Histamine Increases Vascular Tone and Intracellular Calcium Level Using Both Intracellular and Extracellular Calcium in PorcinellCoronary Arteries

Abstract

AbstractEffects of histamine on the tone and intracellular calcium level (Ca2+1) in porcine coronary arteries were simultaneously investigated by use of the fura-2 microscopic fluorometrlc method. Histamine (10−e–10−4 M) induced concentration-dependent increases in tone and Ca2+1, but these responses were not sustained. Histamine induced a larger contraction than did KCl with a similar increase in Ca2+1. Depletion of the caffeine-sensitive Ca2+ store with ryanodine (3×10−5 M) and repetitive applications of caffeine (2.5×10−2 M) scarcely affected contractile and Ca2+1 responses to histamine. In Ca2+-free medium or in the presence of verapamil (10−e M), histamine produced a briefer increase in Ca2+1 and a smaller contraction than in normal medium. When histamine or caffeine was repetitively applied in Ca2+-tree medium, the first application produced an increase in Ca2+1 but the second application produced no increase. Although caffeine increased Ca2+1, after repetitive histamine applications, histamine failed to increase Ca2+1 after repetitive caffeine applications in Ca2+-free medium. These results indicate that vascular contraction induced by histamine may involve the following mechanisms: an increase in Ca2+ influx through Ca2+ channels, release of Ca2+ from the intracellular Ca2+ store which has an interaction with the caffeine-sensitive Ca2−1” store, and sensitization of contractile proteins to Ca2+.