Cytosolic β subunit decreases the Gβγ-mediated, voltage-dependent suppression of CaV2.2 currents. (A) N-terminal amino acid sequences of β2a, β2a(C3,4S), β2b, and β3 subunit with GFP as a fluorescent label. In the palmitoylation-resistant mutant β2a(C3,4S), both palmitoylated cysteine residues (*, blue) are replaced with serine (red). Lyn-β3 is labeled with YFP. (bottom) Confocal images of the β subunits expressed in tsA-201 cells. (B) Inhibition of CaV2.2 current by M1 receptors is significantly relieved by a prepulse (+PP) in cells with membrane-localized β subunits but not in cells with cytosolic β subunits. Cells were given a test pulse (−PP) and then depolarized to 130 mV for 20 ms, followed by the second test pulse after 20 ms (+PP). The experiments were performed before (control) and during the Oxo-M application (+Oxo-M). (bottom) Summary of the prepulse experiments in control and Oxo-M–perfused cells with different CaV β subunits. The current amplitude after Oxo-M application is given as percentage of the initial control. Data are mean ± SEM (n = 5–6). *, P < 0.01.
