[Effect of the medium composition on the resting membrane potential in the earthworm longitudinal somatic muscle fibers].

Norepinephrine or increased extracellular K+ hyperpolarize the membrane of the earthworm somatic muscle fibre, whereas removal of Cl- from external solution or a hypotonic solution depolarize the membrane. The dependence of the membrane resting potential on the extracellular K+ is quite characteristic against the background of ouabain action. A preliminary membrane depolarisation by ouabain eliminates the above effects on the membrane resting potential. The data obtained suggest that the ouabain-sensitive active ion pump directly contributes to the membrane resting potential value. This hypothesis is discussed with respect to existence of active Cl- transport combined with Na+, K(+)-pump which presumably takes part in the intracellular osmotic pressure regulation in the earthworm somatic muscle.