epidermal-growth-factor and ethylisopropylamiloride

The modulation by epidermal growth factor (EGF) of the Na+/H+ antiport in fetal and adult rat hepatocytes was studied in nominally HCO3- free solution. EGF (10 nM) activated the antiport in adult rat hepatocytes by 0.22 +/- 0.03 (mean +/- SD;n=10) pH units over basal value, measured with the fluorescent pH-sensitive intracellular probe, 2',7'-bis(carboxyethyl)-5(6)- carboxyfluorescein (BCECF). The effect of EGF was inhibited by amiloride analogue 5-(N-ethyl-N-isopropyl) amiloride (EIPA), by ouabain, inhibitor of the Na+ pump, and by erbstatin analogue, an inhibitor of the tyrosine kinase activity of the EGF receptor. The effect of EGF on Na+/H+ antiport in adult rat hepatocytes appeared to be mediated by both protein kinase C (PKC) and G protein system. No effect of EGF and phorbol 12-myristate 13-acetate, an activator of PKC, on the Na+/H+ antiport was observed in fetal hepatocytes of 20 and 22 days. A different sensitivity of the antiport to high concentrations of amiloride and EIPA suggests that altered amount of the Na+/H+ antiport units or different isoforms could be expressed in fetal compared with adult cells.

Topics: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Amiloride; Animals; Cells, Cultured; Enzyme Inhibitors; Epidermal Growth Factor; Fetus; Fluoresceins; Fluorescent Dyes; GTP-Binding Proteins; Hydroquinones; Kinetics; Liver; Ouabain; Protein Kinase C; Protein-Tyrosine Kinases; Rats; Rats, Wistar; Sodium-Hydrogen Exchangers; Tetradecanoylphorbol Acetate

Vascular smooth muscle cell proliferation has been shown to be an important factor in atheromatous plaque formation, hypertrophy associated with essential hypertension, and failure of balloon angioplasty procedures. Investigators have shown that a number of different agents stimulate vascular smooth muscle cell proliferation, including epidermal growth factor, platelet-derived growth factor, angiotensin II, and catecholamines. Previously, we have demonstrated that these agents also cause immediate changes in ion transport and second messenger generation in vascular smooth muscle cells. We have proposed that these immediate changes may be linked to each other and to cell proliferation. In contrast to the many agents that have been shown to stimulate vascular smooth muscle cell proliferation, only a few agents (e.g., heparin sodium or transforming growth factor-beta) have been shown to inhibit vascular smooth muscle cell proliferation. In the present study we have investigated whether heparin inhibits serum- or growth factor-stimulated changes in ion transport and second messenger generation in vascular smooth muscle cells. We found that heparin inhibits serum- or growth factor-stimulated Na(+)-H+ exchange in a concentration-dependent manner that is not dependent on the ability of heparin to function as an anticoagulant agent. In addition, other glycosaminoglycans were not found to be inhibitory, and the inhibitory effects of heparin were discovered to be limited to vascular smooth muscle cells. Heparin does not appear to be acting by binding to growth factors, or by directly inhibiting the Na(+)-H+ exchange protein. However, heparin did inhibit serum- or growth factor-stimulated inositol trisphosphate release and calcium mobilization.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Amiloride; Angiotensin II; Animals; Aorta, Thoracic; Carrier Proteins; Cattle; Cells, Cultured; Endothelium, Vascular; Epidermal Growth Factor; Glycosaminoglycans; Heparin; Hydrogen-Ion Concentration; Inositol; Inositol 1,4,5-Trisphosphate; Kinetics; Male; Mice; Mice, Inbred Strains; Muscle, Smooth, Vascular; Ouabain; Platelet-Derived Growth Factor; Rats; Rats, Inbred WF; Sodium; Sodium-Hydrogen Exchangers