Chloride Cotransport in the Membrane of Earthworm Body Wall Muscles

E. M. VOLKOV¹, L. F. NURULLIN¹, E. NIKOLSKY^1,4, J. KRŮŠEK,
F. VYSKOČIL<sup>2,3

1</sup>State Medical University, Kazan, Russia, ²Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, 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 11, 2001
Accepted October 15, 2002

Summary
The resting membrane potential (Vm) of isolated somatic longitudinal muscles of the earthworm Lumbricus terrestris was studied by glass microelectrodes. The inhibition of chloride permeability by low pH did not affect Vm of the muscle fibers in isolated somatic longitudinal muscles of the earthworm Lumbricus terrestris which was –48.7 mV (inside negative) at pH 7.3 and –49.1 at pH 5.6. On the other hand, bathing the muscles in Cl- and Na+-free solutions, or application of the chloride transporter inhibitor furosemide and Na+-K+-ATPase inhibitor ouabain depolarized the Vm by 3-5 mV. The effects of a Cl- -free solution and ouabain were not additive. This demonstrates relatively small contribution of equilibrium potential for Cl- to the resting membrane potential and electrogenic effect of Na+K+-ATPase which is dependent on the supply of Na+i ions by furosemide-sensitive and Cl-e- and Na+e-dependent electroneutral transport (most probably Na+K+Cl- cotransport).

Key words
Earthworm • Resting membrane potential • Na+-K+-ATPase • Ouabain • Furosemide • Chloride transporter

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