Fig. 7. 4-AP blocks the enterin-induced hyperpolarization. (A) Effect of 10^-5 moll^-1 4-AP on the 10^-6 moll^-1 ENpa-induced hyperpolarization of the muscle. (B) The concentration—response relationship of the 4-AP block. Amplitude of the ENpa-induced hyperpolarization in the presence of 4-AP was normalized to that seen in the absence of 4-AP. Values are means ± S.E.M. (N=3-5) of the ENpa-induced hyperpolarization plotted against [4-AP].