Ca 2 + -induced inactivation of L-type Ca 2 + is differentially mediated by two C-terminal motifs of the α 1 C subunit, L (1572-1587) and K (1599-1651) implicated for calmodulin binding. We found that motif L is composed of a highly selective Ca 2 + sensor and an adjacent Ca 2 + -independent tethering site for calmodulin. The Ca 2 + sensor contributes to higher Ca 2 + sensitivity of the motif L complex with calmodulin. Since only combined mutation of both sites removes Ca 2 + -dependent current decay, the two-site modulation by Ca 2 + and calmodulin may underlie Ca 2 + -induced inactivation of the channel.