Cardiac Ca current does not run down and is very sensitive to isoprenaline in the nystatin-method of whole cell recording.

The conventional L type Ca2+ channel current (ICa.L) was measured in single atrial and ventricular myocytes, with a new whole-cell recording technique using an ionophore, nystatin. The membrane of a cell-attached patch was gradually permeabilized by nystatin (100-200 micrograms/ml), added to the pipette solution, within 2-5 min after formation of a G omega-seal. The electrical activity of the cells was measured through the pipette. ICa.L, measured with the nystatin-whole cell recording technique, did not exhibit the so-called "run-down" phenomenon for up to 90 min. The response of ICa.L to isoprenaline was also well preserved during the measurement. The half maximal concentration for the isoprenaline-induced increase of ICa.L was 8.2 x 10(-9) M, which is a much smaller value than that reported previously. Thus, the nystatin-whole cell clamp recording is a useful technique to measure membrane currents of cardiac myocytes with preserving the physiological intracellular milieu.