The Journal of General Physiology
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The Journal of General Physiology, Vol 52, 424-443, Copyright © 1968 by The Rockefeller University Press

ARTICLE

Net Uptake of Potassium in Neurospora Exchange for sodium and hydrogen ions

Clifford L. Slayman 1 and Carolyn W. Slayman 1

1 From the Departments of Physiology and Biology, Western Reserve University, Cleveland, Ohio 44106.

The present address of both authors is Departments of Physiology and Microbiology, Yale University School of Medicine, New Haven, Connecticut 06510

Net uptake of potassium by low K, high Na cells of Neurospora at pH 5.8 is accompanied by net extrusion of sodium and hydrogen ions. The amount of potassium taken up by the cells is matched by the sum of sodium and hydrogen ions lost, under a variety of conditions: prolonged preincubation, partial respiratory inhibition (DNP), and lowered [K]o. All three fluxes are exponential with time and obey Michaelis kinetics as functions of [K]o. The Vmax for net potassium uptake, 22.7 mmoles/kg cell water/min, is very close to that for K/K exchange reported previously (20 mmoles/kg cell water/min). However, the apparent Km for net potassium uptake, 11.8 mM [K]o, is an order of magnitude larger than the value (1 mM) for K/K exchange. It is suggested that a single transport system handles both net K uptake and K/K exchange, but that the affinity of the external site for potassium is influenced by the species of ion being extruded.

Submitted on April 22, 1968


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