Sodium nitroprusside relaxes goat coronary artery through activation of calcium-dependent K+ channels.
In the present investigation we have examined the hypothesis that calcium-dependent K+ channels (K(Ca)) are involved in the sodium nitroprusside (SNP)-induced vasodilatation of goat coronary artery. SNP (10(-9)-3 x 10(-6) M), added cumulatively, relaxed K+ (30 mM)-contracted coronary artery ring segments in a concentration-dependent manner with an EC50 of 1.32 x 10(-7) M (95% CL, 0.93-1.86 x 10(-7) M; n = 21). K(Ca) blocker, tetraethyl ammonium (1 mM) caused a rightward shift in the concentration-response curve of SNP with a corresponding increase in EC50 (1.62 x 10(-6) M; 95% CL, 0.44-6.02 x 10(-6) M, n = 4) of nitro vasodilator. Lowering of extra cellular Ca2+ in the physiological saline solution to 1/4 of normal selectively attenuated the vasorelaxant response of SNP, thereby causing an increase in its EC50 (2.4 x 10(-6) M; 95% CL, 1.23-4.68 x 10(-6) M, n = 4). Exposure of the tissues to high K+ (80 mM) solution, a protocol adopted to reduce the K+ gradient across the cell membrane, markedly inhibited the coronary artery relaxations induced by SNP (EC50, 2.54 x 10(-6) M; 95% CL, 1.31-4.91 x 10(-6) M, n = 4), when compared with tissues contracted with low K+ (30 mM) solution (EC50 7.9 x 10(-8); 95% CL, 4.4 x 10(-8)-1.44 x 10(-7) M, n = 6). The results suggested that a major component of SNP-induced relaxation of goat coronary artery was mediated by K(Ca) channels.
Deka
Dilip K
DK
Indian Veterinary Research Institute, Izatnagar, Bareilly, India. drdilipdeka@rediffmail.com
Ravi Prakash
Vellanki
V
Mishra
Santosh K
SK
D000818:Animals; D017609:Barium Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D003331:Coronary Vessels / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006041:Goats; D066298:In Vitro Techniques; D008751:Methylene Blue / Q000494:pharmacology; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects*
D017609:Barium Compounds; D002712:Chlorides; D020030:Nitric Oxide Donors; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; C024986:barium chloride; D009599:Nitroprusside; D011189:Potassium Chloride; D002118:Calcium; D008751:Methylene Blue