Influence of sodium pump and Na(+), K(+), CL(-)-cotransport on the resting membrane potential of somatic muscle cells of the earthworm Lumbricus terrestris]

Tetrodotoxin and acidic pH do not change the resting membrane potential (RMP), whereas Na+ or Cl- free solutions or ouabain and furosemide equally depolarize the membrane of the earthworm somatic muscle cells. The findings of the RMP depending on extracellular K+ concentration corroborate theoretical model by Goldman-Hodgkin-Katz only in Na(+)-free medium or in presence of ouabain. The data suggest that the RMP is the sum of potassium and chlorine diffusion potentials as well as of the potential produced by electrogenic component of Na+ pump and, probably, by furosemide-sensitive Na+,K+Cl- co-transport.