Ca2+-sensitivity and cGMP-independent effects of NO in vascular smooth muscle.
The effects of NO on Ca2+-sensitivity of vascular smooth muscle (VSM) myofilaments have been the focus of this study. Simultaneous measurements of [Ca2+]i and force were carried out in rat tail artery segments. NO, 10(-7) M, evoked a transient decrease in [Ca2+]i accompanied by sustained relaxation (45.3+/-6.3 vs. 69.45+/-7.2%, P<0.05, respectively) of VSM precontracted with K+ (70 mM), suggesting a decrease in Ca2+-sensitivity of VSM. This decrease in Ca2+-sensitivity was completely abolished by preincubation of VSM with ODQ (10(-6) M) (63.9+/-7.8% for [Ca2+]i vs. 20.5+/-8.4% for relaxation, P<0.05). Ca2+-presensitization of VSM myofilaments with PE (10(-6) M) decreased the efficacy of NO to relax VSM (44.25+/-6.9% vs. 69.45+/-7.2%, P<0.05), but increased its ability to lower [Ca2+]i (70.5+/-6.8% vs. 45.3+/-6.3%, P<0.05). Application of DTT (10(-3) M) together with ODQ (10(-6) M) to subtract possible cGMP-independent effects revealed the total suppression of both the relaxant responses and [Ca2+]i of VSM under high-K+ preactivation of VSM. The data indicate that NO not only relaxes VSM and lowers [Ca2+]i in K+-preactivated VSM, but also decreases Ca2+-sensitivity of VSM myofilaments and these effects are strongly cGMP-dependent. In PE-induced contractions of VSM, NO relaxed VSM of rat tail artery and lowered [Ca2+]i, but failed to reverse Ca2+-presensitized myofilaments. We suggest that alternative cGMP-independent effects of NO are primarily manifested via activation of K+-channels and inhibition of Ca2+ current rather than to affect relaxation. An importance of reduced SH-groups within VSM myoplasm for both relaxation and [Ca2+]i disposal evoked by NO is evident whatever Ca2+-mobilization pathways are involved.
Lehen'kyi
V V
VV
Department of Experimental Therapy, Institute of Pharmacology and Toxicology, 14 Ezhena Pot'e, 03057 Kyiv, Ukraine. lehenkyi_vyacheslav@yahoo.com
Zelensky
S N
SN
Stefanov
A V
AV
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006152:Cyclic GMP / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D009569:Nitric Oxide; D006152:Cyclic GMP; D002118:Calcium