Carbachol and pirenzepine discriminate effects mediated by two muscarinic receptor subtypes on hippocampal neurons in vitro.

Measurement of [Cch] in the bath and in slices demonstrated a considerable concentration discrepancy between the bath and the extracellular space. With fast (bolus) application of Cch this discrepancy is due to the speed of diffusion, while equilibration with continuous application is considerably impaired by cellular uptake of Cch (Creese and Taylor, 1967). Low concentrations (less than or equal to 1 microM) of Cch reduce the afterhyperpolarization following a train of action potentials and depolarize the membrane. Analysis of [Cch]0 (t) and the effects of pirenzepine allowed these effects to be assigned to two different muscarinic receptor subtypes.