Effects of histamine on the guinea-pig stomach: excitation of smooth muscle and inhibition of transmitter release.

1 The effects of histamine on electrical responses of smooth muscle cells of the guinea-pig stomach were studied. 2 In the fundus, histamine (above 10(-6) M) depolarized the membrane and decreased the membrane resistance. In the antrum, the slow waves were enhanced by histamine, without change in the resting membrane potential or membrane resistance (10(-7)-10(-6) M), or with depolarization of the membrane (above 10(-5) M). 3 When the effects of histamine on neuromuscular transmission were estimated from changes in the amplitude of junction potentials, the amine (above 10(-7) M) inhibited the excitatory junction potential (e.j.p.) recorded in the fundus. Inhibitory junction potentials (i.j.p.) recorded in the antrum and atropine-treated fundus were also inhibited by histamine. 4 Repolarization of the histamine-induced depolarization to the resting potential level did not restore the amplitude of the e.j.p. to the control value. 5 These actions of histamine on the smooth muscle cells and on junction potentials were inhibited by either mepyramine or cimetidine, agents which block the H1- and H2-receptor, respectively. 6 It is concluded that in the guinea-pig stomach, histamine exerts a direct excitatory effect on the smooth muscle cells and has inhibitory actions on cholinergic excitatory and non-adrenergic, non-cholinergic inhibitory transmission.