Osmotic adjustment in an estuarine population of Urosalpinx cinerea (Say, 1822) (Muricidae, Gastropoda).
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Individuals from a subtidal, estuarine population of the common oyster drill, Urosalpinx cinerea (Say, 1822), were brought into the laboratory and tested for osmotic adjustment to changing salinity. Tissue variables monitored at seven experimental salinities ranging from 10 to 40% were tissue fluid osmolality, chloride, sodium, potassium, free amino acids (FAA), ninhydrin-positive substances (NPS) and water content. The results of this study demonstrate that the test animals did not exhibit anisosmotic regulation at any of the experimental salinities. However, the data do suggest a high degree of hyper-ionic regulation of potassium at all experimental salinities and a hyporegulation of sodium between the 25 and 40% salinities. Taurine, aspartic acid, alanine and glycine were the four FAA present in relatively consistent high amounts. These four amino acids comprised from 59.6 to 75.7% of the total FAA pools. It is postulated that the population does not maintain its euryhaline survival status through an osmoregulatory mechanism. Rather, the population has probably adapted physiologically to withstand dilution of its body fluids during spring conditions of low salinities. (+info)
Assay of intercellular adhesiveness using cell-coated Sephadex beads as collecting particles.
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A simple, rapid and precise method, based on a previous method, for measuring relative rates of intercellular adhesion is described. DEAE-Sephadex beads were treated with nitrocellulose in order to allow cells to grow on their surfaces. Balb/c 3T3 and Balb/c 3T12 cells were used to characterize the assay. They formed confluent cell layers on nitrocellulose-treated DEAE-Sephadex. These cell-coated beads were employed to collect 32P-labelled cells from single cell suspensions. Since they formed statistically uniform, large collecting surfaces, the collection of labelled cells was markedly improved as compared to the original assay. The cell-coated beads collected a large percentage of the labelled cells in a short time. The percentage of cells collected was independent of the concentration of labelled cells in the assay mixture, and the collection was linear for approximately 60 min. The variability between replicate assays was usually +/- 5%. The assay allows the rapid and precise determination of intercellular adhesion in large numbers of individual samples. These features make it useful to screen for effects of different treatments on intercellular adhesions. (+info)
Influence of the sodium pump on intercellular communication in heart fibres: effect of intracellular injection of sodium ion on electrical coupling.
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1. The effect of intracellular sodium injection on the electrical coupling between cardiac Purkinje cells was investigated. 2. It was found that an increase in the intracellular sodium concentration produces uncoupling in about 500 sec and increases the input resistance of the injected cell. Both effects were completely reversible. 3. Inhibition of the sodium pump by ouabain (6-8 x 10(7) M) also causes electrical uncoupling. 4. The decoupling of heart cells achieved by sodium injection was considerably accelerated in fibres treated with ouabain. 5. The influence of sodium injection on cell communication seems to be related to the intracellular calcium concentration 6. The above results indicate that the maintenance of a low intracellular sodium concentration by the sodium pump is essential for the preservation of a high junctional conductance in cardiac fibres. (+info)
Regulation of intracellular chloride by cotransporters in developing lateral superior olive neurons.
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The regulatory mechanisms of intracellular Cl- concentration ([Cl-]i) were investigated in the lateral superior olive (LSO) neurons of various developmental stages by taking advantage of gramicidin perforated patch recording mode, which enables neuronal [Cl-]i measurement. Responses to glycine changed from depolarization to hyperpolarization during the second week after birth, resulting from [Cl-]i decrease. Furosemide equally altered the [Cl-]i of both immature and mature LSO neurons, indicating substantial contributions of furosemide-sensitive intracellular Cl- regulators; i.e., K+-Cl- cotransporter (KCC) and Na+-K+-Cl- cotransporter (NKCC), throughout this early development. Increase of extracellular K+ concentration and replacement of intracellular K+ with Cs+ resulted in [Cl-]i elevation at postnatal days 13-15 (P13-P15), but not at P0-P2, indicating that the mechanism of neuronal Cl- extrusion is sensitive to both furosemide and K+-gradient and poorly developed in immature LSO neurons. In addition, removal of extracellular Na+ decreased [Cl-]i at P0-P2, suggesting the existence of extracellular Na+-dependent and furosemide-sensitive Cl- accumulation in immature LSO neurons. These data show clearly that developmental changes of Cl- cotransporters alter [Cl-]i and are responsible for the switch from the neonatal Cl- efflux to the mature Cl- influx in LSO neurons. Such maturational changes in Cl- cotransporters might have the important functional roles for glycinergic and GABAergic synaptic transmission and the broader implications for LSO and auditory development. (+info)
Effects of phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-phosphate on a Na+-gated nonselective cation channel.
