Block of skeletal L-type current by nifedipine. (A) Incomplete block of L-type current by 1 μM nifedipine. (B) Incomplete block of L-type current by 10 μM nifedipine. (C) Complete block of L-type current by 50 μM nifedipine. Currents evoked by step depolarizations to +30 mV from −50 mV after a prepulse protocol (see Materials and methods). (D) Dose–response relationship for the effects of nifedipine, which were measured ∼1 min after addition. Note that the minimal apparent block (at 1 nM) was ∼80%, most likely as a consequence of current rundown. Each symbol represents data collected from 2–10 cells.