Electrophysiological characterization of histamine receptor subtypes in sheep cardiac Purkinje fibers.
The histamine-receptor-subtype-mediated effects on action potentials of electrically driven and spontaneously active isolated sheep cardiac Purkinje fibers were investigated using H1- and H2-selective agonists and antagonists. In electrically stimulated Purkinje fibers, histamine (3 mumol/l) increased the action potential plateau height, decreased the action potential duration measured at a repolarization level of -60 mV and enhanced the pacemaker activity. These effects were abolished by the H2-selective antagonist cimetidine (30 mumol/l), but were not impaired by the H1-selective antagonist dimetindene (0.3 mumol/l). In spontaneously active Purkinje fibers, histamine (10 mumol/l) increased the spontaneous rate by 24%, the slope of diastolic depolarization by 45% and shortened the duration of the diastole by 32% of the respective control measurements. These effects were blocked by 30 mumol/l cimetidine, but remained unchanged in the presence of 0.3 mumol/l dimetindene. Concentration-response curves of histamine were shifted to the right by approximately 2 logarithmic units in the presence of 30 mumol/l cimetidine, but were not influenced in the presence of 0.3 mumol/l dimetindene. The H2-selective agonist impromidine (0.001-0.3 mumol/l) had similar actions as histamine on spontaneously active Purkinje fibers, while the H1-selective agonist 2-(2-pyridyl-)ethylamine was ineffective. It is concluded that the pronounced stimulatory action of histamine on spontaneous activity in sheep cardiac Purkinje fibers is exclusively mediated by H2 receptors.
Institut für Pharmakologie, Heinrich-Heine Universität, Düsseldorf, FRG.
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U
Thome
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F
Berger
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U
Borchard
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D
Hafner
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002927:Cimetidine / Q000494:pharmacology; D004558:Electric Stimulation; D006632:Histamine / Q000494:pharmacology; D017442:Histamine Agonists / Q000494:pharmacology; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D011690:Purkinje Fibers / Q000187:drug effects / Q000502:physiology*; D011969:Receptors, Histamine H1 / Q000187:drug effects / Q000502:physiology*; D011970:Receptors, Histamine H2 / Q000187:drug effects / Q000502:physiology*; D012756:Sheep
D017442:Histamine Agonists; D006634:Histamine H1 Antagonists; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D002927:Cimetidine; D006632:Histamine