Interaction of histamine with adrenergic smooth-muscle neurotransmission. II. Significance of calcium ions for the effects of histamine on contractions induced by endogenous noradrenaline.
The role of Ca2+ for the effects of histamine on contractions induced by electrostimulation has been studied on smooth-muscle organs with adrenergic neurotransmission (rat anococcygeal muscle and vas deferens). The low Ca2+-concentrations in the organ bath (below 1.8 mM) reduce the amplitude of the smooth-muscle contractions in response to electrostimulation (more markedly at the low frequency), at the same time potentiating the inhibitory action of histamine on the electrostimulation-induced contractions of the isolated preparations. Raising the Ca2+-concentration in the nutrient medium increases the magnitude of the contractions in response to electrostimulation. At the same time the high Ca2+-concentrations weaken the second (inhibitory) phase of the action of histamine on the electrostimulation-induced contractions of the smooth-muscle preparations. The potentiating action of histamine on contractions in response to electrostimulation is not essentially influenced by the changes in Ca2+-concentration. The data obtained show that Ca-ions may play a role in the mechanism of the inhibitory action of histamine on the smooth-muscle adrenergic neurotransmission, which is assumed to be mediated by presynaptic H2-histaminergic receptors.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation; D006632:Histamine / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009638:Norepinephrine / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*
D011941:Receptors, Adrenergic; D006632:Histamine; D002118:Calcium; D009638:Norepinephrine