCl (Am J Physiol Renal 285:F266,2003). In contrast, in HeLa cells elevation of osmolality to 500–600 mosmol/kg causes H2AX phosphorylation (Am J Physiol Renal 291:F1014,2006). The purpose of the present studies was to understand the difference. We find that 100% of mIMCD3 cells survive 24 hours after osmolality is increased to 500 mosmol/kg, but only 60% of Hela cells survive. Knowing that H2AX becomes phosphorylated during apoptosis, we identified apoptotic cells by fluorochrome labeling of activated caspases, and H2AX phosphorylation by immunostaining. Elevating NaCl to 500 mosmol/kg causes apoptosis in the HeLa cells and H2AX phosphorylation that is limited to the apoptotic cells. Exposure of HeLa cells to 400 mosmol/kg induces DNA breaks (Comet assay) without apoptosis or H2AX phosphorylation. We conclude that high NaCl‐induced DNA breaks do not cause H2AX phosphorylation in cells that survive, but that H2AX phosphorylation occurs in the cells that die by apoptosis. Supported by the Intramural Program of NHLBI

Tissue hyperosmolality and brain edema in cerebral contusion

Severe cerebral contusion is often associated with nonhemorrhagic mass effect that progresses rapidly within 12 to 48 hours posttrauma. The mechanisms underlying such a rapid progression of mass effect cannot be fully explained by classic concepts of vasogenic and cytotoxic brain edema. Data from previous clinical trials, including diffusion-weighted magnetic resonance imaging studies, have indicated that cells in the central (core) area of the contusion undergo shrinkage, disintegration, and homogenization, whereas cellular swelling is located predominately in the peripheral (rim) area during this period. The authors hypothesized that high osmolality within the contused brain tissue generates an osmotic potential across the central and peripheral areas or causes blood to accumulate a large amount of water. To elucidate the role of tissue osmolality in contusion edema, they investigated changes in tissue osmolality, specific gravity, and ion concentration in contused brain in both experimental and clinical settings. Their results demonstrated that cerebral contusion induced a rapid increase in tissue osmolality from a baseline level of 311.4 +/- 11.3 to 402.8 +/- 15.1 mOsm at 12 hours posttrauma (p < 0.0001). Specific gravity in tissue significantly decreased from 1.0425 +/- 0.0026 to 1.0308 +/- 0.0028 (p < 0.01), reflecting water accumulation in contused tissue. The total ionic concentration [Na+] + [K+] + [Cl-] did not change significantly at any time point. Inorganic ions do not primarily contribute to this elevation in osmolality, suggesting that the increase in colloid osmotic pressure through the metabolic production of osmoles or the release of idiogenic osmoles can be a main cause of contusion edema.

Dimethyl sulfoxide effects on hERG channels expressed in HEK293 cells

Introduction: Dimethyl sulfoxide (DMSO) is widely used as a solvent to facilitate formulation of test substances in cell perfusion solutions. However, DMSO concentration in bath (extracellular) solution is usually limited to 0.1–0.3% to avoid DMSO-induced changes in cell morphology and membrane properties due to elevation of osmolality. The purpose of this study was to examine whether DMSO-induced hyperosmotic effects on hERG expressing cells could be compensated by adding an equivalent amount of DMSO in pipette (intracellular) solution, to investigate DMSO effects on hERG channels, and to determine the impact of DMSO on the potency of hERG channel blockers. Method: Whole-cell patch clamp method was used to record hERG currents in HEK293 cells. DMSO at concentrations of 0.1% to 2% was applied to bath and pipette solutions. Various voltage protocols were used to examine DMSO effects on hERG channel properties and to evaluate DMSO impacts on the potency of terfenadine and E-4031. Results: When DMSO was added simultaneously in bath and pipette solutions, normal cell morphology and the proper current recording conditions could be maintained with application of up to 2% DMSO. DMSO slightly shifted the current–voltage relationship, activation curve, and inactivation curve of the hERG channel to more positive voltages. DMSO had little effect on the concentration–response relationship of hERG channel blockers we assessed. The IC 50 for terfenadine and E-4031 were not significantly changed in the presence of 0.3, 0.5, 1 and 2% DMSO. Discussion: Our results demonstrate that changes in cell morphology induced by extracellular DMSO can be prevented by application of DMSO in pipette solution. By utilizing this approach, we successfully performed hERG current recordings using bath solution containing up to 2% DMSO. DMSO-induced shifts of the voltage-dependence of hERG channel gating had little impact on the potency of hERG channel blockers.

