ACETYLCHOLINE RECEPTOR CHANNEL PROPERTIES IN NON-INNERVATED EMBRYONIC MUSCLE CELLS IN CULTURE

ALLAN STEVEN GREENBERG, Purdue University

Abstract

Muscle cell cultures were prepared from Xenopus embryos (stages 18-19) prior to formation of synaptic contacts. The "giga seal" patch clamp method was used to record AchR single channel currents from cells maintained for 4-6 days in culture. Two classes of single channel events were characterized and could be distinguished on the basis of average conductance and channel open time. The differences in channel conductance and open time between the two classes of events appear analogous to the differences betwen junctional and extrajunctional AchRs of adult muscle. A comparison was made between single channel events activated by either, acetylcholine or suberyldicholine and showed only minimal differences in channel properties, within each class of events. In order to characterize single channel properties of (presumed) recently inserted receptors, existing AchRs were blocked with (alpha)-bungarotoxin ((alpha)-BGT) and recordings were made over the next 3-8 hours. Both types of single channel events were observed and their properties were not significantly different from those of more "mature" receptors. Some of the cells pretreated with (alpha)-BGT exhibited clustering of events followed by long quiescent periods. This is in contrast to the relatively maintained frequency of single channel events found in control records. This atypical pattern of event occurences seen for some recently inserted receptors was not simply a function of the toxin of the reduced numbers of functional receptors. Furthermore, the single channel behavior of recently inserted receptors qualitatively resembled that displayed by receptors in a desensitized state (Sakmann et al., 1980). This may suggest that newly inserted receptors are more prone to desensitization than receptors with a longer history on the sacolemma.

Degree

Ph.D.

Subject Area

Anatomy & physiology|Animals

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