The skeletal muscle L-type channel conducts Mn²⁺. (A) I-V relationship for normal myotubes in 10 mM of external Mn²⁺ (○; n = 4) for currents elicited at 0.1 Hz by test potentials ranging from −20 through +80 mV in 10-mV increments after a prepulse protocol. The smooth curves are plotted according to Eq. 1. The best-fit parameters for each plot are presented in Table I. (B) Representative currents recorded at +30 mV from a normal myotube in 10 mM Ca²⁺ (bottom trace), in 10 mM Mn²⁺ (middle trace), and in 10 mM Mn²⁺ after acute application of 10 μM nifedipine (top trace). (C) L-type current evoked by steps from −50 to 0 mV (top) and to +30 mV (bottom) in 0.5 mM Mn²⁺. (D) Average peak currents in 10 mM of divalent cation at a test potential of +30 mV (left) and for 0.5 mM Mn²⁺ at the indicated test potentials (right).