Optical recording of calcium currents during impulse conduction in cardiac tissue

Abstract

© The Authors. We explore the feasibility of obtaining a spatially resolved picture of Ca 2+ inward currents (I Ca ) in multicellular cardiac tissue by differentiating optically recorded Ca 2+ transients that accompany propagating action potentials. Patterned growth strands of neonatal rat ventricular cardiomyocytes were stained with the Ca 2+ indicators Fluo-4 or Fluo-4FF. Preparations were stimulated at 1 Hz, and Ca 2+ transients were recorded with high spatiotemporal resolution (50 μm, 2 kHz analog bandwidth) with a photodiode array. Signals were differentiated after appropriate digital filtering. Differentiation of Ca 2+ transients resulted in optically recorded calcium currents (ORCCs) that carried the temporal and pharmacological signatures of L-type Ca 2+ inward currents: the time to peak amounted to ~2.1 ms (Fluo-4FF) and ~2.4 ms (Fluo-4), full-width at half-maximum was ~8 ms, and ORCCs were completely suppressed by 50 μmol/L CdCl 2 . Also, and as reported before from patch-clamp studies, caffeine reversibly depressed the amplitude of ORCCs. The results demonstrate that the differentiation of Ca 2+ transients can be used to obtain a spatially resolved picture of the initial phase of I Ca in cardiac tissue and to assess relative changes of activation/fast inactivation of I Ca following pharmacological interventions.