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.
The pharmacological effects of apamin (24345162) and arylazido- aminopropionyl-adenosine-triphosphate (ANAPP3) on the guinea-pig vas deferens were studied in-vitro. Vasa deferentia obtained from guinea-pigs were placed in an organ chamber containing modified Krebs Henseleit solution and 0 to 0.01 molar (M) adenosine- triphosphate (ATP), 0 to 1000 nanomolar (nM) apamin, or 0 to O.2M potassium-chloride, acetylcholine, histamine, or norepinephrine. The effects on induced isometric contractile responses were evaluated. In similar experiments, guinea-pig vasa deferentia were treated with apamin, ANAPP3, ATP, potassium-chloride, acetylcholine, histamine, or norepinephrine. The effects on the contractile response of the vas deferens were investigated. Apamin at 0.000001M potentiated contractions induced by ATP, norepinephrine, histamine, and acetylcholine. Apamin had no effect on contractions induced by potassium-chloride. Apamin potentiated the responses of ANAPP3 treated vasa deferentia to norepinephrine, histamine, and acetylcholine. The responses to ATP and potassium-chloride were not affected. The authors conclude that apamin is not an ATP antagonist in the guinea-pig vas deferens and that the antagonism of ATP induced responses by ANAPP3 is P2-purinergic receptor mediated and does not involve an interaction with calcium ion dependent potassium ion channels.