Two-dimensional millisecond analysis of intracellular Ca2+ sparks in cardiac myocytes by rapid scanning confocal microscopy: increase in amplitude by isoproterenol.

Two dimensional images of myocardial Ca2+ sparks, non-propagating local rises in cytoplasmic Ca2+ concentration, were obtained at 4 msec intervals with a rapid-scanning confocal laser microscope, Nikon RCM 8000, and fluo-3. Spontaneous Ca2+ sparks were observed at apparently random sites throughout the cytoplasm of rat ventricular cells. The duration of sparks was 30 to 40 msec and the time to peak intensity about 10 msec. Ryanodine (1 microM) completely inhibited Ca2+ sparks while nicardipine (3 microM) had no effect. Isoproterenol (1 microM) had no effect on the frequency and distribution of Ca2+ sparks but significantly increased their amplitude. These results suggest that myocardial Ca2+ sparks are the result of spontaneous release of Ca2+ from the sarcoplasmic reticulum and that beta-adrenergic stimulation may result in functional modification of the ryanodine receptor channel.