Osmotic shrinkage activates nonselective cation (NSC) channels in various cell types

Osmotic cell shrinkage activates a nonselective cation (NSC) channel in M-l mouse cortical collecting duct cells (Volk, Fromter & Korbmacher, 1995, Pr oc. Natl. Acad. Sci. USA 92: 8478-8482). To see whether shrinkage-activated NSC channels are an ubiquitous phenomenon, we tested the effect of hyperto nic extracellular solution on whole-cell currents of HT29 human colon carci noma cells, BSC-1 renal epithelial cells, A10 vascular smooth muscle cells, and Neuro-a neuroblastoma cells. Addition of 100 mM sucrose to an isotonic NaCl bath solution induced cell shrinkage of HT29 cells as evidenced by a decrease in cell diameter from 18 +/- 1 mu m to 12 +/- 1 mu m (n = 13). Upo n cell shrinkage whole-eel currents of HT29 cells increased within 8 +/- 1 min by about 30-fold(n = 13). Cell shrinkage and current activation were re versible upon return to isotonic solution. Replacement of bath Na+ by K+ or Li+ had almost no effect on the stimulated inward current. In contrast, re placement by N-methyl-D-glucamine (NMDG) completely abolished it and shifte d the reversal potential from -4.5 +/- 0.7 mV to -57 +/- 4.1 mV (12 = 10). Thus, the stimulated conductance is nonselective for alkali cations bur hig hly selective for cations over anions with a cation-to-anion permeability r atio of about 13. Flufenamic acid (100 mu M) inhibited the stimulated curre nt by 84 +/- 4.7% (n = 8). During the early phase of hypertonic stimulation single-channel transitions could be detected in whole-cell current recordi ngs, and a gradual activation of 12 and more individual channels with a sin gle-channel conductance of 17.6 +/- 0.9 pS (Iz = 4) could be resolved. In a nalogous experiments similar shrinkage-activated NSC channels were also obs erved in BSC-1 renal epithelial cells, A10 vascular smooth muscle cells, an d Neuro-2a neuroblastoma cells. These findings indicate that shrinkage-acti vated NSC channels are an ubiquitous phenomenon and may play a role in volu me regulation.