Mishra R, Rao V, Ta R, Shobeiri N, Hill CE. Mg 2ϩ -and MgATP-inhibited and Ca 2ϩ /calmodulin-sensitive TRPM7-like current in hepatoma and hepatocytes. Am J Physiol Gastrointest Liver Physiol 297: G687-G694, 2009. First published August 6, 2009 doi:10.1152/ajpgi.90683.2008.-Although understood to be ubiquitously expressed, the functional identification and significance of Mg 2ϩ -inhibited, nonspecific cation currents has been established in only a few cell types. Here we identified an outwardly rectifying nonspecific cation current in quiescent rat hepatocytes and the proliferating and polarized rat hepatoma, WIF-B. Under whole cell recording conditions in which cells were bathed and dialyzed with Nagluconate solutions, the latter Ca 2ϩ and Mg 2ϩ free, current reversed close to 0 mV, was time independent, and was greater than 10 times higher at ϩ120 mV compared with Ϫ120 mV. Outward current at Ϫ120 mV developed slowly, from 17.7 Ϯ 10.3 pA/pF at patch rupture to 106.6 Ϯ 15.6 pA/pF at 12 min in WIF-B cells, and 4.9 Ϯ 2.7 to 20.6 Ϯ 5.6 pA/pF in rat hepatocytes. The nonspecific TRP channel inhibitor, 2-aminoethoxyphenylborate (2-APB), inhibited current (IC 50 ϭ 72 Ϯ 13 M) and caused apoptotic cell death in WIF-B cells. Rat hepatocyte survival was more resistant to 2-APB. Dialysis of WIF-B cells with physiological concentrations of Mg 2ϩ and Mg-ATP, but not ATP alone, inhibited current development, suggesting that Trpm7 rather than Trpm6 underlies this current. RT-PCR demonstrated that both Trpm6 and Trpm7 are expressed at similar levels in both cell types, suggesting that the functional differences noted are not transcript dependent. Intracellular Ca 2ϩ (IC50 ϭ 125 Ϯ 35 nM) also inhibited current development, and this could be partially relieved by the calmodulin and Ca 2ϩ /calmodulin-dependent kinase inhibitors W-7, staurosporine, or (2,3,13,17,26,35,39), and pathophysiological situations such as anoxic cell death and ischemia-reperfusion injury (1, 41). Although a role for TRPC1 in stimulus-induced Ca 2ϩ influx in the major liver epithelial cell, the hepatocyte, has been suggested (5), and both TRPM6 and TRPM7 are expressed in relatively high amounts in liver tissue (7, 9, 22), Mg 2ϩ -sensitive nonselective cation currents have not been demonstrated in these cells. Nevertheless, 2-aminoethoxyphenylborate (2-APB), albeit a relatively nonspecific inhibitor of TRPM and TRPC channels and other transporters, inhibited bile generation in perfused rat livers (10), and reduced hepatic store-operated Ca 2ϩ current and ischemia-reperfusion injury (15,27).TRPM7 currents are outwardly rectifying and exhibit very small inward currents under divalent-free intracellular recording conditions due to block of inward current by external Mg 2ϩ (26, 34). These currents develop over the course of minutes following the initiation of intracellular dialysis due to the dilution of cytosolic Mg 2ϩ . Dialysis with Mg 2ϩ -containing solutions also induces a slow inactivation, or "rundown," of TRPM7 current [IC 50 0.1-0.7 mM (26,31,40)]. T...