Mechanisms involved in the relaxation of bovine aortic endothelial cells

Abstract

The importance of endothelial cell contraction in the regulation of vascular biology is being increasingly recognized. Our group has demonstrated that reactive oxygen species, particularly hydrogen peroxide, which are released in pathological conditions such as ischemia-reperfusion, are able to induce contraction in bovine aortic endothelial cells (BAEC). The cGMP-dependent relaxation of contractile cells depends on the ability of the cyclic nucleotide to interfere with intracellular calcium; however, this is not the only mechanism involved. The present experiments were designed to analyse the mechanism by which cGMP induces relaxation in BAEC. Sodium nitroprusside (SNP), an activator of soluble guanylate cyclase, as well as atrial natriuretic (ANP) and C-type natriuretic (CNP) peptides, activators of particulate guanylate cyclase, blunted the hydrogen peroxide-induced contraction of BAEC and myosin light chain phosphorylation. The inhibitory effect was more marked with SNP and CNP than with ANP, and the action of SNP and CNP were partially reversed by blocking soluble and particulate guanylate cyclases, respectively. Dibutyryl cGMP (db-cGMP), a cGMP analogue, mimicked the effect of SNP and CNP. Cyclic GMP-dependent protein kinase (cGK) protein levels and activity were measured. Hydrogen peroxide induced a significant reduction in cGK activity without any change in protein level. This effect was completely reversed by preincubation with db-cGMP. Calyculin A, a myosin light chain phosphatase inhibitor, prevented the cGMP-induced relaxation of BAEC. SNP, CNP and db-cGMP also partially prevented the hydrogen peroxide-induced increase in intracellular calcium levels. Catalase completely blocked this effect. In summary, the present results support a role for those metabolites which activate guanylate cyclases in the relaxation of BAEC, and suggest that the cGMP-induced BAEC relaxation could be due, at least partially, to the stimulation of cGK and/or myosin light chain phosphatase activity, and to calcium blockade.