NNOS mediates relaxation in corpus cavernosum mice strips improved by Tx2‐6 toxin from Phoneutria nigriventer spider via cGMP increase

Abstract

A toxin from the venom of Phoneutria nigriventer spider, Tx2‐6, causes priapism in mice and relaxation of rat cavernosal tissue. The aim of this study is to investigate the involvement of NOS isoforms and cGMP in the action of the toxin Tx2‐6 on erectile tissue. We isolated cavernosum strips from eNOS and nNOS knock out (KO) mice. The strips were incubated with bretylium tonsilate (3x10−5M) to block adrenergic neurotransmission. Following contraction induced by phenylephrine (10−5 M), the strips were made to relax in response to electrical field stimulation (EFS). Cumulative concentration‐response curves to acetylcholine (10−9 to 10−5M) were performed in absence and presence of Tx2‐6. cGMP levels were analyzed using kit (Cayman) in presence of Tx2‐6 and this toxin plus L‐NAME (10−4M). The action of the N‐type calcium channels antagonist, ω‐conotoxin GVIA (10−6M) on EFS was evaluated. Results showed relaxation increased in the presence Tx2‐6 toxin (10nM) in wild type and eNOS KO mice but not in nNOS KO mice. Acetylcholine seems not be involve in the relaxation improved by Tx2‐6. cGMP levels significantly increased in the presence of Tx2‐6. This increase was abolished by L‐NAME and ω‐conotoxin GVIA. This study indicates that Tx2‐6 improves the erectile response, probably via activation of calcium channels by slowing the inactivation of Na+ channels in nitrergic nerves facilitating NO production from nNOS and consequently increased cyclic GMP.