Nitric oxide-induced vasorelaxation in response to PnTx2-6 toxin from Phoneutria nigriventer spider in rat cavernosal tissue.
BACKGROUND
Priapism is one of several symptoms observed in accidental bites by the spider Phoneutria nigriventer. The venom of this spider is comprised of many toxins, and the majority has been shown to affect excitable ion channels, mainly sodium (Na(+) ) channels. It has been demonstrated that PnTx2-6, a peptide extracted from the venom of P. nigriventer, causes erection in anesthetized rats and mice.


OBJECTIVE
We investigated the mechanism by which PnTx2-6 evokes relaxation in rat corpus cavernosum.


METHODS
PnTx2-6 toxin potentiates nitric oxide (NO)-dependent cavernosal relaxation.


METHODS
Rat cavernosal strips were incubated with bretylium (3 × 10(-5) M) and contracted with phenylephrine (PE; 10(-5) M). Relaxation responses were evoked by electrical field stimulation (EFS) or sodium nitroprusside (SNP) before and after 4 minutes of incubation with PnTx2-6 (10(-8) M). The effect of PnTx2-6 on relaxation induced by EFS was also tested in the presence of atropine (10(-6) M), a muscarinic receptor antagonist, N-type Ca(2+) channel blockers (ω-conotoxin GVIA, 10(-6) M) and sildenafil (3 × 10(-8) M). Technetium99m radiolabeled PnTx2-6 subcutaneous injection was administrated in the penis.


RESULTS
Whereas relaxation induced by SNP was not affected by PnTx2-6, EFS-induced relaxation was significantly potentiated by this toxin as well as PnTx2-6 plus SNP. This potentiating effect was further increased by sildenafil, not altered by atropine, however was completely blocked by the N-type Ca(2+) channels. High concentrated levels of radiolabeled PnTx2-6 was specifically found in the cavernosum tissue, suggesting PnTx2-6 is an important toxin responsible for P. nigriventer spider accident-induced priapism.


CONCLUSIONS
We show that PnTx2-6 slows Na(+) channels inactivation in nitrergic neurons, allowing Ca(2+) influx to facilitate NO/cGMP signalling, which promotes increased NO production. In addition, this relaxation effect is independent of phosphodiesterase enzyme type 5 inhibition. Our data displays PnTx2-6 as possible pharmacological tool to study alternative treatments for erectile dysfunction.
Nunes
Kenia P
KP
Biological Science Institute, Belo Horizonte, MG, Brazil. keniapedrosa@gmail.com
Cordeiro
Marta N
MN
Richardson
Michael
M
Borges
Marcia N
MN
Diniz
Simone O F
SO
Cardoso
Valbert N
VN
Tostes
Rita
R
De Lima
Maria Elena
ME
Webb
Robert Clinton
RC
Leite
Romulo
R
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000187:drug effects; D004558:Electric Stimulation; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009479:Neuropeptides / Q000494:pharmacology*; D009498:Neurotoxins / Q000494:pharmacology*; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D010413:Penis / Q000098:blood supply / Q000187:drug effects* / Q000294:innervation; D058986:Phosphodiesterase 5 Inhibitors / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D000068677:Sildenafil Citrate; D013111:Spider Venoms / Q000494:pharmacology*; D013450:Sulfones / Q000494:pharmacology; D013667:Technetium; D014664:Vasodilation / Q000187:drug effects*; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D018727:Muscarinic Antagonists; D009479:Neuropeptides; D009498:Neurotoxins; D020030:Nitric Oxide Donors; D058986:Phosphodiesterase 5 Inhibitors; D010879:Piperazines; D011687:Purines; D013111:Spider Venoms; D013450:Sulfones; C064022:Tx1 neurotoxin; D009599:Nitroprusside; D009569:Nitric Oxide; D013667:Technetium; D001285:Atropine; D020866:omega-Conotoxin GVIA; D000068677:Sildenafil Citrate