Glutamatergic input in the PVN is important in renal nerve response to elevations in osmolality.

Elevations in plasma osmolality elicit reflex humoral and neural responses. The hypothalamic paraventricular nucleus (PVN) is important in humoral responses. We have investigated whether the PVN contributed to the renal nerve reduction that is normally elicited by increased plasma osmolality in the conscious rabbit. Renal sympathetic nerve activity (RSNA) was monitored after an intravenous infusion of hypertonic saline (1.7 M NaCl, 2 ml/min for 7 min). The responses were examined in animals microinjected with muscimol (10 nmol) into, and outside, the PVN to acutely inhibit neuronal function or with kynurenate (25 nmol) to block glutamate receptors. Compared with vehicle, the maximum reduction in RSNA elicited by hypertonic saline was significantly less with muscimol or kynurenate pretreatment into the PVN. A similar study with kynurenate was also performed in sinoaortically denervated rabbits, and similar effects were observed. The effect was specific to the PVN because microinjections of the drugs outside the PVN had no effect on the response. The findings suggest that excitatory inputs into the PVN may be important in the neural responses elicited by elevations in plasma osmolality.

Effects of osmotic changes on the chemoreceptor cell of rat carotid body.

The carotid body plays a crucial role in cardiorespiratory regulation. In the present study we investigated the effect of osmotic changes on cytoplasmic calcium concentration ([Ca(2+)](c)) and pH (pH(i)) of isolated chemoreceptor cells of the rat carotid body. In CO(2)/HCO(3)(-)-buffered medium, reduction of osmolality from the control level of 300 mosmol kg(-1) to 250-285 mosmol kg(-1) resulted in a rise in [Ca(2+)](c), as measured with Indo-1, whereas elevation of osmolality to 350 mosmol kg(-1) had no effect. The Ca(2+) response required extracellular Ca(2+) and was reduced by application of the L-type Ca(2+) channel antagonist nifedipine (10 microM). The hyposmosis-induced Ca(2+) response could be prevented by application of niflumic acid (300 microM), an inhibitor of the swelling-activated Cl(-) channel. In whole-cell patch-clamp experiments niflumic acid abolished the swelling-activated Cl(-) current but only slightly depressed the Ca(2+) current. The inhibition of Ca(2+) current by niflumic acid does not account for its action in preventing of hyposmosis-induced Ca(2+) response, which seems to be initiated by Cl(-)-mediated depolarisation. Withdrawal of CO(2)/HCO(3)(-) also prevented the Ca(2+) response. Reduction of the osmotic concentration by 50 mosmol kg(-1) induced a small but sustained decrease in pH(i), while elevation by 50 mosmol kg(-1) had an inverse effect, as measured fluorimetrically with carboxy SNARF-1. Our conclusion is that in the rat chemoreceptor cell the activation of Cl(-) channels, e.g. by hyposmotic challenge, induces depolarisation, which, in turn, activates voltage-gated Ca(2+) channels.

Protection of Renal Inner Medullary Epithelial Cells from Apoptosis by Hypertonic Stress-induced p53 Activation

Acute hypertonicity causes cell cycle delay and apoptosis in mouse renal inner medullary collecting duct cells (mIMCD3) and increases GADD45 expression. Because the tumor suppressor protein p53 may be involved in these effects, we have investigated the role of p53 in mIMCD3 response to hyperosmotic stress. Acute elevation of osmolality with NaCl addition from the control level of 320 mosmol/kg to 500-600 mosmol/kg greatly increased the levels of total and Ser(15)-phosphorylated p53 within 15 min. However, similar elevation of osmolality with urea did not increase p53 levels. Our studies indicate that induced p53 is transcriptionally active because NaCl addition to 500-600 mosmol/kg stimulated transcription of a luciferase reporter containing a p53 consensus element and appropriately altered mRNA levels of known transcriptional targets of p53, i.e. increased MDM-2 and decreased BCL-2 levels. Elevating NaCl further to 700-800 mosmol/kg rapidly killed most of the cells by apoptosis. At these higher NaCl concentrations, p53 levels were further increased although Ser(15) phosphorylation and transcriptional activity were significantly lower than levels at 500-600 mosmol/kg. At NaCl-induced 500 mosmol/kg, apoptosis was rare in the presence of control, nonspecific oligonucleotide but highly prevalent upon addition of p53 antisense oligonucleotide that substantially reduced p53 levels. We conclude that induction of active p53 in mIMCD3 cells by hypertonic stress contributes to cell survival.

