Physiol. Res. 49: 481-484, 2000

RAPID COMMUNICATION

Participation of Electrogenic Na+-K+-ATPase in the Membrane Potential of Earthworm Body Wall Muscles

E. M. Volkov1, L. F. Nurullin1, I. Švandová2,3, E. E. Nikolsky1,4, F. Vyskočil2,3

1State Medical University, Kazan, Russia, 2Institute of Physiology, Czech Academy of Sciences, 3Department of Animal Physiology and Developmental Biology, Charles University, Czech Republic and 4Institute of Biochemistry and Biophysics, Russian Academy of Sciences, Kazan, Russia

Received May 4, 2000
Accepted June 5, 2000


Summary
The effect of Na+-K+-ATPase inhibitor ouabain on the resting membrane potential (Vm) was studied by glass microelectrodes in isolated somatic longitudinal muscles of the earthworm Lumbricus terrestris and compared with frog sartorius muscle. In earthworm muscle, Vm was –49 mV (inside negative) in a reference external solution with 4 mmol/l K+. The electrogenic participation of Na+-K+-ATPase was absent in solutions with very low concentrations of 0.01 mmol/l K+, higher in 4 and 8 mmol/l K+ (4-5 mV) and maximal (13 mV) in solutions containing 12 mmol/l K+ where Vm was –46 mV in the absence and –33 mV in the presence of 1x10-4 M ouabain. The electrogenic participation of Na+-K+-ATPase was much smaller in m. sartorius of the frog Rana temporaria bathed in 8 and 12 mmol/l K+. The results indicate that the Na+-K+-ATPase is an important electrogenic factor in earthworm longitudinal muscle fibres and that its contribution to Vm depends directly on the concentration of K+ in the bathing solution.


Key words
Na+-K+-ATPase · Resting membrane potential · Ouabain · Earthworm · Frog

Reprint requests
F. Vyskočil, Institute of Physiology, Academy of Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague 4, Czech Republic. E-mail: vyskocil@biomed.cas.cz


© 2000 by the Institute of Physiology, Czech Academy of Sciences