Excision of membrane patches reduces the mean open time of nicotinic acetylcholine receptors

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Abstract
Excision of membrane patches from clonal BC3H1 cells to the inside-out configuration reduces the mean open time and burst duration of skeletal muscle nicotinic acetylcholine receptors. The channel conductance is not altered. Our results indicate that the rates for several steps in receptor activation are affected. The altered receptors apparently form a homogeneous population. Patterns of activity similar to that seen after excision are seen infrequently in recordings from cell-attached patches, suggesting that receptors with this type of altered function are present in intact membranes. The extent and rate of the reduction in mean open time after excision are similar at acetylcholine concentration over a 1000-fold range, indicating that the alteration does not depend on the state of ligation of the receptor. The extent and rate also are similar at room temperature and at 11° C. The changes seen indicate that careful comparisons to intact preparations are necessary when studying the gating of channels in excised patches or following reconstitution into artificial membranes.