Hemolymph homeostasis in relation to diel feeding activity and microclimate in the prototypal land isopodLigia pallasii

Twenty-four-hour variability in hemolymph osmolality was assessed in a field population of the semiterrestrial isopod Ligia pallasii and related to feeding activity and microenvironmental conditions of relative humidity (RH) and temperature in the species' habitats. Hemolymphs were also analyzed for levels of ammonia and glucose as indicators of digestive and absorptive activities. Comparative data on hemolymph osmolality and microhabitat conditions were also obtained for several ligiid species in Hawai'i. Late-morning peaks in hemolymph osmolality in L. pallasii were coincidental with peaks in ammonia and glucose and with predicted times of digestion/absorption based on observed feeding activity in the population, suggesting that the elevations in osmolality were due to salt-loading from the species' seaweed diet. Uniformity of microenvironmental conditions of RH and temperature in Ligia's supralittoral habitat, whether temperate or tropical, and regardless of time of day or localized weather conditions, suggests that dietary salt-loading is likely the greatest challenge to osmotic homeostasis in ligiids. This feature and other aspects of hemolymph osmolality in ligiids are discussed in the context of colonization of land by prototypal terrestrial isopods.

Hyperosmotic pressure enhances immunoglobulin transcription rates and secretion rates of KR12H-2 transfectoma.

When subjected to hyperosmotic pressure resulting from NaCl addition, KR12H-2 transfectoma, like most hybridomas, displayed a decrease in specific growth rate (mu) and an increase in specific antibody productivity (q(Ab)). Elevation of medium osmolality from 285 to 425 mOsm/kg decreased mu by 20%, while it increased q(Ab) by 376%. Although cell mass also increased at higher osmolality, it was not the main factor in increasing q(Ab). Hyperosmotic pressure was found to enhance transcription levels of immunoglobulin (Ig) mRNAs preferentially, compared with non-IgG mRNA. The transcription levels of both heavy chain (HC) and light chain (LC) mRNAs were enhanced as much as q(Ab). This result suggests that enhanced q(Ab) at higher osmolality was mainly due to enhanced transcription levels of Ig mRNA. However, these increased transcription levels of Ig mRNAs were not due to the enhanced stability of Ig mRNA. In fact, the stability of Ig mRNAs decreased at higher osmolality. Elevation of osmolality from 285 mOsm/kg to 425 mOsm/kg decreased the half-lives of HC and LC mRNAs by 37% and 36%, respectively. A simple mathematical model revealed that transcription rates of Ig mRNAs increased by more than 476% at 425 mOsm/kg. These elevated transcription levels could, in turn, increase the translation rates of Ig polypeptides. However, the translation rates of Ig polypeptides were not enhanced as much as the transcription levels of Ig mRNAs and q(Ab). The elevation of osmolality from 285 mOsm/kg to 425 mOsm/kg increased HC and LC mRNA specific translation rates by 172% and 240%, respectively. Taken together, the data suggest that (1) enhanced q(Ab) of KR12H-2 transfectoma at higher osmolality is due to elevated transcription rates of Ig mRNAs and expedited post-translational processing of Ig, and (2) antibody secretion by KR12H-2 transfectoma is most likely controlled at the level of Ig translation, particularly HC translation.

