Membrane mechanism associated with muscarinic receptor activation in single cells freshly dispersed from the rat anococcygeus muscle

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Abstract
The mechanism of action of carbachol was studied on freshly dispersed cells of the rat anococcygeus using microelectrodes and patch pipettes. Micro‐ionophoretic application of carbachol evoked reproducible depolarizations which were reduced or blocked by atropine (10−7‐10−6 m). The time courses of the responses to noradrenaline and carbachol were similar. The reversal potential of the carbachol‐induced response was −3.8 mV and similar to the value (‐6.2 mV) found for noradrenaline. During the response to carbachol the membrane conductance was increased. At depolarized membrane potentials carbachol evoked biphasic membrane responses suggesting an increase in two separate ionic conductances. With patch pipettes in the whole‐cell configuration under voltage‐clamp, carbachol produced an inward current at a holding potential of −50 mV. The inward current was associated with an increase in membrane conductance with an equilibrium potential of about 0 mV. It is suggested that muscarinic receptors and adrenoceptors in the rat anococcygeus may activate similar membrane conductances. The most prominent mechanism is an increase in chloride ion conductance.