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Characterization off purine receptors in the rat gastric fundus
1210 P.we.042 1
Characterization of purine receptors in the rat gastric fundus Lefebvre, R.A. and Burnstock *, G. Heymans Institute of Pharmacology, University of Gent Medical School, De Pintelaan 185, B-9000 Gent, Belgium and * Department of Anatomy and Developmental Biology, University College London, Gower Street, London WCIE 6BT, U.K
Purinoceptors have been subclassified into P~- and P2-purinoceptors, with preferential potency for adenosine and ATP respectively (Burnstock, 1978). P2-purinoceptors have been further subdivided into P2x- and P2y-purinoceptors, based on the rank order of potency oi" purine agonists and on selective antagonism (Burnstock and Kennedy, 1985). The effect of ATP in the longitudinal muscle strip of the rat gastric fundus is biphasic, relaxation followed by contraction (Lefebvre, 1986), and the present study was set up to characterize the purinoceptors involved. Longitudinal muscle strips of the gastric fundus of male Wistar rats were isolated and set up for auxotonic tension measurement in Biilbring-modified Krebs' solution at 37 o C, bubbled with 95% 02 and 5% CO2. During preliminary experiments, it was shown that 10 -4 M ATP usually induced a small rela.~tion followed by a contraction at resting tension, induced a larger relaxation followed by a small rebound contraction when tone was raised with 10 -~ M carbachol and had little effect when tone was still further increased with 10 -6 M carbachol. The influence of the purines was therefore investigated at resting tension and when tone was raised by administration of 10- ~ M carbachol. At resting tension, ATP (3.10 -6 M-10-3 M) usually produced a small relaxation followed by concentration-dependent contractions. The effec.t of 2-methylthioATP (10-~-10 -s M) was s;milar to that of ATP, while a,~-methyleneATP only induced contractions with 10-s M or more and adenosine (10-5-3.10-3 M) had no effect. At raised tone, both ATP and 2-methylthioATP induced concentration-dependent relaxations, followed by rebound contraction above the carbachol-induced tone level, a,/~-MethyleneATP and adenosine only induced concentration-dependent relaxations and their maximal relaxant effect was much more pronounced than that of ATP. The rank order of potency of the purines producing relaxation was 2-methylthioATF > a,~-methyleneATP > ATP > adenosine. During incubation with indomethacin (5.10 -5 M), the contraction induced by ATP (10 -4 M) in both low and high tone conditions was significantly antagonized. The relaxant effect, of ATP (10 -4 M) at raised tone was reduced by 57% in the presence of reactive blue 2 (10 -4 M) and by 85% after desensitizing the tissue to a,/3-methyleneATP by repetitive administration of 3.10 -s M. It is concluded that the contractile effect of ATP in the rat gastric fundus is due to stimulation of prostaglandin biosynthesis. Although some of the findings (2-methylthioATP being the most potent, sensitivity to reactive blue 2) seem to point out that the purinoceptor subtype mediating relaxation in the rat gastric fundus belongs to the P2y-type, other observations suggest that it may differ from the P2,, and P2y-receptors, which are clearly distinguishable in a number of other tissues. R.A. Lefebvre is a Senior Research Associate of the National Fund for Scientific Research.
References Burnstock, G., 19"/8, Cell Membrane Receptors for Drugs and Hormones: A Multidisciprinary Approach, eds. R.W. Straub and L. Boris, pp. 107-118, Raven Press. Burnstock, G. and Kennedy, C. (1985), Gen. Pharmacol. 16, 433. Lefebvre, R.A., 1986, Arch. int. Pharmacodyn. 280, Suppl., 110.
Characterization of purine receptors in the rat gastric fundus Lefebvre, R.A. and Burnstock *, G. Heymans Institute of Pharmacology, University of Gent Medical School, De Pintelaan 185, B-9000 Gent, Belgium and * Department of Anatomy and Developmental Biology, University College London, Gower Street, London WCIE 6BT, U.K
Purinoceptors have been subclassified into P~- and P2-purinoceptors, with preferential potency for adenosine and ATP respectively (Burnstock, 1978). P2-purinoceptors have been further subdivided into P2x- and P2y-purinoceptors, based on the rank order of potency oi" purine agonists and on selective antagonism (Burnstock and Kennedy, 1985). The effect of ATP in the longitudinal muscle strip of the rat gastric fundus is biphasic, relaxation followed by contraction (Lefebvre, 1986), and the present study was set up to characterize the purinoceptors involved. Longitudinal muscle strips of the gastric fundus of male Wistar rats were isolated and set up for auxotonic tension measurement in Biilbring-modified Krebs' solution at 37 o C, bubbled with 95% 02 and 5% CO2. During preliminary experiments, it was shown that 10 -4 M ATP usually induced a small rela.~tion followed by a contraction at resting tension, induced a larger relaxation followed by a small rebound contraction when tone was raised with 10 -~ M carbachol and had little effect when tone was still further increased with 10 -6 M carbachol. The influence of the purines was therefore investigated at resting tension and when tone was raised by administration of 10- ~ M carbachol. At resting tension, ATP (3.10 -6 M-10-3 M) usually produced a small relaxation followed by concentration-dependent contractions. The effec.t of 2-methylthioATP (10-~-10 -s M) was s;milar to that of ATP, while a,~-methyleneATP only induced contractions with 10-s M or more and adenosine (10-5-3.10-3 M) had no effect. At raised tone, both ATP and 2-methylthioATP induced concentration-dependent relaxations, followed by rebound contraction above the carbachol-induced tone level, a,/~-MethyleneATP and adenosine only induced concentration-dependent relaxations and their maximal relaxant effect was much more pronounced than that of ATP. The rank order of potency of the purines producing relaxation was 2-methylthioATF > a,~-methyleneATP > ATP > adenosine. During incubation with indomethacin (5.10 -5 M), the contraction induced by ATP (10 -4 M) in both low and high tone conditions was significantly antagonized. The relaxant effect, of ATP (10 -4 M) at raised tone was reduced by 57% in the presence of reactive blue 2 (10 -4 M) and by 85% after desensitizing the tissue to a,/3-methyleneATP by repetitive administration of 3.10 -s M. It is concluded that the contractile effect of ATP in the rat gastric fundus is due to stimulation of prostaglandin biosynthesis. Although some of the findings (2-methylthioATP being the most potent, sensitivity to reactive blue 2) seem to point out that the purinoceptor subtype mediating relaxation in the rat gastric fundus belongs to the P2y-type, other observations suggest that it may differ from the P2,, and P2y-receptors, which are clearly distinguishable in a number of other tissues. R.A. Lefebvre is a Senior Research Associate of the National Fund for Scientific Research.
References Burnstock, G., 19"/8, Cell Membrane Receptors for Drugs and Hormones: A Multidisciprinary Approach, eds. R.W. Straub and L. Boris, pp. 107-118, Raven Press. Burnstock, G. and Kennedy, C. (1985), Gen. Pharmacol. 16, 433. Lefebvre, R.A., 1986, Arch. int. Pharmacodyn. 280, Suppl., 110.