AhV_aPA-induced vasoconstriction involves the IP3Rs-mediated Ca(2+) releasing.

AhV_aPA, the acidic PLA2 purified from Agkistrodon halys pallas venom, was previously reported to possess a strong enzymatic activity and can remarkably induce a further contractile response on the 60 mM K(+)-induced contraction with an EC50 in 369 nM on mouse thoracic aorta rings. In the present study, we found that the p-bromo-phenacyl-bromide (pBPB), which can completely inhibit the enzymatic activity of AhV_aPA, did not significantly reduce the contractile response on vessel rings induced by AhV_aPA, indicating that the vasoconstrictor effects of AhV_aPA are independent of the enzymatic activity. The inhibitor experiments showed that the contractile response induced by AhV_aPA is mainly attributed to the Ca(2+) releasing from Ca(2+) store, especially sarcoplasmic reticulum (SR). Detailed studies showed that the Ca(2+) release from SR is related to the activation of inositol trisphosphate receptors (IP3Rs) rather than ryanodine receptors (RyRs). Furthermore, the vasoconstrictor effect could be strongly reduced by pre-incubation with heparin, indicating that the basic amino acid residues on the surface of AhV_aPA may be involved in the interaction between AhV_aPA and the molecular receptors. These findings offer new insights into the functions of snake PLA2 and provide a novel pathogenesis of A. halys pallas venom.