Stretch-activated single K ⁺ channels account for whole-cell currents elicited by swelling

Abstract

Functionally significant stretch-activated ion channels have been clearly identified in excitable cells. Although single-channel studies suggest their expression in other cell types, their activity in the whole-cell configuration has not been shown. This discrepancy makes their physiological significance doubtful and suggests that their mechanical activation is artifactual. Possible roles for these molecules in nonexcitable cells are acute cell-volume regulation and, in epithelial cells, the complex adjustment of ion f luxes across individual cell membranes when the rate of transepithelial transport changes. We report the results of experiments on isolated epithelial cells expressing in the basolateral membrane stretch-activated K ؉ channels demonstrable by the cell-attached patch-clamp technique. In these cells, reversible whole-cell currents were elicited by both isosmotic and hyposmotic cell swelling. Cation selectivity and block by inorganic agents were the same for single-channel and whole-cell currents, indicating that the same entity underlies singlechannel and whole-cell currents and that the single-channel events are not artifactual. In these cells, when the rate of apical-membrane NaCl entry increases, the cell Na ؉ content and volume also increase, stimulating the Na ؉ ,K ؉ -ATPase at the basolateral membrane, i.e., both Na ؉ extrusion and K ؉ uptake increase. We speculate that, under these conditions, the parallel activation of basolateral K ؉ channels (by the swelling) elevates conductive K ؉ loss, tending to maintain the cell K ؉ content constant (''pump-leak parallelism''). This study describes a physiologically relevant stretch-activated channel, at both the single-channel and whole-cell levels, in a nonneural cell type.

A mechanogated nonselective cation channel in proximal tubule that is ATP sensitive

“…Indeed, only within the past 2 yr have data been presented to support the hypothesis that epithelial SA channels in cell-attached patches underlie the whole cell currents elicited by cellular swelling (44). One mechanism that may be involved in the RVD of epithelial cells exposed to hypotonicity involves Ca 2ϩ entry via SA-NSC channels, which in turn activates Ca 2ϩ -activated K ϩ channels in the same membrane (5).…”

“…For this reason, the SA-NSC channel described may play a role during transepithelial transport under healthy conditions. In this case, the SA-NSC channel could become active in response to both cellular swelling (44) and reductions in [ATP] i , allowing Na ϩ or Ca 2ϩ to enter or (less likely) K ϩ to exit. We have previously shown that intracellular Ca 2ϩ is an important regulator of the hyperpolarization-activated K ATP channel in the same membrane (22).…”

Physiology of Cell Volume Regulation in Vertebrates

“…Membrane stretch is not a universal mechanism of activation of I K,vol , since, e.g., in EAT cells, this channel cannot be activated directly by membrane stretch (134). However, several K ϩ channels, including some BK channels (272), and some K 2P channels (379, 542, 610, 611, 774) are activated both directly by membrane stretch and by cell swelling, and it seems that in some cases, stretch-activated K ϩ channels can account for I K,vol (1028). B) CYTOSKELETON.…”

The Mechanosensitive Ca2+ Channel as a Central Regular of Prostate Tumor Cell Migration and Invasiveness

“…However, osmotic cell swelling also activates a number of membrane-associated enzymes, including Src kinase and phospholipase A2 (PLA 2 ) (Lehtonen and Kinnunen 1995;Cohen 2005a). Furthermore, although some stretch-sensitive channels are sensitive to osmotic cell swelling and direct cell inflation, others are not (Levina et al 1999;Vanoye and Reuss 1999;Hamill 2000a, 2000b). One basis for this difference is that some cells may possess large excess membrane reserves in the form of folds microvilli and caveola (e.g., Xenopus oocytes and skeletal muscle) that can buffer rapid increases in bilayer tension Hamill 2000a, 2000b;.…”

“…Osmotic stress can also be used to test if a channel is MS either by swelling the cell while recording from a cell-attached patch or from the whole cell (Hamill 1983;Christensen 1987;Sackin 1989;Cemerikic and Sackin 1993;Vanoye and Reuss 1999;Numata et al 2007). The advantage of this approach is that the action of inhibitors and activators can be consistently recognized when assessed on whole cell vs patch currents.…”