The Control of the Membrane Potential of Muscle Fibers by the Sodium Pump |
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Authors: | L. J. Mullins and M. Z. Awad |
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Affiliation: | From the Department of Biophysics, University of Maryland School of Medicine, Baltimore |
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Abstract: | 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 Na24 and the extracellular space cleared of radioactivity. When such Na-rich muscles were transferred to lithium sulfate Ringer's solution at 20°C, Na efflux was observed to increase with time, to reach a maximum about 15 minutes after the transfer of the muscles to Li2SO4, 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°C but changed to -76 mv in the same solution at 20°C and to -98 mv in Li2SO4 Ringer's at 20°C. By contrast, muscles with a normal [Na]i showed a fall in membrane potential when transferred from K-free sulfate Ringer's to Li2SO4 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 PNa of muscle fibers. |
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