Vasodilator efficacy of nitric oxide depends on mechanisms of intracellular calcium mobilization in mouse aortic smooth muscle cells.
OBJECTIVE
Reduction of intracellular calcium ([Ca(2+)](i)) in smooth muscle cells (SMCs) is an important mechanism by which nitric oxide (NO) dilates blood vessels. We investigated whether modes of Ca(2+) mobilization during SMC contraction influenced NO efficacy.


METHODS
Isometric contractions by depolarization (high potassium, K(+)) or alpha-adrenoceptor stimulation (phenylephrine), and relaxations by acetylcholine chloride (ACh), diethylamine NONOate (DEANO) and glyceryl trinitrate (GTN) and SMC [Ca(2+)](i) (Fura-2) were measured in aortic segments from C57Bl6 mice.


RESULTS
Phenylephrine-constricted segments were more sensitive to endothelium-derived (ACh) or exogenous (DEANO, GTN) NO than segments contracted by high K(+) solutions. The greater sensitivity of phenylephrine-stimulated segments was independent of the amount of pre-contraction, the source of NO or the resting potential of SMCs. It coincided with a significant decrease of [Ca(2+)](i), which was suppressed by sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA) inhibition, but not by soluble guanylyl cylase (sGC) inhibition. Relaxation of K(+)-stimulated segments did not parallel a decline of [Ca(2+)](i). However, stimulation (BAY K8644) of L-type Ca(2+) influx diminished, while inhibition (nifedipine, 1-100 nM) augmented the relaxing capacity of NO.


CONCLUSIONS
In mouse aorta, NO induced relaxation via two pathways. One mechanism involved a non-cGMP-dependent stimulation of SERCA, causing Ca(2+) re-uptake into the SR and was prominent when intracellular Ca(2+) was mobilized. The other involved sGC-stimulated cGMP formation, causing relaxation without changing [Ca(2+)](i), presumably by desensitizing the contractile apparatus. This pathway seems related to L-type Ca(2+) influx, and L-type Ca(2+) channel blockers increase the vasodilator efficacy of NO.
Division of Pharmacology, University of Antwerp, Antwerp, Belgium.
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CE
Van Hove
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C
Van der Donckt
A G
AG
Herman
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H
Bult
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P
Fransen
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology; D006152:Cyclic GMP / Q000502:physiology; D006834:Hydrazines / Q000494:pharmacology; D066298:In Vitro Techniques; D042541:Intracellular Space / Q000378:metabolism; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction; D009131:Muscle, Smooth, Vascular / Q000378:metabolism / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism / Q000502:physiology*; D009569:Nitric Oxide / Q000502:physiology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D005996:Nitroglycerin / Q000494:pharmacology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000502:physiology; D014664:Vasodilation
D020746:Calcium Channels, L-Type; D006834:Hydrazines; D020030:Nitric Oxide Donors; D009569:Nitric Oxide; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D005996:Nitroglycerin; D006152:Cyclic GMP; D000109:Acetylcholine; D002118:Calcium