The effect of histamine on the smooth muscle cells of the ear artery of the rabbit.

Histamine activates both H1- and H2-receptors in the ear artery of the rabbit. The specific action of these receptor activations on the membrane potential and the force development has been investigated by using the H1-blocking agent mepyramine and the H2-blocking agent cimetidine. H1-activation depolarizes and increases force development, while H2-activation hyperpolarizes and reduces force development. These effects on the force development can occur independently of the changes of the membrane potential. By determining the effect of histamine on tissues which were denervated with 6-hydroxydopamine it was shown that histamine exerts its effect directly on the smooth muscle cells. Na-deficiency depolarizes the smooth muscle cells, but it also reduces the changes of the membrane potential and the force development induced by H1-stimulation. K-free medium prevents the hyperpolarizing effect of H2-activation. As far as the ion fluxes are concerned an H1-activation is found to induce an increased efflux of K while a simultaneous H2-activation only reduces the increase of flux induced by H1-activation. H1-activation induces a release of Ca from the intracellular Ca stores, while H2-activation inhibits this release.