Effect of phlorizin on the changes of membrane potential, water, Na and K transport induced by cevadine in frog muscle.

The effect of phlorizin on the parameters of cevadine induced membrane potential oscillation and the development of the potential changes were investigated in frog (Rana esculenta) sartorius muscles. The action of phlorizin on Na transport, water and cation contents of cevadine-treated muscles were also studied. On the effect of phlorizin applied at a concentration of 1 mmol/1 the frequency of the membrane potential oscillation evoked by cevadine decreased by about half, parallel with an about four-fold increase in the duration of the resting period and the prepotential. Phlorizin, applied at a concentration of 2 mmol/l on the neural part of the muscle before cevadine treatment, delayed the development of depolarization evoked by cevadine. In the cevadine-pretreated muscles the enhanced 24Na-uptake was not reduced by 2 mmol/l phlorizin. 2 mmol/l phlorizin, applied during the radioactivity washout period, diminished reversibly the rate coefficient for 24Na loss by 49% in 120 min. The 24Na-efflux increasing effect of cevadine, which is characteristic otherwise, was prevented by phlorizin. This action was also reversible. The intracellular water, Na, and K contents of muscles were not altered significantly by 2 mmol/l phlorizin even in 3 hours. Under the effect of cevadine the characteristic gain in intracellular water, Na content and [Na]i developed despite phlorizin treatment, but the changes mentioned above evolved more slowly. In the phlorizin-pretreated muscles the K-content decreasing effect of cevadine failed to come about. In the muscles pretreated with phlorizin the [K]i was reduced by cevadine at a proportional degree to water-uptake.