Muscarinic excitation: a microelectrophoretic study on cultured smooth muscle cells.

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.