Physiological role of desensitized cholinoceptors in skeletal muscle

Abstract

The effect of desensitized cholinoceptors on the time course of end-plate currents was evaluated in frog skeletal muscle at a high (physiological) level of acetylcholine secretion in the presence of active acetylcholinesterase, with two-electrode recording of the membrane potential. When the number of cholinoceptors was small so that they did not appreciably affect the amplitude of end-plate currents or the parameters of onequantum responses (miniature currents), the decay of multiquantum currents was significantly accelerated. Moreover, the presence of cholinoceptors drastically reduced the ability of acetylcholinesterase inhibitors to prolong the decay of end-plate currents. It is suggested that desensitized cholinoceptors in a synapse with a physiological level of acetylcholine secretion and active acetylcholinesterase may bind free acetylcholine with high affinity and thus supplement the well-known physiological role of acetylcholinesterase in limiting the reactivation of postsynaptic membrane cholinoceptors