CARDIAC L-TYPE CA2+ CHANNEL TRIGGERS TRANSMITTER RELEASE IN PC12 CELLS

Among the various voltage-sensitive Ca2+ channels present in PC12 cells are the dihydropyridine (DHP)-sensitive L-channel, the omega-conotoxin (omega-CgTx)-sensitive N-channel, and an atypical omega-CgTx/DHP-insensitive Ca2+ channel. Depolarization-evoked Ca2+ entry and [H-3]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-specitic 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 alpha 1 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.