Low osmolarity transforms ventricular fibrillation from complex to highly organized, with a dominant high-frequency source

BACKGROUND An osmotic challenge activates volume-regulated chloride currents resulting in depolarization of the resting membrane potential and shortening of action potential duration (APD). I-Cl,I-vol is activated in ischemia/reperfusion, but the effects of osmotic challenges and I-Cl,I-vol on ventricular fibrillation (VF) are unknown. OBJECTIVES The purpose of this study was to investigate the influence of hypo-osmotic and hypotonic stress and I-Cl,I-vol activation on VF dynamics. METHODS Guinea pig hearts were isolated, stained with di-4 ANEPPS to optically map action potentials (APs) from epicardium using a photodiode array, and perfused with iso-osmotic (tow NaCl Ringer plus 45 mM mannitol) or hypo-osmotic (tow NaCl Ringer) solution. RESULTS Hypo-osmotic solution shortened APDs (143 +/- 5 ms --> 115 +/- 10 ms) and increased APD gradients between right and left ventricles (21 +/- 7 ms --> 41 +/- 10 ms, n = 4). In VF induced by burst stimulation, switching to hypo-osmotic solution increased VF frequencies (15.3 +/- 1.2 Hz to 28.9 +/- 3.6 Hz, n = 11), transforming complex fast Fourier transformation spectra to a single dominant high frequency on the left but not the right ventricle. Perfusion with the I-Cl,I-vol blocker indanyloxyacetic acid-94 (10 mu M) reversed organized VF to complex VF with Lower (13.5 +/- 3.7 Hz in left ventricle) frequencies (n = 8), indicating that I-Cl,I-vol underlies the changes in VF dynamics. Consistent with this interpretation, the levels of ClC-3 channel protein were 27% greater on left than right ventricles (n = 10), and computer simulations showed that insertion of I-Cl,I-vol transformed complex VF to a stable spiral. CONCLUSION Activation of I-Cl,I-vol by decreasing osmolarity (45 mOsm) has a major impact on VF dynamics by transforming random multiple wavelets to a highly organized VF with a single dominant frequency.