Modulation of CaV2.1 channels by the neuronal calcium-binding protein visinin-like protein-2

Ca(V)2.1 channels conduct P/Q- type Ca2+ currents that are modulated by calmodulin ( CaM) and the structurally related Ca2+- binding protein 1 ( CaBP1). Visinin- like protein- 2 ( VILIP- 2) is a CaM- related Ca2+- binding protein expressed in the neocortex and hippocampus. Coexpression of Ca(V)2.1 and VILIP- 2 in tsA- 201 cells resulted in Ca2+ channel modulation distinct from CaM and CaBP1. Ca(V)2.1 channels with beta(2a) subunits undergo Ca2+- dependent facilitation and inactivation attributable to association of endogenous Ca2+/CaM. VILIP- 2 coexpression does not alter facilitation measured in paired- pulse experiments but slows the rate of inactivation to that seen without Ca2+/ CaM binding and reduces inactivation of Ca2+ currents during trains of repetitive depolarizations. Ca(V)2.1 channels with beta 1b subunits have rapid voltage- dependent inactivation, and VILIP- 2 has no effect on the rate of inactivation or facilitation of the Ca2+ current. In contrast, when Ba2+ replaces Ca2+ as the charge carrier, VILIP- 2 slows inactivation. The effects of VILIP- 2 are prevented by deletion of the CaM- binding domain ( CBD) in the C terminus of Ca(V)2.1 channels. However, both the CBD and an upstream IQ- like domain must be deleted to prevent VILIP- 2 binding. Our results indicate that VILIP- 2 binds to the CBD and IQ- like domains of Ca(V)2.1 channels like CaM but slows inactivation, which enhances facilitation of Ca(V)2.1 channels during extended trains of stimuli. Comparison of VILIP- 2 effects with those of CaBP1 indicates striking differences in modulation of both facilitation and inactivation. Differential regulation of Ca(V)2.1 channels by CaM, VILIP- 2, CaBP1, and other neurospecific Ca2+- binding proteins is a potentially important determinant of Ca2+ entry in neurotransmission.