Calcium Channels, Rho-Kinase, Protein Kinase-C, and Phospholipase-C Pathways Mediate Mercury Chloride-Induced Myometrial Contractions in Rats

Abstract

Adverse effects of mercury on female reproduction are reported; however, its effect on myogenic activity of uterus and mechanism thereof is obscure. Present study was undertaken to unravel the mechanistic pathways of mercuric chloride (HgCl₂)-induced myometrial contraction in rats. Isometric tension in myometrial strips of rats following in vitro exposure to HgCl₂ was recorded using data acquisition system-based physiograph. HgCl₂ produced concentration-dependent (10 nM–100 μM) uterotonic effect which was significantly (p < 0.05) reduced in Ca²⁺-free solution and inhibited in the presence of nifedipine (1 μM), a L-type Ca²⁺ channel blocker, thus suggesting the importance of extracellular Ca²⁺ and its entry through L-type calcium channels in HgCl₂-induced myometrial contractions in rats. Cumulative concentration-response curve of HgCl₂ was significantly (p < 0.05) shifted towards right in the presence of Y-27632 (10 μM), a Rho-kinase inhibitor, suggesting the involvement of Ca²⁺-sensitization pathway in mediating HgCl₂-induced myometrial contraction. HgCl₂-induced myometrial contraction was also significantly (p < 0.05) inhibited in the presence of methoctramine or para-fluoro-hexahydro-siladifenidol, a selective M₂ and M₃ receptor antagonists, respectively, which evidently suggest that mercury also interacts with M₂ and M₃ muscarinic receptors to produce myometrial contractions. U-73122 and GF-109203X, the respective inhibitors of PLC and PKC-dependent pathways, downstream to the receptor activation, also significantly (p < 0.05) attenuated the uterotonic effect of HgCl₂ on rat uterus. Taken together, present study evidently reveals that HgCl₂ interacts with muscarinic receptors and activates calcium signaling cascades involving calcium channels, Rho-kinase, protein kinase-C, and phospholipase-C pathways to exert uterotonic effect in rats.

Graphical Abstract

Graphical abstract depicting the mechanism of mercury-induced myometrial contraction in rats. M receptor: Muscarinic receptor; PIP2: phospho-inositol bisphosphate; PLC: phospholipase-C; DAG: diacyl glycerol; IP3: inositol triphosphate; IP3R: inositol triphosphate receptor; PKC; protein kinase-C; MLCP: myosin light chain phosphatise; MYPT: myosin phosphatase; SR: sarco-endoplasmic reticulum

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