ACTIVATION OF NA+ H+ EXCHANGER BY HEPATOCYTE - GROWTH-FACTOR IN HEPATOCYTES/

The effect of the hepatocyte growth factor (HGF) on the Na+/H+ exchang er was studied using primary cultured hepatocytes, HGF induced intrace llular pH (pHi) elevation of 0.10 pH units in hepatocytes cultured for 4 to 7 hours; the response was lower after other culture periods, Eve n with the same culture period, intercellular heterogeneity was found in the responsiveness to HGF. This heterogeneity may be partially acco unted for by the weak but significant correlation observed between the basal pHi level and the degree of pHi elevation caused by HGF in hepa tocytes. The pHi elevation caused by HGF was blocked on pretreatment o f the hepatocytes with amiloride, suggesting that HGF activates the Na +/H+ exchanger. This hypothesis was confirmed by the fact that HGF inc reased the initial rapid rate of cell alkalization of acid-loaded hepa tocytes, The tyrosine kinase inhibitor, genistein, also blocked the el evation, consistent with the fact that HGF receptor/c-met has a tyrosi ne kinase domain. To clarify the signal transduction pathway from tyro sine kinase to the Na+/H+ exchanger, we examined the effects of inhibi tors of other kinases (H-7, H-8, and W-7) On the HGF-induced pHi eleva tion and found that only W-7 blocked it. This pHi elevation was also p revented on preincubation of the hepatocytes with thapsigargin, which blocks the calcium response caused by HGF. These results suggest that HGF activates the Na+/H+ exchanger in hepatocytes through a tyrosine k inase-calcium/calmodulin-dependent pathway.