POSSIBLE MODULATE ANTIDIURETIC HORMONE SECRETION IN RELATION TO CIRCULATING BLOOD VOLUME IN TOTAL ARTIFICIAL HEART IMPLANTED CALVES

Introduction: It has been reported that the circulating blood volume (CBV) increased significantly in total artificial heart (TAH) recipient. Participation of several hormonal factors including antidiuretic hormone (ADH) in this CBV increase has been supposed, yet its detailed mechanism is still unclear. We investigated possible modulation of ADH secretion in TAH recipient in chronic animal experiments. Method: Three calves were implanted with a pneumatic TAH, and the other four calves were implanted only with monitoring lines as controls. After two weeks of postoperative period, two groups were compared in: 1) transition of CBV, plasma ADH level (CADH), and plasma osmolality (Posm), 2) response of CADH to infusion of hyperosmolar saline solution (1M NaCl at 0.1ml/kg/min for 30 min) and to restriction of water intake (2L/day for 3days). Results: The postoperative CBV in a TAH calf significantly increased (130 ± 19 ml/kg), while in the other two TAH calves did not increase (92 ± 13 ml/kg), compared with in control calves (104 ± 19 ml/kg). The postoperative CADH and Posm were within the normal range in all calves (CADH: 1.5 ± 1.0 vs 0.8 ± 0.2 pg/ml, Posm: 273 ± 8 vs 273 ± 7, in TAHs vs controls, respectively). Sensitivity of ADH secretion to Posm elevation in the CBV-increased TAH calf was remarkably suppressed compared with the other, two TAH calves without CBV increase, and the control calves. (0.06 vs 0.55 vs 0.21 pg/ml/mOsm/kg±H2O at hyperosmolar saline infusion, and 0.11 vs. 0.43 vs. 0.55 pg/ml/mOsm/kg±H2O at water intake restriction, respectively). Conclusion: In TAH implanted calves, CBV increases occasionally and the ADH secretion in response to plasma osmolality elevation was modulated concomitantly, these phenomena do not occur consistently.

Hyperosmotic perfusion of the beating rat heart and the role of the Na+/K+/2Cl- co-transporter and the Na+/H+ exchanger.

The aim of the present study was to investigate the role of the Na+/K+/2Cl- co-transporter and the Na+/H+ exchanger on contractile function and electrolyte regulation during hyperosmotic perfusion of the heart. Langendorff perfused rat hearts were subjected to hyperosmolal perfusion in 10-min intervals. Perfusates were made hyperosmotic by adding mannitol to the buffer (370, 450 and 600 mOsmol/kg H2O). Cardiac contractile function was monitored with a balloon in the left ventricle (LV) coupled to a pressure transducer. Cardiac effluent was sampled repeatedly throughout and after hyperosmotic perfusion and analysed for content of Na+, K+, and Cl-. All three hyperosmotic perfusates initially reduced LV developed pressure (LVDP), but for 370 and 450 mOsmol/kg H2O, LVDP recovered to baseline within 4 min of perfusion. With 600 mOsmol/kg H2O, LVDP recovered slowly and was 50% below baseline after 10 min of hyperosmotic perfusion. Inhibition of the Na+/H+ exchanger with 5-(N-ethyl-N-isopropyl) amiloride (EIPA) and 3-methylsulfonyl-4-piperidinobenzoyl-guanidine methanesulfonate (HOE 694) abolished the recovery of LVDP to the 600 mOsmol/kg H2O perfusate, whereas inhibition of the Na+/K+/2Cl- co-transporter had no impact on LVDP. Potassium was taken up by the heart during hyperosmotic perfusion and this uptake was significantly reduced with inhibition of the Na+/H+ exchanger. Intracellular pH was assessed with 31p magnetic resonance spectroscopy and hyperosmolality induced a significant alkalosis that was dependent upon the Na+/H+ exchanger. The rat heart responds to moderate elevations in osmolality with a transient reduction in contractile function, whereas an elevation of 300 mOsmol/kg H2O persistently reduces contractile function. The Na+/H+ exchanger, but not the Na+/K+/2Cl- co-transporter, is of importance in contractile recovery and electrolyte regulation during hyperosmotic perfusion in the rat heart.

