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

Abstract

Osmotic cell shrinkage activates a nonselective cation (NSC) channel in M-1 mouse cortical collecting duct cells (Volk, Frömter & Korbmacher, 1995, Proc. Natl. Acad. Sci. USA 92: 8478-8482). To see whether shrinkage-activated NSC channels are an ubiquitous phenomenon, we tested the effect of hypertonic extracellular solution on whole-cell currents of HT29 human colon carcinoma cells, BSC-1 renal epithelial cells, A10 vascular smooth muscle cells, and Neuro-2a 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 microm to 12 +/- 1 microm (n = 13). Upon cell shrinkage whole-cell currents of HT29 cells increased within 8 +/- 1 min by about 30-fold (n = 13). Cell shrinkage and current activation were reversible upon return to isotonic solution. Replacement of bath Na+ by K+ or Li+ had almost no effect on the stimulated inward current. In contrast, replacement by N-methyl-d-glucamine (NMDG) completely abolished it and shifted the reversal potential from -4.5 +/- 0.7 mV to -57 +/- 4.1 mV (n = 10). Thus, the stimulated conductance is nonselective for alkali cations but highly selective for cations over anions with a cation-to-anion permeability ratio of about 13. Flufenamic acid (100 microm) inhibited the stimulated current by 84 +/- 4.7% (n = 8). During the early phase of hypertonic stimulation single-channel transitions could be detected in whole-cell current recordings, and a gradual activation of 12 and more individual channels with a single-channel conductance of 17.6 +/- 0.9 pS (n = 4) could be resolved. In analogous experiments similar shrinkage-activated NSC channels were also observed in BSC-1 renal epithelial cells, A10 vascular smooth muscle cells, and Neuro-2a neuroblastoma cells. These findings indicate that shrinkage-activated NSC channels are an ubiquitous phenomenon and may play a role in volume regulation.