Effect of 1 μM Mb1a and Mb1b on P. americana HVA CaV channel currents. (a) M-LVA IBa were elicited by 100-ms depolarizing test pulses to +20 mV from a holding potential of −90 mV. (b,c) Representative superimposed HVA IBa showing tonic block of HVA CaV channel currents before (black lines) and following a 3 min perfusion (red lines) with (b) 1 µM Mb1a and (c) 1 µM Mb1b. Dashed gray lines represent zero current. (d,e) Timecourse of inhibition of normalized peak HVA CaV channel currents by (d) 1 µM Mb1a and (e) 1 µM Mb1b. Data are mean ± S.E.M, n = 4. Average normalized peak IBa before (open circles), during (red circles), and after (blue circles) perfusion with 1 μM toxin. Data are mean ± S.E.M of 5 experiments (panel d) or 3 experiments (panel e). Inhibition of IBa by Mb1a was significantly greater than for Mb1b (p = 0.007).