PHYSIOLOGICAL DEVELOPMENT OF ACETYLCHOLINE RECEPTORS IN EMBRYONIC XENOPUS MUSCLE CELLS IN CULTURE (PATCH CLAMP)

The physiological properties of acetylcholine receptors (AChRs) in embryonic skeletal muscle cells were studied during very early stages of development. The technique of patch-clamp single channel recording was used to record the currents flowing through individual membrane receptor channels activated by acetylcholine. Recordings were made from muscle cells as early as stage 20, the stage at which AChRs first emerge at the muscle surface. The properties of receptors at such early stages were compared with those of receptors in more mature myocytes. It was found that the muscle cells exhibited two classes of AChRs at all developmental stages studied, but that the relative proportions of the two classes changed during development. Early stage muscles contained mainly small (25 pS) conductance channels, and relatively few large (42 pS) conductance channels. During development the proportion of large conductance channels increased steadily. Most physiological properties of the individual receptor classes did not appear to change during development, with the striking exception of the mean open time of the small conductance channels, which underwent a four-fold reduction between developmental stages 21 and 48 (3 to 4 days in culture). The mean open time of the large conductance channels, however, did not show such a decrease. Some of these results have appeared previously in published form.('(1,2))