MUSCARINIC EXCITATION: A MICROELECTROPHORETIC STUDY ON CULTURED SMOOTH MUSCLE CELLS

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Abstract
1 Acetylcholine was applied iontophoretically to smooth muscle cells cultured from taeniae coli of new-born guinea-pigs. Responses were recorded with intracellular microelectrodes. 2 Acetylcholine induced depolarization, spike generation and contraction. Large conductance increases could be measured during the action of acetylcholine. 3 Injection of depolarizing currents through the recording electrode reversed the sign of potential responses. The reversal potential was −5 to −25 mV. 4 Minimum latencies of responses to acetylcholine were 120–500 ms. These values were not attributable to diffusion time. 5 Attention is drawn to the long latencies of a variety of muscarinic responses, and the suggestion made that muscarinic mechanisms as a class may be characterized by a long activation time.