title: Comparison of the effects of apamin, a Ca2+-dependent K+ channel blocker, and arylazido aminopropionyl ATP (ANAPP3), a P2-purinergic receptor antagonist, in the guinea-pig vas deferens.
abstract: Apamin, which blocks Ca2+-dependent increases in K+ permeability, antagonizes ATP-induced relaxation of several smooth muscles. The ATP photoaffinity label arylazido aminopropionyl ATP (ANAPP3), following its photolysis in the presence of the guinea-pig vas deferens, antagonizes contractile responses to ATP. This study was conducted to determine whether apamin antagonizes ATP-induced responses in the guinea-pig vas deferens, and also to evaluate whether ANAPP3 antagonizes responses to ATP by interfering with Ca2+-dependent K+ permeability changes. Apamin (10(-6) M) potentiated ATP-induced contractions. This potentiation was nonspecific in that responses to norepinephrine, histamine and acetylcholine also were enhanced; responses to KCl were unaffected. To evaluate the possible interactions between the two agents at the same cellular site, the effect of apamin was examined in ANAPP3-treated tissues. In such tissues apamin did not potentiate the residual responses to ATP; however, apamin was nevertheless able to potentiate responses of ANAPP3-treated tissues to norepinephrine, histamine and acetylcholine, and responses to KCl remained unaffected. These studies provide additional support for the view that ANAPP3 antagonizes ATP-induced responses of the guinea-pig vas deferens by blocking P2-purinergic receptors. The antagonism by ANAPP3 is not attributable to a blockade of Ca2+-dependent K+ permeability changes.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology*; D001386:Azides / Q000494:pharmacology*; D001514:Bee Venoms / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*; D017981:Receptors, Neurotransmitter / Q000187:drug effects*; D011983:Receptors, Purinergic; D014649:Vas Deferens / Q000187:drug effects
chemical_list: C012761:3'-O-(3-(N-(4-azido-2-nitrophenyl)amino)propionyl)adenosine-5'-triphosphate; D001386:Azides; D001514:Bee Venoms; D007473:Ion Channels; D017981:Receptors, Neurotransmitter; D011983:Receptors, Purinergic; D001030:Apamin; D000255:Adenosine Triphosphate; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium