DEVELOPMENT OF NICOTINIC ACETYLCHOLINE RECEPTOR FUNCTION.

The biophysical properties of acetylcholine receptor (AChR) channels were studied in vivo in developing myotomal muscle of the amphibian, Xenopus laevis. Single-channel recordings from nonjunctional membrane revealed a class of low-conductance (37 pS), long-open-time (2 to 3 msec) AChR channels which appeared on embryonic membrane within 21 hr. of fertilization. At 45 hr. of age, a second class of higher-conductance (57 pS), brief-open-time (0. 7 msec) channels began to be expressed and, over the course of four days, became the most frequently observed channel type on the nonjunctional membrane. Activity of this channel was also predominant at junctional regions of mature myotomal muscle.