Characterization of isolated ventricular myocytes: two levels of resting potential

Standard microelectrode and whole cell patch clamp techniques were used to characterize the resting properties of ventricular myocytes obtained by enzymatic dispersion from rabbit hearts. In 37 cells studied under current clamp using intracellular microelectrodes, three distinct group of cells can be recognized. The first group (23 cells) is constituted by permanently depolarized cells (RP = -24 +/- 5 mV; Rm = 8.1 +/- 3.4 K omega cm2; Cm = 2.4 +/- 1.2 microF/cm2). A second group (13 cells) is constituted by cells able to be in two distinct states: D state (RP = -28 +/- 11 mV; Rm = 15.2 +/- 9.1 k omega cm2; Cm = 3.8 +/- 0.8 microF/cm2) and H state (RP = -74 +/- 8 mV; Rm = 3.2 +/- 2.3 K omega cm2 and Cm = 2.9 +/- 2.3 microF/cm2). Some of these cells were able to switch between the two states. The third group is represented by one cell and had only one resting potential in the H state range. Resting potential of permanently depolarized cells and cells in D state did not depend on extracellular potassium concentration. In H state however, it varied with extracellular potassium for concentrations above 2.5 mM as expected for a potassium electrode; for lower concentrations a strong deviation was observed. Accordingly, the steady state current voltage plot obtained under whole cell voltage clamp conditions showed either one zero current potential with positive slope conductance at the D state resting range; two zero current voltages corresponding to D and H state resting levels or only one zero current potential at H state resting level.(ABSTRACT TRUNCATED AT 250 WORDS)