RESUMO
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 Kâº-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 Ca²âº releasing from Ca²âº store, especially sarcoplasmic reticulum (SR). Detailed studies showed that the Ca²âº 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.
Assuntos
Cálcio/metabolismo , Contração Muscular/efeitos dos fármacos , Fosfolipases A2/farmacologia , Venenos de Serpentes/enzimologia , Vasoconstrição/efeitos dos fármacos , Acetofenonas/farmacologia , Agkistrodon , Animais , Aorta Torácica/efeitos dos fármacos , Aorta Torácica/metabolismo , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Camundongos , Camundongos Endogâmicos ICR , Miócitos de Músculo Liso/efeitos dos fármacos , Miócitos de Músculo Liso/metabolismo , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismo , Retículo Sarcoplasmático/efeitos dos fármacos , Retículo Sarcoplasmático/metabolismo , Vasoconstritores/farmacologiaRESUMO
Phospholipases A2 (PLA2s) are the major component of snake venoms and exert a variety of relevant toxic actions such as neurotoxicity and myotoxicity, amongst others. An acidic PLA2, here named AhV_aPA, was purified from Agkistrodon halys pallas venom by means of a three-step chromatographic procedure. AhV_aPA migrated as a single band on SDS-PAGE gels, with a molecular weight of about 14â kDa. Like other acidic aPLA2s, AhV_aPA has high enzymatic activity. Tension measurements of mouse thoracic aortic rings remarkably indicated that AhV_aPA could induce a further contractile response on the 60â mM K+-induced contraction, with an EC50 of 369â nmolâ l(-1). Rod-shaped crystals were obtained by the hanging-drop vapour-diffusion method and diffracted to a resolution limit of 2.30â Å. The crystals belonged to space group P222, with unit-cell parameters a=44.27, b=68.39, c=81.54â Å.