Regulation of cell-volume and cytoplasmic content of solutes by CFTR Cl Channel in cardiac cells

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1. Role of CFTR Cl current in volume regulation in cardiac cellsThe effects of activation of cyclic AMP-dependent Cl^- current (I_<Cl, cAMP>) on cell volume were studied at various [K^+]_O under isosmotic conditions in guinea-pig ventricular myocytes. The area of the cell image obtained with videomicroscopy was used as an index of cell volume. I_<Cl, cAMP> was activated by adrenaline (5.5 μM). At 5.4 mM [K^+]_O with low [Cl^-]_O, where V_m was negative to the predicted equilibrium potential of Cl^- (E_<Cl>), adrenaline decreased the cell area sizably. At high [K^+]_O with normal [Cl^-]_O, where V_m was positive to E_<Cl>, adrenaline increased the cell area ; at 145.4 mM [K^+]_O the cell area was increased to about 110% of control. Addition of BaCl_2 (1mM), a blocker of K^+ channels, attenuated the adrenaline-dependent cell swelling, supporting the view that Cl^- fluxes must be accompanied by co-fluxes of K^+ ions, to affect the cell volume. The results show that activation of I_<Cl, cA … More MP> can shrink or inflate the cardiac cells under isosmotic conditions, depending on V_m and E_<Cl>2. Role of Na-K-2Cl and K-Cl cotransporters in volume regulation in cardiac cellsApplication of Na-deficient or Cl-deficient solution to the cell induced a decrease in cell volume. A similar cell-shrinkage was induced also by application of bumetanide (10μM) or furosemide (2mM), and in the presence of these diuretics, Na-removal was without effect on cell volume. These results are consistent with the view that Na-K-2Cl cotransporter (NKCC), that is sensitive to the diuretics, plays a role in cell-volume regulation in cardiac cells. However, Cl-removal in the presence of bumetanide (10μM) induced a cell shrinkage. This bumetanide-insensitive, Cl-dependent cell shrinkage was found to be K-dependent, Na-independent, and furosemide-sensitive. These findings can be explained by assuming that K-Cl cotransporter (KCC) activates in low-Cl or low-K solution, thereby affecting the cell volume, that 10μM bumetanide does not inhibit KCC, and that 2 mM furosemide does inhibit it. Our results show that both NKCC and KCC play a role in cell-volume regulation in cardiac cells. Less