Studies on vasorelaxation by tetrapentylammonium ions in rat aortic rings.
Tetrapentylammonium ions (TPA+) relaxed the isolated rat aortic rings precontracted with phenylephrine and high extracellular K+ in a concentration-dependent manner with respective IC50 values of 38.9 +/- 3.9 microM and 40.2 +/- 2.9 microM. Other quaternary ammonium ions with a carbon side chain of varying length did not induce relaxation. The relaxant effect of TPA+ was independent of the presence of the endothelium, and was unaffected by various putative blockers of K+ channels such as iberiotoxin (100 nM), glibenclamide (3 microM) and 4-aminopyridine (1 mM). In addition, tetrodotoxin (3 microM), indomethacin (10 microM) and methylene blue (10 microM) had no effect on the TPA+-induced relaxation. TPA+ (50 microM) and procaine (10 mM) completely abolished the phasic contractile response to caffeine in Ca2+-free solution. In the absence of extracellular Ca2+, phorbol 12,13-diacetate (PDA) evoked a sustained tension and TPA+ concentration-dependently reduced the contraction with IC50 of 30.7 +/- 3.1 microM. TPA+ reduced the sustained tension of the similar magnitude induced by phenylephrine, 60 mM K+ and active phorbol ester with similar potencies. These results indicate that TPA+ could act as a non-selective relaxant in arterial smooth muscle. This vasorelaxant effect is unique for TPA+ since other quaternary ammonium ions did not show the similar action in the rat aorta.
Huang
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Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, NT, Hong Kong. b538708@mailserv.cuhk.edu.hk
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002412:Cations; D066298:In Vitro Techniques; D017136:Ion Transport; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D026902:Potassium Channel Blockers; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects*
D002412:Cations; D010703:Phorbol Esters; D026902:Potassium Channel Blockers; D000644:Quaternary Ammonium Compounds; D010656:Phenylephrine; C008874:phorbol-12,13-diacetate; C027435:tetrapentylammonium; D002118:Calcium