Fig. 2.
Effects of β4a and β4bon the blockade of Cav2.1 channels by ω-CTx-MVIIC. Studies were performed with Xenopus oocytes expressing α1A, α2/δ-1, and either β4a or β4b.A, Onset and degree of block by a 10 min exposure to 2 μmω-CTx-MVIIC for Cav2.1 subunit combinations at a holding potential (HP) of −80 mV. Each pointrepresents the mean of seven (β4a) or eight (β4b) different recordings. The SEM is shown for each data point unless smaller than thesymbol. Onset of block for both subunit combinations was fit (line) to a single-exponential time course plus a constant. B, The rate constants for the time course of the onset of toxin block were determined from steady-state degree of block from single exponential fits at four different toxin concentrations (0.2, 0.6, 2, and 6 μm) for Cav2.1 complexes containing either β4a or β4b. The averaged rate constants were plotted as a function of toxin concentration (minimum of n = 7, ±SEM). The line represents a linear fit to the data.