Relaxation to authentic nitric oxide and SIN-1 in rat isolated mesenteric arteries: variable role for smooth muscle hyperpolarization.
Authentic nitric oxide (NO; 0.1 - 10 micromoles) caused transient, dose-dependent relaxation of phenylephrine-induced tone without changing membrane potential in mesenteric arteries. Larger doses, above 10 micromoles, did not evoke more relaxation (maximal relaxation to 150 micromoles NO in denuded arteries, 69+/-7%, n=8) but stimulated muscle hyperpolarization (maximum 19+/-3 mV, n=5). The soluble guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 microM), abolished relaxation to low doses of NO (n=4), but did not modify hyperpolarization with higher doses of NO (n=4). The potassium channel blocker charybdotoxin (ChTX; 50 nM) abolished hyperpolarization to high doses of NO and significantly reduced the maximal relaxation (to 43+/-6%, n=4; P<0.01). ODQ and ChTX together abolished tension and membrane potential change to all doses of NO (n=4). All relaxations to 3-morpholino-sydnonimine (SIN-1; 0.01 - 10 microM) were associated with hyperpolarization. When the endothelium was intact, ChTX inhibited hyperpolarization and relaxation to SIN-1 (n=5), while iberiotoxin (IbTX; 50 nM) or 4-aminopyridine (4-AP; 500 microM) reduced relaxation by 40% and 20%, respectively and by 80% in combination (n=6 in each case). In denuded arteries, relaxation to SIN-1 was unaffected by either ChTX or ODQ alone, but abolished by the inhibitors together (n=6). Alone, 4-AP did not alter relaxation, but in the presence of ODQ it reduced the maximal response by around 45% (n=6; P<0.01). 4-AP, ODQ and IbTX together inhibited relaxation to SIN-1 by 75% (n=6; P<0.01). Therefore, cyclic guanosine 3',5'-monophosphate (cyclic GMP)-independent smooth muscle hyperpolarization, possibly involving direct activation of calcium-activated and voltage-sensitive potassium channels, contributes to relaxation evoked by authentic NO and SIN-1. However, the importance of each pathway depends on the source of NO and with SIN-1 the relative contribution from each pathway is modified by the endothelium.
Plane
F
F
Cardiovascular Research Laboratories, University of Bristol, Bristol, BS8 1TD.
Sampson
L J
LJ
Smith
J J
JJ
Garland
C J
CJ
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D018999:Charybdotoxin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008981:Molsidomine / Q000031:analogs & derivatives / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000494:pharmacology* / Q000502:physiology; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D010069:Oxadiazoles / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D026902:Potassium Channel Blockers; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014664:Vasodilation / Q000187:drug effects*
C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D004791:Enzyme Inhibitors; D020030:Nitric Oxide Donors; D010069:Oxadiazoles; D010455:Peptides; D026902:Potassium Channel Blockers; D011810:Quinoxalines; D018999:Charybdotoxin; D009569:Nitric Oxide; C002385:linsidomine; C064719:iberiotoxin; D015761:4-Aminopyridine; D008981:Molsidomine; D006162:Guanylate Cyclase