HIGH-RESOLUTION MEASUREMENT AND CALIBRATION OF CA2+-TRANSIENTS USING INDO-1 IN GUINEA-PIG ATRIAL MYOCYTES UNDER VOLTAGE CLAMP

Spherical atrial myocytes obtained by enzymatic dispersion of hearts from adult guinea-pigs were loaded with the fluorescent Ca2+-indicator Indo-1 via patch-clamp pipettes. The dialysing solution additionally contained citrate (60 mM) as low-affinity ('linear') Ca2+-chelating compound in order to slow intracellular Ca2+-transients. Changes in Indo-1 fluorescence under voltage-clamp due to Ca2+-entry and/or release from the SR were calibrated using an in vivo procedure to determine the limiting fluorescence ratios. Sample recordings will be presented to demonstrate that components of a [Ca2+]i-transient due to entry via L-type Ca2+-channels and due to Ca2+-release from the SR can be directly visualized.