Effects of methylene blue and ascorbate on transmembrane potential in frog skeletal muscle.
1. The effects of methylene blue (MB, 10(-4) M) and ascorbate (ASC, 10(-4) M) on the resting membrane potential of frog skeletal muscle fibers were studied in Cl(-)-free medium at various external K+ concentrations. 2. Muscle fibers formed two distinct populations according to their resting potentials (hyperpolarized to -104 mV or depolarized to -31 mV) after a 90 min period of K+ withdrawal. ASC increased the relative contribution of hyperpolarized fibers, while in the presence of MB, all fibers depolarized during the 90 min of K+ withdrawal. 3. In the presence of 2.5 mM K+, ASC had no significant effect on the resting potential, while MB moved half of the fibers into the depolarized pool. Elevation of [K+]0 to 10 mM caused repolarization of all previously depolarized fibers (to -63 mV) in spite of the continuous presence of MB. 4. Ionic currents were measured during a 60 mV depolarization step using the double sucrose-gap technique. MB significantly increased the peak inward current, while ASC had no effect. The steady-state outward current was not affected by MB or ASC. 5. The results suggest that ionic conductances may be under redox control in frog skeletal muscle.
Nánási
P P
PP
Department of Physiology, University Medical School of Debrecen, Hungary.
Dely
M
M
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D004594:Electrophysiology; D007473:Ion Channels / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects*; D008751:Methylene Blue / Q000494:pharmacology*; D018482:Muscle, Skeletal / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D011893:Rana esculenta; D051381:Rats
D007473:Ion Channels; D001205:Ascorbic Acid; D011188:Potassium; D008751:Methylene Blue