Effect of modified carbon allocation on turgor, osmolality, sugar and potassium content, and membrane potential in the epidermis of transgenic potato (Solanum tuberosum L.) plants

The effects of modification in sugar concentrations on turgor pressure and membrane potential in epidermal leaf cells of transgenic potato (Solanum tuberosum cv. Desiree) plants were studied. Measurements of turgor pressure were performed by insertion of a micro pressure probe. Osmolality and sugar concentrations were determined by micro analysis of single cell extracts. Membrane potentials and cell diameters were calculated from repeated, computer-controlled scans with voltage-sensitive microelectrodes. Epidermal cells of sucrose transporter antisense plants showed a more than 100% elevation in osmolality and turgor pressure compared to the wild-type. As a consequence, cell diameters were enhanced in this transgenic line. However, membrane potentials were only slightly reduced in sucrose transporter antisense plants. In addition to sucrose transporter antisense lines, transgenic plants that were reduced in their capacity to accumulate starch due to antisense inhibition of the chloroplastic fructose-1,6-bisphosphatase (FBPase) were investigated. These ahtisense plants maintained membrane potential and turgor pressure comparable to the wild-type.

Effect of modified carbon allocation on turgor, osmolality, sugar and potassium content, and membrane potential in the epidermis of transgenic potato (Solanum tuberosum L.) plants

The effects of modification in sugar concentrations on turgor pressure and membrane potential in epidermal leaf cells of transgenic potato (Solanum tuberosum cv. Desirée) plants were studied. Measurements of turgor pressure were performed by insertion of a micro pressure probe. Osmolality and sugar concentrations were determined by micro analysis of single cell extracts. Membrane potentials and cell diameters were calculated from repeated, computer-controlled scans with voltage-sensitive microelectrodes. Epidermal cells of sucrose transporter antisense plants showed a more than 100% elevation in osmolality and turgor pressure compared to the wild-type. As a consequence, cell diameters were enhanced in this transgenic line. However, membrane potentials were only slightly reduced in sucrose transporter antisense plants. In addition to sucrose transporter antisense lines, transgenic plants that were reduced in their capacity to accumulate starch due to antisense inhibition of the chloroplastic fructose-1,6-bisphosphatase (FBPase) were investigated. These antisense plants maintained membrane potential and turgor pressure comparable to the wild-type.

Serum parameters of Adriatic sturgeon Acipenser naccarii (Pisces: Acipenseriformes): effects of temperature and stress

Data on the concentrations of some blood constituents of captive Adriatic sturgeon, Acipenser naccarii, a primitive bony fish, are reported. Serum osmolality, Na +, K +, Cl −, Ca 2+, cortisol, glucose and total protein concentrations were measured. The effects of anaesthesia, temperature, crowding and prolonged handling stress were tested on a group of 12 4-year-old sturgeons sampled repeatedly. The anaesthetic dose of MS 222 (140 mg l −1) induced significant osmolality elevation in the sturgeon. After exposure to colder temperature (17 versus 25°C), cortisol and Cl − concentrations significantly decreased. The cultured sturgeon did not seem susceptible to crowding and prolonged handling stress, since neither the serum cortisol and glucose levels nor the other blood parameters were affected by these stressors. Results are compared with the few available data on other chondrostean fish and with those on teleosts.

Osmotic Effects upon the Theta Rhythm, a Natural Brain Oscillation in the Hippocampal Slice

Raising plasma osmolality reduces patient susceptibility to generalized tonic-clonic seizure. In brain slices, elevated osmolality reduces epileptiform discharge. Conversely, lowering osmolality can induce generalized tonic-clonic seizure in patients and promotes epileptiform activity in hippocampal or neocortical slices. Rhythmic slow activity or "theta" encodes memory in some mammals and represents n nonpathological oscillation of cortical neurons. In hippocampal slices, theta consists of a 4-10 Hz oscillation overriding a slow depolarization (SD) that recurs periodically. We examined if the theta rhythm, which is a natural brain oscillation, was affected by clinically relevant changes in osmolality. Theta was induced by bath application of 40 μM carbachol and intracellularly recorded in individual CA3 neurons of the rat hippocampal slice. Artificial CSF (ACSF) elevated by 40 milliosmoles (+40 mOsm) using mannitol slowed the SD frequency in 18 of 18 CA3 neurons. Conversely -40 mOsm ACSF increased SD frequency in 12 of 14 neurons. Osmotic alteration did not change theta frequency in 9 of 9 CA3 cells, but overriding action potentials were reduced in number or eliminated by hyperosmotic ACSF in 8 of 12 neurons. Elevation of osmolality with glycerol, which does not alter cell volume, had no effect in 4 of 4 neurons. This indicated that the induced changes in excitability resulted from alterations in cell volume. We examined if osmotically induced changes in cell volume might alter the glial capacity to buffer K+ released by neuronal discharge. Intracellular recordings from glial cells revealed that osmolality had no significant effect upon the glial resting potential itself. In 40 μM carbachol the glial membrane potential slowly oscillated, the depolarizing phase reflecting K+ release by discharging neurons during each SD. Elevating or lowering [K+]o had little effect on SD frequency, indicating that osmotic effects did not act through changes in [K+]o which should result from alterations in the extracellular volume. We conclude that neuronal excitability is osmoresponsive, probably through altered synaptic and field effects. However, the theta rhythm itself is not osmoresponsive.

