EFFECTS OF SPONTANEOUS MYOCARDIAL OSCILLATION ON CARDIAC-FUNCTION - DIRECT OBSERVATION OF THE EPICARDIAL FLUORESCENCE IMAGE IN CALCIUM OVERLOADED ISOLATED HAMSTER HEARTS

Objectives: Calcium overload induces spontaneous cyclic calcium releas e from the sarcoplasmic reticulum, leading to spontaneous myocardial o scillation. This study was designed to elucidate (1) the effect of the myocardial oscillation on changes in ventricular performance and (2) how these changes relate to the strength of the diastolic spontaneous myocardial oscillation and the spatial extent-that is, in how extensiv e an area of the epicardium it occurred. Methods: the isovolumic press ure of the left ventricle and epicardial fura 2 fluorescence in isolat ed hamster hearts were simultaneously observed at various calcium conc entrations ([Ca2+](o)). Endothelial cells and pericytes of the capilla ries, preferentially stained by fura 2, were passively oscillated by s urrounding myocytes during diastole at concentrations greater than 1 m mol/l of [Ca2+](o). The strength of the myocardial oscillation was eva luated as the root mean square (RMS) of fluctuation in the distance be tween endothelial cells or pericytes, The spatial extent of the myocar dial oscillation was estimated as the appearance rate, defined as the ratio of the number of microscopic fields showing the capillary oscill ation, to the total number of examined fields. Results: Up to 4 mmol/l of [Ca2+](o), developed pressure and maximum rate of pressure rise si gnificantly increased in a manner dependent on [Ca2+](o), but a furthe r increase in [Ca2+](o) significantly decreased these parameters. In t he presence of ryanodine (2.5 mu mol/l), developed pressure and maximu m rate of pressure rise monotonously increased in a manner dependent o n [Ca2+](o). Although the oscillation was never observed at 1 mmol/l o f [Ca2+](o) (appearance rate = 0%), it occurred in some of the microsc opic fields at 2 and 4 mmol/l (appearance rate = 19.5 and 56.3%, respe ctively) and occurred in all microscopic fields at concentrations grea ter than 4 mmol/l (appearance rate = 100%). Ryanodine, which completel y eliminated the capillary oscillation, inhibited the increase of both RMS and end-diastolic pressure by an increase in [Ca2+](o). Conclusio ns: Our data suggest that the myocardial oscillation impairs systolic and diastolic function in intact ventricle, and that these effects are associated with the spatial extent and the strength of the myocardial oscillation.