Figure 3.

Pharmacological characterization of the APs and membrane potential fluctuations in spontaneously beating stage-1 and -2 cells measured under current clamp. (A) Superfusion of 140 mM K⁺ led to depolarization of the resting potential close to 0 mV and halted both APs and small membrane potential fluctuations. (B) Superfusion of the VDCC blocker nisoldipine (50 nM) interrupted the APs but not the small membrane potential fluctuations. (C) Application of the sarcoplasmic ATPase inhibitor thapsigargin (100 nM) to a stage-1 cell blocked both APs and membrane potential fluctuations and led to a depolarization of the resting potential.