C-terminal fragments of the alpha(1C) (Ca(v)1.2) subunit associate with and regulate L-type calcium channels containing C-terminal-truncated alpha(1C) subunits

L-type Ca2+ channels in native tissues have been found to contain a pore-fo rming alpha (1) subunit that is often truncated at the C terminus. However, the C terminus contains many important domains that regulate channel funct ion. To test the hypothesis that C-terminal fragments may associate with an d regulate C-terminal-truncated alpha (1C) (Ca(V)1.2) subunits, we performe d electrophysiological and biochemical experiment, In tsA201 cells expressi ng either wild type or C-terminal-truncated alpha (1C) subunits in combinat ion with a beta (2a) subunit, truncation of the alpha (1C) subunit by as li ttle as 147 amino acids led to a 10-15-fold increase in currents compared w ith those obtained from control, full-length alpha (1C) subunits, Dialysis of cells expressing the truncated alpha (1C) subunits with C-terminal fragm ents applied through the patch pipette reconstituted the inhibition of the channels seen with full-length alpha (1C) Subunits. In addition, C-terminal deletion mutants containing a tethered C terminus also exhibited the C-ter minal-induced inhibition. Immunoprecipitation assays demonstrated the assoc iation of the C-terminal fragments with truncated alpha (1C) subunits, In a ddition, glutathione S-transferase pull-down assays demonstrated that the C -terminal inhibitory fragment could associate with at least two domains wit hin the C terminus. The results support the hypothesis the C-terminal fragm ents of the alpha (1C) subunit can associate with C-terminal-truncated alph a (1C) subunits and inhibit the currents through L-type Ca2+ channels.