Lithium activates mammalian Na+/H+ exchangers: isoform specificity and inhibition by genistein.
Replacement of external NaCl with LiCl induced cytoplasmic alkalinization in CCL-39 cells and rat L6 myoblasts expressing the endogenous Na+/H+ exchanger isoform NHE1. This Li+-induced alkalinization is due to activation of the Na+/H+ exchanger because it was completely inhibited by 100 microM ethylisopropylamiloride (apparent Kd=1 microM) and because it did not occur in exchanger-deficient PS120 cells. The effect of Li+ was not mimicked by Na+, K+, Cs+ and choline+. Li+ caused cytoplasmic alkalinization in PS120 cells expressing NHE1 or NHE2, but not NHE3, when Li+ was added to cells at a concentration high enough to saturate their external transport sites as predicted from Li+ affinities. Li+ did not induce phosphatidylinositol (PI) turnover or intracellular Ca2+ mobilization. Li+-induced alkalinization was not affected by protein kinase C down-regulation, loss of glycogen synthase kinase 3beta caused by antisense oligonucleotide treatment, or pretreatment with calphostin C, pertussis toxin, MEK inhibitor PD98059 and PI3-kinase inhibitor LY294002. However, it was markedly suppressed by the tyrosine kinase inhibitor genistein (10 microM). Thus, externally added Li+ activates NHE1 and NHE2 via a mechanism possibly involving a tyrosine kinase, causing an increase in cytoplasmic pH that could potentially affect various cell functions.
Kobayashi
Y
Y
Department of Molecular Physiology, National Cardiovascular Center Research Institute, Suita, Osaka, Japan.
Pang
T
T
Iwamoto
T
T
Wakabayashi
S
S
Shigekawa
M
M
D000468:Alkalies / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D003593:Cytoplasm / Q000201:enzymology; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology; D019833:Genistein / Q000494:pharmacology*; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology*; D008168:Lung / Q000166:cytology; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000201:enzymology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D012867:Skin / Q000166:cytology; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013379:Substrate Specificity
D000468:Alkalies; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D017923:Sodium-Hydrogen Exchangers; D006859:Hydrogen; D008094:Lithium; D012964:Sodium; D019833:Genistein; D011505:Protein-Tyrosine Kinases