Ken-ichi Otsuguro, Toshio Ohta, Shigeo Ito and Yoshikazu Nakazato (*)
Laboratory of Pharmacology, Graduate School of Veterinary Medicine, Hokkaido
University, Sapporo 060-0818, Japan
(*) To whom correspondence should be addressed.
Abstract: Effects of purinoceptor antagonists on the relaxant
responses to adenine nucleotides were examined to characterize the subtypes
of P2-receptor in rat gastric circular muscle. In tissues contracted
by acetylcholine, a P2-receptor antagonist, suramin (100 microM),
inhibited the relaxant responses to ATP, adenosine 5'-O-(2-thiodiphosphate)
(ADPbetaS) and alpha,beta-methylene ATP but not that to adenosine, while
a P1-receptor antagonist, 8-phenyltheophylline (3 microM) did
vice versa. The inhibitory effect of suramin was more potent for the relaxant
responses to alpha,beta-methylene ATP than those to ATP or ADPbetaS. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic
acid (PPADS) (3 - 30 microM) and 4,4'-diisothiocyanatostilbene-2,2'-disulphonate
(DIDS) (30 and 1OO microM) inhibited the relaxation caused by alpha,beta-methylene
ATP but not by ATP, ADPbetaS or adenosine. These results suggest that ATP
and ADPbetaS cause relaxation via the classical P2Y receptors
resistant to PPADS and DIDS. In addition, alpha,beta-methylene ATP causes
relaxation via the distinct P2 receptors sensitive to PPADS and
DIDS in rat gastric circular muscle.
Keywords: ATP, Purinoceptor, Suramin, PPADS, DIDS