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
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