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Mechanism of photoaffinity labeling of P2-purinergic receptors by arylazido aminopropionyl ATP in isolated guinea-pig vas deferens.
Fedan JS; Hogaboom GK; O'Donnell JP
Life Sci 1982 Nov; 31(18):1921-1928
The inhibitory effect of photolyzed arylazido aminopropionyl adenosine-triphosphate (AA ATP) on guinea-pig vas deferens in the presence of p-aminobenzoic-acid (150130) (PABA) was investigated. Vas deferens from albino-guinea-pigs were mounted in a continuously suffused organ bath. The tissues were photolyzed for 15 minutes in the presence of 0.0004 moles AA ATP at 37 degrees-C. Concentration response determinations were begun 10 minutes later. Control preparations were irradiated in the absence of AA ATP. Ten millimoles of PABA were added to the incubating tissue in the presence or absence of AA ATP. Contralateral control vas deferens received no treatment. Effects of PABA were also tested on magnesium adenosine-triphosphate (1476842) (Mg ATP), acetylcholine (51843), potassium-chloride (7447407), histamine (51456), and norepinephrine (51412) (NE). Photolysis of AA ATP for 15 minutes converted 80 percent of the compound to unknown products. The presence of PABA did not prevent the antagonism of ATP induced response by AA ATP. The absorption spectrum of AA ATP photolyzed in the presence of PABA was different from the one where PABA was absent. This difference suggested that additional reaction products were formed by covalent binding and arose from true photo affinity labeling of the receptor. The concentration curves of potassium- chloride, Mg ATP, and acetylcholine were not modified 10 to 23 minutes after incubation with PABA. PABA induced a significant, but reversible, antagonistic effect on histamine and NE induced contractions. Photolysis in the presence of PABA produced a slight potentiation of responses to ATP. The authors conclude that the mechanisms of photo affinity labeling may be obtained from functional studies on intact tissues.
NIOSH-Author; Muscle-contraction; Synergism; Clinical-techniques; Physiological-chemistry; Pharmacodynamics; Biological-effects; Neurophysiology; Neuromuscular-system; Biochemistry
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