Evidence that the P2x purinoceptor of the smooth muscle of the guinea pig vas deferens is an ATP4- receptor.
Fedan-JS; Dagirmanjian-JP; Attfield-MD; Chideckel-EW
J Pharmacol Exp Ther 1990 Oct; 255(1):46-51
In solutions containing Mg2+ and Ca2+, ATP is in equilibrium between the tetrabasic form (ATP4-) and its bidentate coordination complexes, i.e., MgATP2- and CaATP2-. We sought evidence to determine whether contractions of the smooth muscle of the guinea pig vas deferens to ATP are in response to ATP4- or its bidentate complexes. Contractions to ATP were elicited in seven modified Krebs-Henseleit solutions containing varied concentrations of free and total Mg2+ and Ca2+ to alter the concentration of ATP4- at given ATPtotal concentrations. As the concentration of Mg2+ increased the concentration of ATP required to stimulate contraction to an equivalent degree also increased. Regardless of the free or total Mg2+ and Ca2+ concentrations, response magnitude was generally correlated with [ATP4-]. This suggests that ATP4- is the agonist at the P2x purinoceptor of the guinea pig vas deferens. The potency of ATP4- is high; the threshold, occurring at approximately 1 nM ATP4-, is 1000-fold less than that for norepinephrine. The implications of ATP4- as agonist are discussed in relation to adenine nucleotide potency, metabolism and P2 purinoceptor classification.
Physiological-factors; Physiological-effects; In-vitro-study; Muscle-function; Muscle-contraction; Musculoskeletal-system; Muscles; Muscle-physiology; Dose-response
Journal of Pharmacology and Experimental Therapeutics