Fig. 1.

Histamine-induced increases in excitability of intrinsic cardiac neurons increase postmyocardial infarction. Indexes of neuronal excitability were determined by monitoring voltage responses to positive current injections (indicated rectangular pulse, 0.3 nA, 500 ms). Action potential (AP) frequency was examined in neurons from control (untreated; A) preparations and tissue derived from chronic myocardial infarction (CMI; B) animals. Before application of exogenous neuromodulators (top), both cells showed a single AP with prolonged depolarization (phasic neuron). After a 1-s application of histamine (bottom), both neurons showed an increase in AP frequency, with the CMI cell showing a greater increase in firing frequency. Resting membrane potentials: untreated, −48 mV; CMI, −45 mV.