PROPERTIES OF ACETYLCHOLINE-RECEPTORS IN ADULT-RAT SKELETAL-MUSCLE FIBERS IN CULTURE

The distribution and biophysical properties of acetylcholine receptors were studied, using morphological and patch-clamp techniques, in adul t rat skeletal muscle fibers dissociated by collagenase and maintained in culture. Up to ten hours after dissociation, there were no changes in either the distribution or the biophysical properties of junctiona l acetylcholine receptors. In long-term culture (5 to 14 days), a new type of acetylcholine receptor was inserted all over the muscle fibers ; the channel properties were characterized by a longer open time and a smaller conductance, similar to what has been observed in in vivo de nervated muscles. Using autoradiography, we found that during culture an impaired incorporation of new acetylcholine receptors in the former endplates caused a progressive decrease in the density of junctional acetylcholine receptors. This contrasts with muscle fibers denervated in vivo, where the density of receptors does not change after denervat ion.