Vasodilator efficacy of nitric oxide depends on mechanisms of intracellular calcium mobilization in mouse aortic smooth muscle cells
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences. Pharmacy
Faculty of Medicine and Health Sciences
British journal of pharmacology. - London
, p. 920-930
University of Antwerp
Background and purpose: Reduction of intracellular calcium ([Ca2+]i) in smooth muscle cells (SMCs) is an important mechanism by which nitric oxide (NO) dilates blood vessels. We investigated whether modes of Ca2+ mobilization during SMC contraction influenced NO efficacy. Experimental approach: Isometric contractions by depolarization (high potassium, K+) or α-adrenoceptor stimulation (phenylephrine), and relaxations by acetylcholine chloride (ACh), diethylamine NONOate (DEANO) and glyceryl trinitrate (GTN) and SMC [Ca2+]i (Fura-2) were measured in aortic segments from C57Bl6 mice. Key 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 [Ca2+]i, which was suppressed by sarcoplasmic reticulum (SR) Ca2+ ATPase (SERCA) inhibition, but not by soluble guanylyl cylase (sGC) inhibition. Relaxation of K+-stimulated segments did not parallel a decline of [Ca2+]i. However, stimulation (BAY K8644) of L-type Ca2+ influx diminished, while inhibition (nifedipine, 1100 nM) augmented the relaxing capacity of NO. Conclusions and implications: In mouse aorta, NO induced relaxation via two pathways. One mechanism involved a non-cGMP-dependent stimulation of SERCA, causing Ca2+ re-uptake into the SR and was prominent when intracellular Ca2+ was mobilized. The other involved sGC-stimulated cGMP formation, causing relaxation without changing [Ca2+]i, presumably by desensitizing the contractile apparatus. This pathway seems related to L-type Ca2+ influx, and L-type Ca2+ channel blockers increase the vasodilator efficacy of NO.