EVIDENCE FOR 5-HT1D-BETA BUT NOT 5-HT1D-ALPHA RECEPTOR SUBTYPE EXPRESSION IN CANINE LARGE CORONARY-ARTERIES AND SAPHENOUS-VEIN

Objective: 5-Hydroxytryplamine(ID) (5-HTID) receptors are believed to play a major role in the vasoconstriction of vascular smooth ID muscle in human coronary arteries. However, unequivocal evidence as to which subtype of this receptor (5-HTIDe or 5-HTID beta) is involved in thes e vasoconstrictory effects is lacking. The aim of this study was to id entify in the dog the 5-HTID receptor subtype encoding mRNAs expressed in several large coronary arteries and in the saphenous vein. Methods : Degenerate oligonucleotide primers that selectively recognized only mammalian 5-HTID alpha and 5-HTID beta receptor sequences were used in RT-PCR experiments to study a 5-HTID receptor subtype expression in e ndothelium-denuded saphenous vein and large coronary arteries from bea gle and alsatian dogs. Resulting PCR products were analysed and identi fied by Southern blots and sequencing. Results: An identical PCR produ ct whose sequence closely resembles that of the human 5-HTID beta rece ptor (98% amino acid identity) was obtained from reverse-transcribed R NA isolated from either saphenous vein or coronary arteries, irrespect ive of dog race. Absence of 5-HTID alpha expression was confirmed by S outhern blot analysis. Control experiments using canine genomic DNA as template illustrated, nonetheless, that the primers chosen could ampl ify both 5-HTID alpha and 5-HTID beta sequences. Conclusion: Using RT- PCR, we isolated from dog vascular smooth muscle a cDNA 5HT(ID beta) r eceptor. We illustrated fragment whose nucleotide sequence would encod e a previously-unreported canine homologue of the 5-HT that this subty pe is the only 5-HTID receptor subtype expressed in dog saphenous vein and large coronary arteries. The implications of these findings are d iscussed in light of results from functional studies of 5-HTI-like rec eptor-mediated effects in these canine blood vessels.