TRANSFORMING GROWTH FACTOR(BETA-1) INCREASES THE NUMBER OF APOPTOTIC BODIES AND DECREASES INTRACELLULAR PH IN ISOLATED PERIPORTAL AND PERIVENULAR RAT HEPATOCYTES

Transforming growth factor beta 1 (TGF(beta 1)) is involved in promoti ng cell death by apoptosis in the liver, whereas the activation of Na/H+ exchanger has been related to cell proliferation. The aim of this study was to gain information on the effects of TGF(beta 1) on intrace llular pH and Na+/H+ exchange activity in isolated periportal (PP) and perivenular (PV) rat hepatocytes using the pH-sensitive dye BCECF in a perfused subconfluent hepatocyte monolayer. Steady-state intracellul ar pH (pH(i)) in a bicarbonate-free solution (HEPES) were 7.17 +/- 0.0 31 in PP and 7.15 +/- 0.041 in PV cells. Treatment with TGF(beta 1) (1 20 pmol/L) for 7 hours increased the number of apoptotic bodies by 25% and 38%, and decreased steady-state pH(i) to 7.11 +/- 0.018 (P = .05) and to 7.07 +/- 0.021 (P < .02), respectively, in PP and PV hepatocyt es. In HEPES, cells recovered from an acid load, extruding protons at a rate (J(H)) of 4.85 +/- 1.01 mmol/L/min in PP cells and of 4.91 +/- 0.99 mmol/L/min in PV hepatocytes. This recovery appeared amiloride in hibitable (1 mmol/L). Culture with TGF(beta 1) for 7 hours induced (in HEPES) a decrease of pH(i) recovery rate from an acid load more in PV (by 46%) than in PP hepatocytes (by 35%, P < .05). Acute administrati on of epidermal growth factor (EGF) (10 to 100 ng/mL) induced an incre ase in Na+/H+ exchange activity by 32% and 27%, respectively, in PP an d PV cells compared with controls. In contrast, in cells cultured for 7 hours with 120 pmol/L TGF beta(1), the acute administration of EGF s lightly increased Na+/H+ exchange activity (by 18% P < .05) only in PP cells, This study demonstrates that pH(i) and Na+/H+ exchange activit y are decreased by TGF(beta 1), which increases the number of apoptoti c bodies in periportal and perivenular rat hepatocyte primary cultures .