Cardiac L-type Ca²⁺ channel triggers transmitter release in PC 12 cells

Among the various voltage-sensitive Ca²⁺ channels present in PC 12 cells are the dihydropyridine (DHP)-sensitive L-channel, the ω-conotoxin (ω-CgTx)-sensitive N-channel, and an atypical ω-CgTx/DHP-insensitive Ca²⁺ channel. Depolarization-evoked Ca²⁺ entry and [³H]dopamine release is mediated by L-type Ca²⁺ channels determined by the use of Ca²⁺ channel antagonists, and a single protein of 250 kDa is recognized by L-type-specific antibodies. Screening of a PC12 cDNA library revealed two types of Ca²⁺channels which were identified by partial sequencing. A pc12-L clone displayed virtually identical sequence homology to the cardiac L-type channel. The identical sequence homology of the single alternative splicing region confirmed clone pc12-L as the rbC-I transcript, a cardiac-neuronal α1 subunit expressed in rat brain. Clone pc12-N displayed identical sequence homology to rbB-I, a neuronal al subunit of the N-type Ca²⁺ channel expressed in rat brain; Northern blot analysis identified RNA of a size similar to that previously described for rat brain.