Histamine-stimulated increases in intracellular calcium in the smooth muscle cell line, DDT 1MF-2

Abstract

Suspensions of undifferentiated cultured vas deferens smooth muscle cells (DDT 1MF-2) were loaded with the calcium-sensitive fluorescent dye fura-2. Exposure to histamine elicited a rapid and maintained increase in intracellular free calcium ([Ca 2+],) with an ec 50 of 1.3 ± 0.7 × 10 −5 M. The initial rise is a consequence of calcium release from intracellular stores, whereas the maintained or plateau phase, which is dependent upon the presence of extracellular calcium, is associated with calcium influx. Experiments in nominally Ca 2+-free buffer attenuated the initial rise in [Ca 2+] i (i.e. peak height) and virtually abolished the plateau phase. Re-addition of 2mM Ca 2+ (during experiments performed in nominally Ca 2+-free buffer) resulted in a return of the plateau phase. Pretreatment with the H 1-antagonist mepyramine (100 nM; K d = 1.0 ± 0.4 nM, N=3) completely blocks the response to histamine, whereas tiotidine (2 μM; H 2-antagonist) had no effect. In conclusion, the present data would suggest that functional H 1-receptors found in hamster vas deferens smooth muscle cells are typical of the “classical” H 1-receptor in both its control of intracellular Ca 2+ and sensitivity to antagonism by mepyramine.