Calcium signaling cascades differentially regulate PGF 2α -induced myometrial contractions in water buffaloes (Bubalus bubalis).

This study unravels the differential involvement of calcium signaling pathway(s) in PGF2α -induced contractions in myometrium of nonpregnant (NP) and pregnant buffaloes. Compared to the myometrium of pregnant animals, myometrium of NP buffaloes was more sensitive to PGF2α as manifested by changes in mean integral tension (MIT) and tonicity. In the presence of nifedipine, myometrial contraction to PGF2α was significantly attenuated in both NP and pregnant uteri; however, mibefradil and NNC 55-0396 produced inhibitory effects only in uterus of pregnant animals, thus suggesting the role of extracellular Ca2+ influx through nifedipine-sensitive L-type Ca2+ -channels both in NP and pregnant, but T-type Ca2+ channels seem to play a role only during pregnancy. Entry of extracellular Ca2+ is triggered by enhanced functional involvement of Pyr3-sensitive TRPC3 channels and Rho-kinase pathways as evidenced by a significant rightward shift of the concentration-response curve of PGF2α in the presence of Pyr3 and Y-27632 in NP myometrium. But significant down-expressions of TRPC3 and Rho-A proteins during pregnancy apparently facilitate uterine quiescence. In the presence of Ca2+ -free solution and cyclopiazonic acid (SERCA blocker), feeble contraction to PGF2α was observed in both NP and pregnant myometrium which suggests minor role of intracellular source of Ca2+ in mediating PGF2α -induced contractions in these tissues.