An evaluation of the membrane constants and the potassium conductance in metabolically exhausted muscle fibres.

Abstract

The membrane characteristics of metabolically poisoned and mechanically exhausted frog skeletal muscle fibers were investigated with intracellular micro-electrodes. When CN- plus iodoacetate were applied as metabolic poisons twitch tension declined towards 0 after 150-300 stimuli (0.3 Hz; 0.degree. C). At the beginning of stimulation the mean resting potential fell from -75 to -69 mV; it rose subsequently to -83 mV. The membrane resistance decreased during this stimulation period along a sigmoid time course to 4-6% of the original value. In completely exhausted fibers the following membrane constants were estimated (23.degree. C): length contant, 0.31 mm; input resistance, 31 k.OMEGA.; membrane resistance 58 .OMEGA.cm2. In metabolically exhausted muscle fibers the surface and tubular membranes were still intact and the observed decrease in membrane resistance was mainly due to an increase K conductance. The gating mechanism of the K channels (presumably those with the characteristics of the slow component) were affected when energy reserves diminished.