Knight, Gilliam Elizabeth; (1995) A comparative study of purinoceptors in some invertebrates and vertebrates. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The main objective of this thesis has been to identify and characterise responses to purine compounds in a variety of invertebrates and lower vertebrates, and to examine whether they act on receptors that resemble the purinoceptor subtypes established in mammals. Tissues were chosen largely from the gastrointestinal or cardiovascular systems. In mammalian systems adenosine and adenosine 5'-triphosphate (ATP) activate separate classes of purinoceptors; this also appears to be true for tissues in most invertebrate groups, but there are exceptions, for instance the hearts of the snail Helix aspersa, and slug Arion ater, and the snail rectum all possess purinoceptors that do not appear to distinguish the purine nucleosides from nucleotides. However, the discriminating effect of glibenclamide revealed the presence of P1- and P2-like purinoceptors in the gastric ligament of the starfish Asterias rubens. The evolutionary advancement from invertebrates to lower vertebrates was reflected in the greater degree of purinoceptor differentiation. The stomach of the stickleback Gasterosteus aculeatus, exhibited a P2Y-purinoceptor, while there is a P2X-purinoceptor in the intestine, both mediating contraction; both expressed a P1-purinoceptor, although no subtypes equivalent to those from mammals could be distinguished. Adenosine dilated the aorta of the frog Rana temporaria, via a receptor resembling the A3 subtype defined in mammals; a P2X-purinoceptor mediating constriction was identified in this vessel comparable to that known in mammalian vessels. A P1-purinoceptor mediating vasodilatation was also found on the aorta of the garter snake Thamnophis sirtalis parietalis together with multiple P2-purinoceptors, P2X- and P2Y-receptors, both mediating constriction.

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