External anions and volume-sensitive anion current in guinea-pig ventricular myocytes

The objective of this study was to determine the effects of anion replacement on volume-sensitive anion current in guinea-pig ventricular myocytes. Myocytes in the conventional whole-cell voltage-clamp configuration were superfused and dialysed with Na⁺-, K⁺-, and Ca²⁺-free solution, and exposed to external 75 mM Cl^- solution of one-half normal osmolality. Prolonged exposures to hyposmotic solution promoted the development of outwardly-rectifying currents that were inactivated at high positive potentials and reversed in a Cl^--dependent manner (50 mV per decade pipette Cl^- concentration). Replacement of external Cl^- by iodide and aspartate affected the reversal potential (E(rev)) and slope conductance of the volume-sensitive current. Relative permeabilities calculated from changes in E(rev) were 1.49 ± 0.09, 1.00, and 0.29 ± 0.04 for iodide, Cl^-, and aspartate, respectively; relative slope conductances between E(rev) and E(rev) + 40 mV were 1.21 ± 0.09, 1.00, and 0.43 ± 0.07, respectively. Replacement of Cl^- also affected the time dependence of the volume-sensitive current; replacement by iodide reversibly enhanced the decay of outward current at positive potentials, whereas replacement by aspartate reduced it. These results are compared with earlier findings on noncardiac time- and voltage-dependent anion current activated by hyposmotic solution.