Two dissociable phases in the contractile response of the guinea pig isolated vas deferens to adenosine triphosphate.
The effects of the ATP affinity label periodate-oxidized ATP (ATP-2',3'-dialdehyde; P-ATP) on contractile responses of the guinea pig vas deferens to ATP was characterized and compared to the effects of the specific P2x-purinoceptor photoaffinity label antagonist, arylazido aminopropionyl ATP (ANAPP3). After incubation of vas deferens with 10(-2) M P-ATP for 5 min, the second phase of biphasic contractions to ATP was inhibited selectively. The inhibitory effect of P-ATP was specific for ATP, and resulted from affinity labeling in that it was long-lasting, was not reversed by washing, was related in magnitude to exposure period and was attenuated by ATP present during the incubation. In contrast to P-ATP, ANAPP3 inhibited selectively the first phase of ATP-induced responses. P-ATP and ANAPP3 together inhibited both phases of response. P-ATP inhibited selectively the second phase of responses to 5'-substituted ATP analogs which develop a prolonged second phase [e.g., adenosine 5'-O-(3-thiotriphosphate) and adenosine tetraphosphate] or an abbreviated second phase (e.g., beta,gamma-methylene ATP, beta,gamma-imido ATP and alpha,beta-methylene ATP). The greater the duration of the second phase, the more pronounced was the inhibitory effect. Two distinct and dissociable mechanisms mediate the biphasic response to ATP: the initial phase involves ANAPP3-sensitive P2x-purinoceptors, whereas the second is blocked by P-ATP and appears to involve cleavage of the phosphate chain. An additional effect observed as a result of P-ATP-treatment was potentiation of the first phase of contraction to ATP. This novel and irreversible effect may arise from the inhibition of degradative ecto-phosphohydrolase activity.
Fedan
J S
JS
Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Morgantown, West Virginia.
Lamport
S J
SJ
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D000345:Affinity Labels; D000818:Animals; D001386:Azides / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D014649:Vas Deferens / Q000187:drug effects
C012761:3'-O-(3-(N-(4-azido-2-nitrophenyl)amino)propionyl)adenosine-5'-triphosphate; D000345:Affinity Labels; D001386:Azides; C004282:periodate-oxidized adenosine 5'-triphosphate; D000255:Adenosine Triphosphate