Angiotensin-II-dependent NHE1 activation in human monocytes

Abstract 

Angiotensin II, a potent vasoconstrictor, has been demonstrated to be involved in the pathogenesis of atherosclerosis, and its complications. Na⁺/H⁺ exchanger isoform-1 (NHE1) is related to hypertension activation and can augment atherosclerosis-related functions in human monocytes. The purpose of this study is to investigate in monocytes the signal transduction pathway induced by angiotensin II, in which the Na⁺/H⁺ exchanger (NHE1) takes part. Monocytes were isolated, and intracellular pH (pHi) was measured by the use of Bis-(carboxyethyl)-5(6)-carboxy-fluorescein acetoxymethylester. Superoxide anions were measured by nitroblue tetrazolium. Monocyte binding to laminin-1 was quantified using the myeloperoxidase assay. Angiotensin II caused a significant increase in pHi of monocytes, which indicates NHE activation. Cariporide, an NHE1 inhibitor, GF109203X, and Gö6976, inhibitors of isoforms of protein kinase C (PKC), diphenyleneiodonium chloride, the inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and N_ω-Nitro-L-arginine methyl ester hydrochloride, the inhibitor of nitric oxide (NO) synthase, reversed this effect. Moreover, it was shown that angiotensin II caused an increase in superoxide ion (O₂^−.) levels as well as an increase in monocytes' adhesion to laminin-1, in relation to controls. The use of cariporide inhibited these effects. Furthermore, angiotensin II caused an increase in pHi, which was reversed by cariporide in monocytes derived from hypertensive patients. Consequently, in human monocytes angiotensin II caused NHE1 activation through pathways involving isoforms of PKC with the participation of O₂^−. and NO. In addition, a link between angiotensin II and the atherogenic properties of monocytes was shown, where NHE1 plays a central role.

Keywords: Hypertension, atherosclerosis, reactive oxygen species, signaling, intracellular pH