Figure 9. Muscarine acts at the M₃ receptor to inhibit GABA_A IPSCs.

A, superimposed traces show that 4-DAMP reverses muscarine-induced inhibition of a GABA_A IPSC in a concentration-dependent manner. B, superimposed traces show that pirenzepine also reduces the muscarine-induced inhibition of a GABA_A IPSC, but that the concentrations are much higher than those required for 4-DAMP. C, concentration-inhibition curves show reversal of muscarine (30 μM)-induced depression of IPSC amplitude by muscarine antagonists. The greater potency of 4-DAMP compared with pirenzepine suggests that M₃ receptors mediate the inhibitory effect of muscarine on GABA_A IPSCs. Results are means ±s.e.m. of 6 cells for 4-DAMP and 4 cells for pirenzepine.