Effect of the Na+/H+ antiport inhibitor Hoe 694 on the angiotensin II-induced vascular smooth muscle cell growth.

1. Hoe 694 (3-methylsulphonyl-4-piperidinobenzoyl)guanidine methanesulphonate) was characterized as a new, potent, non-amiloride inhibitor of the Na+/H+ exchanger. In order to elucidate the role of the Na+/H+ exchanger isoform 1 (NHE-1) in the regulation of vascular smooth muscle cell growth, we investigated the effects of different amiloride analogues and of Hoe 694 on angiotensin II-induced cell growth. Since intracellular pH, the intracellular free Ca2+ concentration and the expression of the transcription factor c-fos seem to be involved in the regulation of cell growth, the effects of the amiloride analogues and Hoe 694 on the angiotensin II-induced changes in these three parameters were examined. 2. Measurement of cytosolic Ca2+ and pH in cell monolayers was performed using fura-2/AM and BCECF/AM, respectively. The effect of angiotensin II on cell growth was examined using (1) [3H]-thymidine incorporation, (2) the bromo-2-deoxyuridine (BrdU) immunfluorescence assay, (3) the colorimetric determination of cell mitochondrial dehydrogenase activity and (4) determination of cell number. Total RNA was extracted from cells by the guanidinium isothiocyanate/CsCl procedure. The expression of c-fos was quantitated by Northern blotting. 3. Various amiloride analogues inhibited the angiotensin II-induced stimulation of the Na+/H+ exchanger, the increase in cytosolic Ca2+ and cell growth but not the induction of c-fos mRNA. Hoe 694 (1-25 microM) dose-dependently inhibited the angiotensin II-induced stimulation of the Na+/H+ exchanger but had no significant effects on cytosolic Ca2+, c-fos mRNA levels or cell growth. 4. Our findings support the concept that activation of the Na+/H+ exchanger is not essential for angiotensin II-induced vascular smooth muscle cell growth.