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 (I(Cl,vol)), resulting in depolarization of the resting membrane potential and shortening of action potential duration (APD). I(Cl,vol) is activated in ischemia/reperfusion, but the effects of osmotic challenges and I(Cl,vol) on ventricular fibrillation (VF) are unknown.


OBJECTIVE
The purpose of this study was to investigate the influence of hypo-osmotic and hypotonic stress and I(Cl,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 (low NaCl Ringer plus 45 mM mannitol) or hypo-osmotic (low 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,vol) blocker indanyloxyacetic acid-94 (10 muM) reversed organized VF to complex VF with lower (13.5 +/- 3.7 Hz in left ventricle) frequencies (n = 8), indicating that I(Cl,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,vol) transformed complex VF to a stable spiral.


CONCLUSIONS
Activation of I(Cl,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.
Choi
Bum-Rak
BR
Department of Biomedical Engineering, Tulane University, New Orleans, Louisiana, USA.
Hatton
William J
WJ
Hume
Joseph R
JR
Liu
Tong
T
Salama
Guy
G
D000818:Animals; D003198:Computer Simulation; D004195:Disease Models, Animal; D004234:Diuretics, Osmotic / Q000494:pharmacology*; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007552:Isotonic Solutions / Q000494:pharmacology; D008297:Male; D008353:Mannitol / Q000494:pharmacology*; D009994:Osmolar Concentration; D010477:Perfusion; D000077331:Ringer's Solution; D014693:Ventricular Fibrillation / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D016276:Ventricular Function / Q000187:drug effects
D004234:Diuretics, Osmotic; D007552:Isotonic Solutions; D008353:Mannitol; D000077331:Ringer's Solution