Stimulation by caveolin-1 of the hypotonicity-induced release of taurine and ATP at basolateral, but not apical, membrane of Caco-2 cells

Abstract

germont. Stimulation by caveolin-1 of the hypotonicity-induced release of taurine and ATP at basolateral, but not apical, membrane of Caco-2 cells. Am J Physiol Cell Physiol 290: C1287-C1296, 2006. First published December 7, 2005 doi:10.1152/ajpcell.00545.2005.-Regulatory volume decrease (RVD) is a protective mechanism that allows mammalian cells to restore their volume when exposed to a hypotonic environment. A key component of RVD is the release of K ϩ , Cl Ϫ , and organic osmolytes, such as taurine, which then drives osmotic water efflux. Previous experiments have indicated that caveolin-1, a coat protein of caveolae microdomains in the plasma membrane, promotes the swelling-induced Cl Ϫ current (ICl,swell) through volume-regulated anion channels. However, it is not known whether the stimulation by caveolin-1 is restricted to the release of Cl Ϫ or whether it also affects the swelling-induced release of other components, such as organic osmolytes. To address this problem, we have studied I Cl,swell and the hypotonicity-induced release of taurine and ATP in wild-type Caco-2 cells that are caveolin-1 deficient and in stably transfected Caco-2 cells that express caveolin-1. Electrophysiological characterization of wild-type and stably transfected Caco-2 showed that caveolin-1 promoted I Cl,swell, but not cystic fibrosis transmembrane conductance regulator currents. Furthermore, caveolin-1 expression stimulated the hypotonicity-induced release of taurine and ATP in stably transfected Caco-2 cells grown as a monolayer. Interestingly, the effect of caveolin-1 was polarized because only the release at the basolateral membrane, but not at the apical membrane, was increased. It is therefore concluded that caveolin-1 facilitates the hypotonicity-induced release of Cl Ϫ , taurine, and ATP, and that in polarized epithelial cells, the effect of caveolin-1 is compartmentalized to the basolateral membrane. caveolae; osmolyte; epithelial cell; chloride channel WHEN EXPOSED TO AN ACUTE hypotonic stimulus (HTS), mammalian cells typically release K ϩ , Cl Ϫ , and organic osmolytes, such as taurine, D-myo-inositol, and sorbitol, in an attempt to counteract the volume increase and to avoid swelling-induced cell lysis (27,33,51). The cellular loss of osmolytes drives the osmotic efflux of water, thereby restoring (partially) the initial cell volume, a phenomenon also known as regulatory volume decrease (RVD). In some cell types (e.g., astrocytes, airway and intestinal epithelial cells, and pancreatic acinar cells), hypotonic swelling also provokes the release of ATP, which has been proposed to assist RVD in an autocrine/paracrine way (7,8,21,39).The ion channel that is responsible for the swelling-induced release of Cl Ϫ is known as the volume-regulated anion channel (VRAC) (also known as volume-sensitive organic osmolyteanion channel or volume-sensitive outwardly rectifying channel). VRAC is a ubiquitously expressed plasma membrane anion-selective channel that has been extensively characterized at the biophysical and pharmacolo...

Caveolae at a glance

“…Caveolae have been implicated in endocytosis, cholesterol and lipid metabolism, mechanosensation and cellular signaling. The proposed physiological roles of caveolae, however, are vastly different depending on the cell type and organ system examined (for reviews, see Parton and Simons, 2007;van Deurs et al, 2003).…”

“…In Cav1-deficient cells, release of Cl -, taurine and ATP in response to hypo-osmotic cellular swelling is defective and can be recovered by exogenous Cav1 expression (Ullrich et al, 2006). Moreover, Cav1 has been shown to be essential for mechanoactivation of protein kinase B (Akt) and for cell cycle progression under cyclic stretch in vitro and in vivo (Sedding et al, 2005).…”

Cholesterol Regulates Volume-Sensitive Osmolyte Efflux from Human SH-SY5Y Neuroblastoma Cells following Receptor Activation

“…Two major roles for cholesterol in the regulation of VSOAC have previously been proposed, i.e., that the channel is localized to lipid rafts or caveolae (Trouet et al, 1999(Trouet et al, , 2001Ullrich et al, 2006) or, alternatively, that cholesterol-induced changes in the biophysical properties of the membrane result in an altered VSOAC activity (Levitan et al, 2000;Romanenko et al, 2004;Byfield et al, 2006). In SH-SY5Y cells, depletion of cholesterol with CD, a treatment documented to disrupt lipid microdomains (Brown and London, 2000;Zidovetzki and Levitan, 2007), resulted in an enhancement of both basaland receptor-stimulated taurine efflux.…”

“…In endothelial cells, cholesterol dependence of VSOAC activity has been attributed to changes in membrane fluidity and/or a negative regulation of VSOAC by segregation of the channel into membrane lipid domains such as rafts or caveolae (Romanenko et al, 2004;Byfield et al, 2006). In contrast, in other cell types, VSOAC activity appears to be dependent upon the integrity of caveolae (Trouet et al, 1999(Trouet et al, , 2001Ullrich et al, 2006). Since multiple receptor subtypes and associated signaling proteins have been localized to caveolae and/or lipid rafts (Allen et al, 2007), it is conceivable that cholesterol availability may differentially influence swellinginduced and receptor-activated VSOAC activity.…”

The Amine-Containing Cutaneous Irritant Heptylamine Inhibits the Volume-Regulated Anion Channel and Mobilizes Intracellular Calcium in Normal Human Epidermal Keratinocytes

“…These metabolites include amino acids (e.g., glycine, glutamate, and aspartate), polyols, lactate, bicarbonate, and ATP (Grygorczyk and Guyot, 2001;Hisadome et al, 2002;Darby et al, 2003;Nilius and Droog-mans, 2003;Ullrich et al, 2006). VRACs also participate in the regulation of fundamental cell functions, particularly the regulatory volume decrease during cell swelling (Sardini et al, 2003) and the control of proliferation and apoptosis.…”