Activation of Na+/H+ exchanger by hepatocyte growth factor in hepatocytes

The effect of the hepatocyte growth factor (HGF) on the Na+/H+ exchanger was studied using primary cultured hepatocytes. HGF induced intracellular pH (pHi) elevation of 0.10 pH units in hepatocytes cultured for 4 to 7 hours; the response was lower after other culture periods. Even with the same culture period, intercellular heterogeneity was found in the responsiveness to HGF. This heterogeneity may be partially accounted for by the weak but significant correlation observed between the basal pHi level and the degree of pHi elevation caused by HGF in hepatocytes. The pHi elevation caused by HGF was blocked on pretreatment of the hepatocytes with amiloride, suggesting that HGF activates the Na+/H+ exchanger. This hypothesis was confirmed by the fact that HGF increased the initial rapid rate of cell alkalization of acid-loaded hepatocytes. The tyrosine kinase inhibitor, genistein, also blocked the elevation, consistent with the fact that HGF receptor/c-met has a tyrosine kinase domain. To clarify the signal transduction pathway from tyrosine kinase to the Na+/H+ exchanger, we examined the effects of inhibitors of other kinases (H-7, H-8, and W-7) on the HGF-induced pHi elevation and found that only W-7 blocked it. This pHi elevation was also prevented 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 kinase-calcium/calmodulin-dependent pathway.