|
|
|
|
|
|
|
||
J. Gen. Physiol.,
Volume 110, Number 5, November 1, 1997 629-639
Dependence of Na-H Exchange in Barnacle Muscle
Fibers under Normotonic and Hypertonic Conditions
From the Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520
We previously showed that shrinking a barnacle muscle fiber (BMF) in a hypertonic solution (1,600 mosM/kg) stimulates an amiloride-sensitive Na-H exchanger. This activation is mediated by a G protein and requires intracellular Cl
. The purpose of the present study was to determine (a) whether Cl plays a role in the activation of Na-H exchange under normotonic conditions (975 mosM/kg), (b) the dose dependence of [Cl]i for
activation of the exchanger under both normo- and hypertonic conditions, and (c) the relative order of the Cl-
and G-protein-dependent steps. We acid loaded BMFs by internally dialyzing them with a pH-6.5 dialysis fluid containing no Na+ and 0-194 mM Cl. The artificial seawater bathing the BMF initially contained no Na+. After dialysis was halted, adding 50 mM Na+ to the artificial seawater caused an amiloride-sensitive pHi increase under both
normo- and hypertonic conditions. The computed Na-H exchange flux (JNa-H) increased with increasing [Cl]i under both normo- and hypertonic conditions, with similar apparent Km values (~120 mM). However, the maximal
JNa-H increased by nearly 90% under hypertonic conditions. Thus, activation of Na-H exchange at low pHi requires
Cl under both normo- and hypertonic conditions, but at any given [Cl]i, JNa-H is greater under hyper- than normotonic conditions. We conclude that an increase in [Cl]i is not the primary shrinkage signal, but may act as an
auxiliary shrinkage signal. To determine whether the Cl-dependent step is after the G-protein-dependent step,
we predialyzed BMFs to a Cl-free state, and then attempted to stimulate Na-H exchange by activating a G protein.
We found that, even in the absence of Cl, dialyzing with GTP
S or AlF3, or injecting cholera toxin, stimulates Na-H
exchange. Because Na-H exchange activity was absent in control Cl-depleted fibers, the Cl-dependent step is at
or before the G protein in the shrinkage signal-transduction pathway. The stimulation by AlF3 indicates that the G
protein is a heterotrimeric G protein.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  B. Etschmann, K. S. Heipertz, A. von der Schulenburg, and M. Schweigel A vH+-ATPase is present in cultured sheep ruminal epithelial cells Am J Physiol Gastrointest Liver Physiol, December 1, 2006; 291(6): G1171 - G1179. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. G. Goss, L. Jiang, D. H. Vandorpe, D. Kieller, M. N. Chernova, M. Robertson, and S. L. Alper Role of JNK in hypertonic activation of Cl--dependent Na+/H+ exchange in Xenopus oocytes Am J Physiol Cell Physiol, December 1, 2001; 281(6): C1978 - C1990. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
O. Aharonovitz, A. Kapus, K. Szaszi, N. Coady-Osberg, T. Jancelewicz, J. Orlowski, and S. Grinstein Modulation of Na+/H+ exchange activity by Cl{-} Am J Physiol Cell Physiol, July 1, 2001; 281(1): C133 - C141. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. O. Bevensee, E. Bashi, W.-R. Schlue, G. Boyarsky, and W. F. Boron Shrinkage-induced activation of Na+/H+ exchange in rat renal mesangial cells Am J Physiol Cell Physiol, March 1, 1999; 276(3): C674 - C683. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. M. Maglova, W. E. Crowe, A. A. Altamirano, and J. M. Russell Human cytomegalovirus infection stimulates Cl-/HCO-3 exchanger activity in human fibroblasts Am J Physiol Cell Physiol, August 1, 1998; 275(2): C515 - C526. [Abstract] [Full Text] [PDF]
|
|
|
|
