Chloride, not sodium, stimulates expression of the gamma subunit of Na/K-ATPase and activates JNK in response to hypertonicity in mouse IMCD3 cells.
Hypertonicity induced by NaCl, but not by urea or mannitol, up-regulates expression of the gamma subunit of Na/K-ATPase in cells of the murine inner medullary collecting duct line (IMCD3) by activation of the Jun kinase 2 (JNK2) pathways. We examined the ionic mediators of the osmosensitive response. An increase in osmolality to 550 milliosmoles per kg of water (mosmol/kgH2O) for 48 h by replacement of NaCl with choline chloride did not prevent the up-regulation of the gamma subunit. Neither Na+ ionophores nor inhibitors of cellular Na+ uptake altered the up-regulation of the gamma subunit or JNK activation. Changes in cell cation concentrations driven by incubation in low-K+ medium were effective in up-regulating the alpha1 subunit of Na/K-ATPase but did not have any effect on the gamma subunit. The replacement of NaCl with choline chloride did not down-regulate gamma-subunit expression in cells adapted to hypertonicity. In contrast, the replacement of NaCl with sodium acetate, or pretreatment of cells with the Cl- channel inhibitor 5-nitro-2-(3-phenylpropyl-amino)benzoic acid (NPPB) completely blocked gamma-subunit up-regulation, inhibited JNK activation, and caused a significant decrement in cell survival in hypertonic but not isotonic conditions. In adapted cells, replacement of 300 mosmol/kgH2O NaCl with sodium acetate resulted in down-regulation of the gamma subunit. In conclusion, we describe a Na+-independent, Cl--dependent mechanism for hypertonicity-mediated activation of the JNK and the subsequent synthesis of the gamma subunit of Na/K-ATPase, which are necessary for cellular survival in these anisotonic conditions.
Department of Medicine, Division of Renal Disease and Hypertension, University of Colorado Health Sciences Center, 4200 East 9th Avenue, Denver 80262, USA.
Juan M
JM
Capasso
Christopher J
CJ
Rivard
Laura M
LM
Enomoto
Tomas
T
Berl
D000818:Animals; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009994:Osmolar Concentration; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D002712:Chlorides; D004791:Enzyme Inhibitors; D012964:Sodium; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D000254:Sodium-Potassium-Exchanging ATPase