HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 289/1/C68    most recent 00631.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (9) Citing Articles via Google Scholar Google Scholar Articles by Ciano-Oliveira, C. D. Articles by Kapus, A. Search for Related Content PubMed PubMed Citation Articles by Ciano-Oliveira, C. D. Articles by Kapus, A.

MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Is myosin light-chain phosphorylation a regulatory signal for the osmotic activation of the Na⁺-K⁺-2Cl^– cotransporter?

¹Department of Surgery, The Toronto General Hospital and University Health Network, Toronto, Ontario, Canada; and ²Department of Biological Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Japan

Submitted 22 December 2004 ; accepted in final form 16 February 2005

Myosin light-chain (MLC) kinase (MLCK)-dependent increase in MLC phosphorylation has been proposed to be a key mediator of the hyperosmotic activation of the Na⁺-K⁺-2Cl^– cotransporter (NKCC). To address this hypothesis and to assess whether MLC phosphorylation plays a signaling or permissive role in NKCC regulation, we used pharmacological and genetic means to manipulate MLCK, MLC phosphorylation, or myosin ATPase activity and followed the impact of these alterations on the hypertonic stimulation of NKCC in porcine kidney tubular LLC-PK1 epithelial cells. We found that the MLCK inhibitor ML-7 suppressed NKCC activity independently of MLC phosphorylation. Notably, ML-7 reduced both basal and hypertonically stimulated NKCC activity without influencing MLC phosphorylation under these conditions, and it inhibited NKCC activation by Cl^– depletion, a treatment that did not increase MLC phosphorylation. Furthermore, prevention of the osmotically induced increase in MLC phosphorylation by viral induction of cells with a nonphosphorylatable, dominant negative MLC mutant (AA-MLC) did not affect the hypertonic activation of NKCC. Conversely, a constitutively active MLC mutant (DD-MLC) that mimics the diphosphorylated form neither stimulated isotonic nor potentiated hypertonic NKCC activity. Furthermore, a depolarization-induced increase in endogenous MLC phosphorylation failed to activate NKCC. However, complete abolition of basal MLC phosphorylation by K252a or the inhibition of myosin ATPase by blebbistatin significantly reduced the osmotic stimulation of NKCC without suppressing its basal or Cl^– depletion-triggered activity. These results indicate that an increase in MLC phosphorylation is neither a sufficient nor a necessary signal to stimulate NKCC in tubular cells. However, basal myosin activity plays a permissive role in the optimal osmotic responsiveness of NKCC.

proline-alanine-rich STE20-related kinase

This article has been cited by other articles:

				S. C. Chow, L. Y. Ching, A. M. F. Wong, and C. K. C. Wong Cloning and regulation of expression of the Na+-Cl--taurine transporter in gill cells of freshwater Japanese eels J. Exp. Biol., October 15, 2009; 212(20): 3205 - 3210. [Abstract] [Full Text] [PDF]

				J. N. Chabwine, K. Talavera, L. Verbert, J. Eggermont, J.-M. Vanderwinden, H. De Smedt, L. Van Den Bosch, W. Robberecht, and G. Callewaert Differential contribution of the Na+-K+-2Cl- cotransporter NKCC1 to chloride handling in rat embryonic dorsal root ganglion neurons and motor neurons FASEB J, April 1, 2009; 23(4): 1168 - 1176. [Abstract] [Full Text] [PDF]

				A. C. P. Thirone, P. Speight, M. Zulys, O. D. Rotstein, K. Szaszi, S. F. Pedersen, and A. Kapus Hyperosmotic stress induces Rho/Rho kinase/LIM kinase-mediated cofilin phosphorylation in tubular cells: key role in the osmotically triggered F-actin response Am J Physiol Cell Physiol, March 1, 2009; 296(3): C463 - C475. [Abstract] [Full Text] [PDF]

				E. K. Hoffmann, I. H. Lambert, and S. F. Pedersen Physiology of Cell Volume Regulation in Vertebrates Physiol Rev, January 1, 2009; 89(1): 193 - 277. [Abstract] [Full Text] [PDF]

				E. K. Hoffmann and S. F. Pedersen Shrinkage insensitivity of NKCC1 in myosin II-depleted cytoplasts from Ehrlich ascites tumor cells Am J Physiol Cell Physiol, May 1, 2007; 292(5): C1854 - C1866. [Abstract] [Full Text] [PDF]

				L. Fan, A. Sebe, Z. Peterfi, A. Masszi, A. C.P. Thirone, O. D. Rotstein, H. Nakano, C. A. McCulloch, K. Szaszi, I. Mucsi, et al. Cell Contact-dependent Regulation of Epithelial-Myofibroblast Transition via the Rho-Rho Kinase-Phospho-Myosin Pathway Mol. Biol. Cell, March 1, 2007; 18(3): 1083 - 1097. [Abstract] [Full Text] [PDF]