THE CONTROL OF THE MEMBRANE POTENTIAL OF MUSCLE FIBERS BY THE SODIUM PUMP. (25/218)

Frog sartorius muscles were made Na-rich by immersion in K-free sulfate Ringer's solution in the cold. The muscles were then loaded with Na(24) and the extracellular space cleared of radioactivity. When such Na-rich muscles were transferred to lithium sulfate Ringer's solution at 20 degrees C, Na efflux was observed to increase with time, to reach a maximum about 15 minutes after the transfer of the muscles to Li(2)SO(4), and then to decline. The decline in efflux from these muscles was proportional to ([Na](i))(8) over a considerable range of [Na](i). The membrane potential of Na-rich muscles was about -48 mv in K-free sulfate Ringer's at 4 degrees C but changed to -76 mv in the same solution at 20 degrees C and to -98 mv in Li(2)SO(4) Ringer's at 20 degrees C. By contrast, muscles with a normal [Na](i) showed a fall in membrane potential when transferred from K-free sulfate Ringer's to Li(2)SO(4) Ringer's solution. The general conclusions from this study are (a) that Na extrusion is capable of generating an electrical potential, and (b) that increases in [Na](i) lead to reversible increases in P(Na) of muscle fibers.  (+info)

MOVEMENTS OF RADIOACTIVE SODIUM IN CEREBRAL-CORTEX SLICES IN RESPONSE TO ELECTRICAL STIMULATION. (26/218)

1. Sodium exchange was measured with (24)Na in incubated guinea-pig cerebral-cortex slices maintained under adequate metabolic conditions with a steady content of fluid and ions resembling that of brain in vivo. 2. Evidence was obtained indicating that Na(+) ions behaved in the inulin space as if they were extracellular, and that their entry into the non-inulin space of unstimulated tissue was about 10 times slower and could be separated, on the basis of complete exchangeability, into two components, a ;fast' one, which reacted to electrical stimulation, and a ;slow' one, exchanging at a rate of about 8muequiv./g./hr., which was not affected by stimulation. 3. The average rate of sodium turnover in unstimulated slices was 175-275muequiv./g./hr., whereas that for stimulated slices was approx. 4-6 times this, or 1050-1180muequiv./g./hr. The stimulated rate was equivalent to a turnover of 32% of the sodium in the non-inulin space/min., or 3mmuequiv./g./impulse. 4. Response to the onset of stimulation appeared to be immediate, but after cessation of stimulation increased sodium movements persisted for several minutes before return to unstimulated values. 5. Calculations based on electrochemical gradients suggested that about one-quarter of the energy available from respiration was required for sodium and potassium transport at maximal rates in both unstimulated and stimulated cerebral-cortex slices.  (+info)

Membrane-permeabilizing activities of amphidinol 3, polyene-polyhydroxy antifungal from a marine dinoflagellate. (27/218)

Amphidinols, which are polyene-polyhydroxy metabolites produced by the marine dinoflagellate Amphidinium klebsii, possess potent antifungal and hemolytic activities. The membrane permeabilizing actions of amphidinol 3, the most potent homologue, were compared with those of polyene antibiotics, amphotericin B (AmB) and filipin, in hemolytic tests, 23Na nuclear magnetic resonance (NMR)-based membrane permeabilizing assays, and UV spectroscopy for liposome-bound forms. In Na+ flux experiments using large unilamellar vesicles (LUVs), ion efflux by amphidinol 3 was inhibited by cholesterol or ergosterol, which was opposed to previous results [J. Mar. Biotechnol., 5 (1997) 124]. When the effect of the agents on the size of vesicles was examined by light scattering experiments, amphidinol 3 did not significantly alter their size while filipin and synthetic detergent Triton X-100 did. The observations implied that the activity of amphidinol 3 was mainly due to formation of large pores/lesions in liposomes rather than detergent-like disruption of membrane. The pore/lesion size was estimated to be 2.0-2.9 nm in diameter on the basis of osmotic protection experiments using blood cells. The UV spectra in liposomes, which revealed the close interaction of polyene moieties in a lipid bilayer, further implied that the membrane activity of amphidinol 3 is caused by the molecular assemblage formed in biomembrane. These results disclose that amphidinol 3 is one of few non-ionic compounds that possess potent membrane permeabilizing activity with non-detergent mechanism.  (+info)

Analysis of unidirectional fluxes of sodium during diarrhea induced by Clostridium perfringens enterotoxin in the rat terminal ileum. (28/218)

Net intestinal transport of sodium in vivo, in control and enterotoxin (Clostridium perfringens)-treated rats, was resolved into two unidirectional fluxes, influx from and efflux into the lumen of the terminal ileum. In rats treated with the toxin, sodium influx remained similar to control values even during fluid and electrolyte loss to the lumen. Net loss of sodium was shown to be due to nearly a twofold increase in sodium efflux to the lumen in toxin-treated animals. There was only slight histopathological damage to the mucosa, especially noticeable at the tips of villi.  (+info)

Active chloride secretion by in vitro guinea-pig seminal vesicle and its possible relation to vesicular function in vivo. (29/218)

1. The guinea-pig seminal vesicle in vivo is characterized by a transmural electrical potential difference of approximately 11 mV with the lumen electrically negative with respect to the interstitial fluid. The concentrations of Na, Cl and K in the vesicular fluid are 13, 15, and 0-4 mM, respectively. 2. When mounted as a flat sheet in a short-circuit apparatus, guinea-pig seminal vesicles initially undergo a decline in the transmural electrical potential difference and short-circuit current ('low phase') followed by a spontaneous increase in these parameters ('high phase'). 3. During the low phase, net C1 movements across the tissue do not differ significantly from zero, and there is a small 'residual' current that is unaccounted for. 4. During the high phase, there is a significant active C1 secretion into the mucosal solution, not detectable net movement of Na and an unaccounted for or 'residual' current that is equal to that found in the low phase. 5. Theophylline, dibutyryl-3'-5' cyclic adenosinemonophosphate,prostaglandin E1 and prostaglandin F2alpha markedly stimulate the transmural electrical potential difference and short-circuit current during the low phase, but have no effect when added to the bathing solution during the high phase. 6. Diffusion potentials determined across in vitro seminal vesicles suggest that the spontaneous transmural electrical potential difference in vivo may be attributable to the large ionic asymmetries between the vesicular fluid and the plasma. 7. It is postulated that two phases are involved in the elaboration of seminal vesicular fluid. The initial phase, following emptying of the vesicle, is characterized by the secretion of electrolytes, organic molecules and water. Active C1 secretion presumably regulated by intracellular cyclic adenosinemonophosphate and/or prostaglandins may be the driving force for this initial secretion of electrolytes. Following this secretory phase, electrolytes and water are reabsorbed, thereby concentrating the organic components in the vesicular reservoir.  (+info)

Low-grade glioma: correlation of short echo time 1H-MR spectroscopy with 23Na MR imaging. (30/218)

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Tissue sodium concentration in myocardial infarction in humans: a quantitative 23Na MR imaging study. (31/218)

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The application of 23Na double-quantum-filter (DQF) NMR spectroscopy for the study of spinal disc degeneration. (32/218)

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