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.
Capasso
Juan M
JM
Department of Medicine, Division of Renal Disease and Hypertension, University of Colorado Health Sciences Center, 4200 East 9th Avenue, Denver 80262, USA.
Rivard
Christopher J
CJ
Enomoto
Laura M
LM
Berl
Tomas
T
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