Osmo-mechanically sensitive phosphatidylinositol signaling regulates a Ca2+ influx channel in renal epithelial cells.
Regulation of dihydropyridine (nifedipine)-sensitive calcium influx was studied in rabbit culture proximal tubule cells using the fura 2 fluorescence ratio technique. "Osmo-mechanically induced" swelling of cells by exposure to hypotonic medium (220 mosmol/kgH2O) caused a rapid rise in intracellular calcium that was predominantly due to influx of calcium via both dihydropyridine-sensitive (nifedipine-sensitive) and -insensitive calcium influx pathways. The dihydropyridine-sensitive pathway was regulated, in part, by the phosphatidylinositol signaling pathway. Inhibition of phospholipase C by treatment with 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC), inhibition of protein kinase C (PKC) by staurosporine, or long-term (24 h) treatment with phorbol 12-myristate 13-acetate (PMA) to downregulate PKC abolished most of the osmo-induced, dihydropyridine-sensitive calcium influx signal. Short-term (seconds) PMA treatment to activate PKC produced a marked stimulation of both dihydropyridine-sensitive and -insensitive calcium influx in isotonic (2- to 3-fold stimulation) and hypotonic (5-fold stimulation) conditions. In contrast, elevation of adenosine 3',5'-cyclic monophosphate (cAMP) by treatment with forskolin or inhibition of protein kinase A (PKA) by treatment with the cAMP analog, Rp-8-CPT-cAMPS (the Rp diastereoisomer of adenosine 3',5'-cyclic monophosphothionate), had little or no influence on calcium influx, including dihydropyridine-sensitive calcium influx. It is concluded that osmo-mechanical stress activates a dihyropyridine-sensitive calcium influx pathway that is predominantly regulated via the phosphatidylinositol signaling pathway and PKC and not through the cAMP/PKA signaling pathway.
O'Neil
R G
RG
Department of Integrative Biology, University of Texas-Houston Health Science Center 77030, USA.
Leng
L
L
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D020746:Calcium Channels, L-Type; D002219:Carbamates / Q000494:pharmacology; D002478:Cells, Cultured; D004095:Dihydropyridines / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000502:physiology*; D007700:Kinetics; D008297:Male; D009543:Nifedipine / Q000494:pharmacology; D048448:Phenylcarbamates; D010716:Phosphatidylinositols / Q000378:metabolism*; D011817:Rabbits; D015398:Signal Transduction; D019311:Staurosporine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014882:Water-Electrolyte Balance
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002219:Carbamates; D004095:Dihydropyridines; D004791:Enzyme Inhibitors; D048448:Phenylcarbamates; D010716:Phosphatidylinositols; C025508:2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate; C038806:1,4-dihydropyridine; D019311:Staurosporine; D009543:Nifedipine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium