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

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal 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 Google Scholar Google Scholar Articles by Dascalu, A Articles by Korenstein, R Search for Related Content PubMed PubMed Citation Articles by Dascalu, A Articles by Korenstein, R

Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Israel.

1. The hyperosmotic activation of the Na(+)-H+ exchanger was studied in an osteoblast-like rat cell line (RCJ 1.20). The activation was monitored by recording the intracellular pH (pHi) changes employing double excitation of the pH-sensitive fluorescent dye 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM). 2. Exposure of the cells to a hyperosmotic HCO(3-)-free medium at 37 degrees C produced an initial cytosolic acidification of 0.05 pH units followed by a lag period and an alkalinization overshoot of about 0.2 pH units, without a concomitant change of the free cytosolic calcium [Ca2+]i by the use of Fura-2 calcium-sensitive probes. This response was completely inhibited by amiloride (0.33 mM) or by Na+ depletion from the external medium and insensitive to the extracellular Cl- replacement, indicating the involvement of a Na(+)-H+ exchanger in the hyperosmotic response. 3. Hyperosmotic stimuli (200 moSM sucrose) applied in the temperature range of 17-37 degrees C demonstrated a shortening of the lag period preceding alkalinization and an increased rate of proton extrusion upon temperature elevation. The biochemical reaction underlying the lag period and the proton extrusion resulted in apparent activation energies of 19 and 29 kcal mol-1, respectively, as calculated from the appropriate Arrhenius plots. 4. Stimulation of the exchanger under isosmotic conditions by 25 nM 4 beta-phorbol 12-myristate 13-acetate (PMA) and 0.1 mM vanadate resulted in an amiloride-sensitive pHi increase of about 0.08 pH units. The hyperosmotic stress was additive to the stimulatory effects of these agents, suggesting an independent hyperosmotic activation pathway. 5. The hyperosmotic activation of the Na(+)-H+ exchanger was independent of cAMP, cGMP, cytosolic Ca2+ and protein kinase C. Thus, none of the classical transduction mechanisms seem to be involved directly in the hyperosmotic activation of the antiporter. 6. The pHi response induced by the hyperosmotic stress was abolished by two calmodulin inhibitors, W-7 and chlorpromazine (50% inhibition, Ki at 28 and 20 microM, respectively), 20 microM cytochalasin B, but not by 10 microM colchicine. The results suggest the involvement of actin and calmodulin-like structural elements of the cytoskeleton in the transduction process leading to the activation of the Na(+)-H+ exchanger.

This article has been cited by other articles:

				K. H. Ahmed and B. Pelster Interdependence of Ca2+ and proton movements in trout hepatocytes J. Exp. Biol., October 1, 2007; 210(19): 3473 - 3483. [Abstract] [Full Text] [PDF]

				K. H. Ahmed, B. Pelster, and G. Krumschnabel Signalling pathways involved in hypertonicity- and acidification-induced activation of Na+/H+ exchange in trout hepatocytes J. Exp. Biol., August 15, 2006; 209(16): 3101 - 3113. [Abstract] [Full Text] [PDF]

				H. L. Ebner, A. Cordas, D. E. Pafundo, P. J. Schwarzbaum, B. Pelster, and G. Krumschnabel Importance of cytoskeletal elements in volume regulatory responses of trout hepatocytes Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2005; 289(3): R877 - R890. [Abstract] [Full Text] [PDF]

				Y. Miyata, S. Muto, S. Yanagiba, and Y. Asano Extracellular Cl- modulates shrinkage-induced activation of Na+/H+ exchanger in rat mesangial cells Am J Physiol Cell Physiol, June 1, 2000; 278(6): C1218 - C1229. [Abstract] [Full Text] [PDF]

				T. Ikeda, T. Iwamoto, S. Wakabayashi, and M. Shigekawa Regulation of the Na+/H+ exchanger in fibroblasts overexpressing the Na+/Ca2+ exchanger Am J Physiol Cell Physiol, June 1, 1998; 274(6): C1537 - C1544. [Abstract] [Full Text] [PDF]

				F. LANG, G. L. BUSCH, M. RITTER, H. VOLKL, S. WALDEGGER, E. GULBINS, and D. HAUSSINGER Functional Significance of Cell Volume Regulatory Mechanisms Physiol Rev, January 1, 1998; 78(1): 247 - 306. [Abstract] [Full Text] [PDF]

				M. Soleimani, G. Singh, J. H. Dominguez, and R. L. Howard Long-term High Osmolality Activates Na+-H+ Exchange and Protein Kinase C in Aortic Smooth Muscle Cells Circ. Res., April 1, 1995; 76(4): 530 - 535. [Abstract] [Full Text]