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Journal of Experimental Biology 93,81-92 (1981)
Published by Company of Biologists 1981

Turnover of Monovalent Cations in Paramecium

HELEN G. HANSMA ¹

¹ Department of Biological Sciences, University of California, Santa Barbara, California 93106

Regulation of sodium and potassium by Paramecium was studied by measuring fluxes of ²²Na and ⁸⁶Rb respectively. Fluxes of these tracers had the following similarities. (1) Steady-state turnover showed approximately single-pool kinetics with 50% turnover in h. (2) Efflux of both cations showed a specific exchange diffusion when the medium contained the corresponding non-radioactive cation. (3) The net efflux of both cations was slow in the absence of exchange diffusion.

Fluxes showed the following differences. (1) The cells had 2 to 4 times as much K+Rb as Na. Therefore, (2) the K+Rb fluxes at steady state were 2-4 times larger than the Na fluxes, since the fractional turnover was the same for both cations. (3) Membrane excitation by Ba²⁺ stimulated the efflux of Rb but not Na. The efflux of ⁸⁶Rb during membrane excitation appeared to represent the outward or delayed rectification that repolarizes the membranes after an action potential, since it was absent in a pawn mutant that is lacking in membrane excitation.