Roles of Ca2+ and PKC in regulation of acid/base transport in isolated proximal tubules.
Roles of Ca2+ and protein kinase C (PKC) in the regulation of acid/base transport in isolated rabbit proximal tubules were investigated by measuring cytosolic Ca2+ concentrations ([Ca2+]i) and cell pH (pHi) with fluorescent probes. Ionomycin (0.2 microM) increased [Ca2+]i by approximately 200 nM but did not affect the basolateral Na(+)-HCO3- cotransporter. However, the apical Na+/H+ exchanger was inhibited by 50% by ionomycin, and this inhibition was abolished either by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, an intracellular Ca2+ chelator, or by KN-62, an inhibitor of calcium-calmodulin-dependent protein kinase II (CaM kinase II). On the other hand, phorbol 12-myristate 13-acetate (PMA, 0.5 microM) did not affect the apical Na+/H+ exchanger but did stimulate the basolateral Na(+)-HCO3- cotransporter by 60-80%, and this stimulation was prevented by calphostin C, an inhibitor of PKC. Consistent with the cotransporter stimulation, PMA decreased steady-state pHi in the presence of CO2/ HCO3-. These results indicate that 1) the acute increase in [Ca2+]i within physiological ranges inhibits the apical Na+/H+ exchanger, probably through mediation of CaM kinase II; and 2) the short-term PKC activation stimulates the basolateral Na(+)-HCO3- cotransporter.
Yamada
H
H
First Department of Internal Medicine, Tokyo University School of Medicine, Japan.
Seki
G
G
Taniguchi
S
S
Uwatoko
S
S
Nosaka
K
K
Suzuki
K
K
Kurokawa
K
K
D000143:Acids / Q000378:metabolism*; D000468:Alkalies / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005260:Female; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D009994:Osmolar Concentration; D011493:Protein Kinase C / Q000502:physiology*; D011817:Rabbits; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000143:Acids; D000468:Alkalies; D002352:Carrier Proteins; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers; D015759:Ionomycin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium