Fig. 6. Regulation of N-type channel activity by individual CSP regions. (A) Current records obtained with N-type (_1B + ₂ - + ß_1b) calcium channels expressed in tsa-201 cells before and after application of a 50 millisecond prepulse (pp) to +150 mV. Currents were elicited by stepping from a holding potential of -100 mV to a test potential of +20 mV. In the absence of CSP (left traces), the prepulses do not affect peak current amplitude. Following coexpression of either the cysteine string domain (middle traces) or the J domain (right traces), the channels undergo a tonic G protein inhibition that is reversed by the prepulses. In all traces, the vertical and horizontal bars indicate, respectively, a current amplitude of 200 pA and a 20 milliseond duration. (B) Bar graph illustrating the degree of prepulse relief in the absence and presence of CSP fragments. Additional coexpression of the C-terminal fragment (residues 495-689) of the ß-adrenergic receptor kinase (ßARK) reduces the CSP-mediated current inhibition as shown by the reduced PP relief. The numbers in parentheses reflect the number of experiments; the asterisks indicate statistical significance relative to control conditions at P<0.05 level.