Fig. 4.
Mutation A454T prevents P/Q channel regulation by MPC endogenous syntaxin 1A. (A) Inhibition of WT P/Q channels alone (Left, control) or coexpressed with BTX C (Right) in mouse pheochromocytoma (MPC 9/3L-AH) cells, evaluated as described in Fig. 3. (B) Average percentage ICa inhibition for WT P/Q channels expressed alone (control) or with BTX C in MPC 9/3L-AH cells. Ca2+ currents were normalized to the current following the −80-mV prepulse. *P < 0.01. (C) Average current evoked by every 10th pulse of a 200-Hz train of 2-ms depolarizations from −80 mV to +20 mV, normalized to the current evoked by the first pulse of the train, obtained from MPC 9/3L-AH cells expressing WT or A454T P/Q channels alone or coexpressed with BTX C, as indicated. (D) Western blot of cell lysates obtained from HEK 293 cells expressing syntaxin 1A alone or with botulinum toxin C (BTX C) and probed with anti-syntaxin 1A and α-tubulin antibodies. Full-length and cleaved syntaxin 1A are detected in the presence of BTX C. Methodological details can be found in SI Methods.