Correlation of the effect of Ca+2 on Na+ and K+ permeability and membrane potential of Ehrlich ascites tumor cells

✍ Scribed by Thomas C. Smith; Kim D. Vernon

• Publisher: John Wiley and Sons
• Year: 1979
• Tongue: English
• Weight: 855 KB
• Volume: 98
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1040980212

✦ Synopsis

Abstract

The effect of Ca^+2^ on the transport and intracellular distribution of Na^+^ and K^+^ in Ehrlich ascites tumor cells was investigated in an effort to establish the mechanism of Ca^+2^‐induced hyperpolarization of the cell membrane. Inclusion of Ca^+2^ (2mM) in the incubation medium leads to reduced cytoplasmic concentrations of Na^+^, K^+^ and Cl^−^ in steady state cells. In cells inhibited by ouabain, Ca^+2^ causes a 41% decrease in the rate of net K^+^ loss, but is without effect on the rate of net Na^+^ accumulation. Net K^+^ flux is reduced by 50%, while net Na^+^ flux is unchanged in the transport‐inhibited cells. The membrane potential of cells in Ca^+2^‐free medium (‐13.9 ± 0.8 mV) is unaffected by the addition of ouabain. However, the potential of cells in Ca^+2^‐containing medium (‐23.3 ± 1.2 mV) declines in one hour after the addition of ouabain to values comparable to those of control cells (‐15.2 ± 0.7 mV).

The results of these experiment are consistent with the postulation that Ca^+2^ exerts two effects on Na^+^ and K^+^ transport. First, Ca^+2^ reduces the membrane permeability to K^+^ by 25%. Second, Ca^+2^ alters the coupling of the Na/K active transport mechanism leding to an electrogenic hyperpolarization of the membrane.