Swelling-activated chloride current is persistently activated in ventricular myocytes from dogs with tachycardia-induced congestive heart failure

Abstract

The hypothesis that cellular hypertrophy in congestive heart failure (CHF) modulates mechanosensitive (ie, swelling- or stretch-activated) anion channels was tested. Digital video microscopy and amphotericin-perforated- patch voltage clamp were used to measure cell volume and ion currents in ventricular myocytes isolated from normal dogs and dogs with rapid ventricular pacing-induced CHF. In normal myocytes, osmotic swelling in 0.9T to 0.6T solution (T, relative osmolarity; isosmotic solution, 296 mOsmol/L) was required to elicit I(Cl,swell), an outwardly rectifying swelling- activated Cl- current that reversed near -33 mV and was inhibited by 1 mmol/L 9-anthracene carboxylic acid (9AC), an anion channel blocker. Block of I(Cl,swell) by 9AC simultaneously increased the volume of normal cells in hyposmotic solutions by up to 7%, but 9AC had no effect on volume in isosmotic or hyperosmotic solutions. In contrast, I(Cl,swell) was persistently activated under isosmotic conditions in CHF myocytes, and 9AC increased cell volume by 9%. Osmotic shrinkage in 1.1T to 1.5T solution inhibited both I(Cl,swell) and 9AC-induced cell swelling in CHF cells, whereas osmotic swelling only slightly increased I(Cl,swell). The current density for fully activated 9AC-sensitive I(Cl,swell) was 40% greater in CHF than normal myocytes. In both groups, 9AC-sensitive current and 9AC-induced cell swelling were proportional with changes in osmolarity and 9AC concentration, and the effects of 9AC on current and volume were blocked by replacing bath Cl- with methanesulfonate, CHF thus altered the set point and magnitude of I(Cl,swell) and resulted in its persistent activation. We previously observed analogous regulation of mechanosensitive cation channels in the same CHF model. Mechanosensitive anion and cation channels may contribute to the electrophysiological and contractile derangements in CHF and may be novel targets for therapy.