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Olfactory receptor neurons in the lobster express a nonselective cation channel that is activated by intracellular Na+ and carries a substantial part of the depolarizing receptor current. Here, we show that phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] and phosphatidylinositol 4-phosphate [PI(4)P] applied to the intracellular face of cell-free patches activate the channel in the absence of Na+ and that antibodies against the respective phospholipids irreversibly inhibit the evoked activity. Further, we show that applying PI(4,5)P2 or PI(4)P in the presence of Na+ decreases the concentration of Na+ required to activate the channel from an EC50 of 74 to 22 mM for PI(4,5)P2 and to 29 mM for PI(4)P, respectively. Na+-gated channel activity was irreversibly inhibited by monoclonal antibodies against PI(4,5)P2 and PI(4)P in patches never exposed to exogenous phosphatidylinositols, suggesting that endogenous inositol phospholipids are required for the activation of the channel by intracellular Na+. Our findings suggest that PI(4,5)P2 and/or PI(4)P may serve as intracellular signaling molecules in these primary sensory neurons and provide a general mechanism to explain how the sensitivity of Na+-gated channels to Na+ could be much greater in intact cells than in excised membrane patches. (+info)
The systemic and renal response to NO inhibition is not modified by angiotensin-II-receptor blockade in healthy humans.
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BACKGROUND: The role of angiotensin II (Ang II) in the systemic and renal responses to acute nitric oxide (NO) synthesis inhibition has not been studied in detail in healthy humans. The purpose of the present study was to investigate the effects of Ang II receptor blockade on the systemic and renal response to acute treat ment with Ng-monomethyl-L-arginine (L-NMMA) in healthy subjects. METHODS: Mean arterial blood pressure (MAP), renal plasma flow (RPF), glomerular filtration rate (GFR), sodium excretion (UNa*V), and plasma levels of renin, Ang II, ANP, BNP, and cGMP were assessed in 15 healthy sodium replete humans before and after acute L-NMMA treatment (3 mg/kg) on two occasions, i.e. after pretreatment with the Ang II type 1 receptor (AT-1) antagonist candesartan cilexetil (CAND; 8 mg) or placebo in a double blind, randomized fashion. Renal haemodynamics were measured during water diuresis using renal clearances of [125I]hippuran and [51Cr]EDTA. Plasma hormones were measured by radioimmunoassays. RESULTS: On both study days L-NMMA treatment induced a significant increase in MAP and a significant decrease in GFR, RPF, and UNa*V. These effects of L-NMMA were not affected significantly by pretreatment with CAND. The effects of L-NMMA on hormones were roughly similar on both occasions with a drop in P-cGMP and U-cGMP. However, a fall in renin was observed only during CAND pretreatment. CONCLUSIONS: We conclude that Ang II is not a major mediator of acute vasoconstriction and sodium retention during acute lowering of NO activity in healthy man. (+info)
Augmentation of diabetes-associated renal hyperfiltration and nitric oxide production by pregnancy in rats.
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We tested the hypothesis that pregnancy might increase diabetes-associated nitric oxide (NO) production and renal hyperfiltration. Two weeks following i.v. streptozotocin (40 mg/kg), mean arterial pressure (MAP) was not modified by diabetes; glomerular filtration rate (GFR), renal plasma flow (RPF) and filtration fraction (FF) were higher in pregnant than in virgin controls and increased by diabetes to a greater extent in pregnant than in virgin rats. Urinary volume (UV), creatinine, albumin and sodium (UNaV) were significantly increased by diabetes. Diabetes led to an increase in renal, cardiac, aortic and uterine but not in placental NO synthase activities. Infusion of NG-nitro-l-arginine (l-NA) caused a dose-dependent reduction in GFR, RPF, plasma NO2-/NO3-, UV and UNaV; in general, diabetes increased these effects to a greater extent in pregnant than in virgin rats. l-NA increased MAP in all groups of rats but did not alter FF. Diabetes did not alter responses of thoracic aorta rings to vasoconstrictor effects of phenylephrine and the vasorelaxant effects of sodium nitroprusside but increased endothelium-dependent relaxant effects of acetylcholine. In general the effects of diabetes of 7 days duration were similar to those described above for diabetes of 14 days duration. These data suggest that diabetes-associated renal hyperfiltration and NO production are augmented by pregnancy. (+info)
NMDA receptor-mediated K+ efflux and neuronal apoptosis.
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Neuronal death induced by activating N-methyl-D-aspartate (NMDA) receptors has been linked to Ca2+ and Na+ influx through associated channels. Whole-cell recording from cultured mouse cortical neurons revealed a NMDA-evoked outward current, INMDA-K, carried by K+ efflux at membrane potentials positive to -86 millivolts. Cortical neurons exposed to NMDA in medium containing reduced Na+ and Ca2+ (as found in ischemic brain tissue) lost substantial intracellular K+ and underwent apoptosis. Both K+ loss and apoptosis were attenuated by increasing extracellular K+, even when voltage-gated Ca2+ channels were blocked. Thus NMDA receptor-mediated K+ efflux may contribute to neuronal apoptosis after brain ischemia. (+info)