Voltage-sensitive dye RH421 increases contractility of cardiac muscle

Voltage-sensitive dyes and imaging techniques have proved to be indispensable tools for use in in vitro electrophysiological studies. To avoid motion artifacts in optical recordings, electromechanical uncouplers such as 2,3-butanedione monoxime (BDM) are required. In this study, we sought to determine whether the voltage-sensitive dye RH421 had an effect on the contractility of heart muscle, either alone or in the presence of BDM. Ventricular contractility was studied in (i) isolated rat myocytes and (ii) Langendorff-perfused rat hearts under control conditions, and during perfusion with RH421 or RH421 + BDM. The following results were obtained. (i) The amplitude of cell shortening increased progressively from 6.24 ± 0.64 to 9.95 ± 1.02 μm during 15 min of superfusion with 5 μM RH421 (n = 11), and further increased to 12.54 ± 0.97 μm during washout. In seven cells first perfused with 15 mM BDM and then with 15 mM BDM + 5 μM RH421, the amplitude of the cell shortening first decreased from 5.17 ± 0.51 to 0.41 ± 0.19 μm, then the amplitude increased to 2.63 ± 0.25 μm. (ii) Left ventricular pressure (LVP) of the heart (n = 7) was reduced by 15 mM BDM from 60.7 ± 2.5 to 2.8 ± 0.5 mmHg (1 mmHg = 133.3 Pa). LVP increased to 12.8 ± 1.1 mmHg during subsequent perfusion with 10 μM RH421 in the presence of BDM and did not change (LVP = 12.4 ± 2.4 mmHg) during washout of the dye. Therefore, RH421 increased the contractility of rat hearts and isolated myocytes with and without BDM.