Effects of intraruminal infusions of sodium acetate and sodium chloride on silage intake by lactating cows

Lactating dairy cows prepared with rumen fistulas were fed on grass silage and concentrates and used in two experiments to compare the effects of sodium acetate and sodium chloride infused over 3 h into the rumen on the voluntary intake of silage. Silage intake was depressed in an approximately linear manner by increasing amounts (6–15 mol) of sodium acetate (NaOAc) and 15 mol NaCl had an effect similar to that of 12 mol NaOAc. Sodium in rumen fluid was significantly correlated with intake as was osmolality. 5.5, 7.4 or 9.1 mol of NaOAc significantly depressed silage intake, while 7.4 and 9.1 mol NaCl had significant effects. There were significant negative relationships between intake and the level of NaOAc or NaCl. It is concluded that the major effect of either salt was via the elevation of osmolality of rumen fluid and the relevance to normal control of feeding is discussed.

Pathophysiology of Inner Ear Fluid Imbalance

Maintenance of homeostasis of inner ear fluids and biochemical integrity of inner ear tissue are essential for proper functioning of the auditory and vestibular end organs. Although various regulatory mechanisms exist in a different portion of the labyrinth, the inner ear is known to respond to systemic challenges. The association of Meniere's syndrome with an imbalance of inner ear fluid homeostasis has been hypothesized for the past century. Among many factors, the effects of hormonal imbalance on inner ear fluid composition and inner ear function have however scarcely been studied. The purpose of this study was to explore the relationship between the autonomic nervous system and inner ear function and possible mechanisms of functional disturbances in an experimental condition. An infusion of supraphysiologic amounts of epinephrine, a stress related hormone, resulted in an elevation of osmolality in serum and perilymph. Furthermore, the infusion of epinephrine resulted in elevation of threshold, prolongation of latency, and depression of amplitude in the compound action potential of the auditory nerve. These findings were most marked at high frequencies. We hypothesized that the epinephrine-induced hearing loss was brought about by an increase in perilymphatic osmolality, as well as by the ionic imbalance caused by the osmotic gradient. Since emotional stress has been implicated as a mechanism of inducing a Meniere's attack, evaluation of the relationship between the autonomic system and cochlear function may contribute to the understanding of possible mechanisms of inner ear dysfunction caused by hormonal imbalances.

Hyperosmotic mannitol and collateral blood flow to ischemic myocardium

Elevation of extracellular osmolality reduces the extent of myocardial and endothelial cell swelling that accompanies acute ischemia, and the reduction of cell swelling is associated with an increase in collateral blood flow to the ischemic area. However, little is known about the effects of hyperosmolality on the vascular resistance of the collateral coronary vasculature. We compared the effects of hyperosmolar mannitol with those of nitroglycerin and dipyridamole on the vascular resistance of large collateral coronary vessels and of the small arterial vasculature in an isolated heart model of regional ischemia. Elevation of osmolality by mannitol increased collateral blood flow to the ischemic region through at least two mechanisms. First, increasing osmolality resulted in dilation of large arterial conductance vessels, similar to that produced by nitroglycerin. In addition, mannitol produced an effect on the coronary circulation at a microvascular level which, per se or in combination with its effect on larger collateral conductance vessels, increased collateral blood flow to ischemic regions.