Calcium influx and release mechanism(s) in histamine-induced myometrial contraction in buffaloes

The present study was undertaken to characterize the presence of histamine H1R using molecular biology tools and unravel the influx and release mechanism(s) involved in calcium signalling cascades in histamine-induced myometrial contraction in buffaloes. The presence of H1R mRNA transcript and immunoreactive membrane protein in buffalo myometrium was confirmed by RT-PCR and Western blot analysis. Further, histamine produced concentration-dependent (1 nM–10 μM) contraction in buffalo myometrium with a potency of 7.13 ± 0.11. When myometrial strips were pre-incubated either with Ca2+ free solution or with nifedipine, a L-type Ca2+ channel blocker, dose response curve (DRC) of histamine was significantly (P < 0.05) shifted towards right with decline in maximal contraction (Emax). Reduction in Emax of histamine in the presence of nifedipine (55.75 ± 3.10%) was significantly (P < 0.001) greater than that in the presence of ruthenium red (93.61 ± 3.43%), a blocker of IP3-gated and RyR-sensitive Ca2+ channels. Moreover, histamine produced only 26.87 ± 1.99% of the maximum contraction in the presence of both nifedipine and CPA (blocker of sarco-endoplasmic reticulum Ca2+-ATPase). Interestingly, following concurrent exposure to U-73122 (a PL-C inhibitor) and nifedipine, the DRC of histamine was significantly (P < 0.05) shifted towards left with increase in maximal contraction (126.30 ± 3.36%). Our findings in buffalo uterus thus suggest that influx of extracellular calcium plays a major role in histamine-induced myometrial contraction, while release of intracellular calcium through calcium-release channels of sarcoplasmic reticulum has a minor role. A possible involvement of non-selective cation channels in histamine-induced myometrial contraction cannot be ruled out, and therefore requires further investigations.