Acetylcholine-Induced Current in Perfused Rat Myoballs

I N T R O D U C T I O N Acetylcholine (ACh) acts on the endplate of striated muscle by opening a large, water-filled pore which is selectively permeable to cations (Maeno et al., 1977; Huang et al., 1978; Dwyer et al., 1979). Attempts to understand the details of permeation have been hampered by the inability to control or even determine the ionic composition of the intracellular milieu. For example, measurement of ACh currents at very depolarized potentials is made difficult by the presence of large voltage-activated K currents. The K channel cannot be blocked simply with extracellular te t raethylammonium (TEA) because TEA also interacts strongly with the ACh channel (Adler et al., 1979). If the intracellular K could be replaced by a cation which is impermeable through the K channel, this difficulty would be alleviated. Another difficulty that is encountered in traditional studies of the motor endplate is the inability to test J. GEN. PHYSIOL. ~)The Rockefeller University Press 9 0022-1295/80/03/0297/25 $1.00 297 Volume 75 March 1980 297-321 on Jne 4, 2017 D ow nladed fom Published March 1, 1980