OPTICAL MULTISITE MONITORING OF CELL EXCITATION PHENOMENA IN ISOLATEDCARDIOMYOCYTES

An especially designed setup which consists of an inverted fluorescenc e microscope, an argon ion laser and a photodiode array system permits membrane potential monitoring in isolated guinea-pig ventricular card iomyocytes, stained with the voltage-sensitive dye di-4-ANEPPS, which responds linearly with relative fluorescence changes (Delta F/F)approx imate to-8% per 100 mV. About a dozen measuring spots covering a singl e cell were simultaneously monitored with a spatial and temporal resol ution of 15 mu m and about 20 mu s, respectively. In general, the risi ng phases of the action potentials within a single cell were highly sy nchronized (i.e. all upstroke velocities peaked within about 20 mu s); however, in one cell (out of 25 examined) significant (P < 0.05) time lags exceeding the signal-dependent time resolution were also found. Experiments, simultaneously performed with our optical system and a wi dely used patch-clamp setup, revealed a slowed and delayed response of the clamp amplifier depending on the cell access resistance. Optical monitoring during whole-cell voltage-clamping demonstrated the influen ce of graduated series resistance compensation. When held stimulation was used, our results clearly demonstrated the spatially dependent pol arization of the cell membrane during the stimulus, as well as a highl y synchronized upstroke development. Slight differences in the maximum upstroke velocities within a single cell were also found and were bas ically in agreement with mathematical models.