*+ Among the various voltage-sensitive Ca charmels present in PC12 cells are the dihy~op~idine (DHP)-sensitive L-channel, the w-conotoxin (w-CgTx)-sensitive N-channel, and an atypical w-CgTx/DHP-insensitive Ca*+ channel. Depolarization-evoked Ca*' entry and [3H]dopamine release is mediated by L-type Ca*' channels determined by the use of Ca*' 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 Ca*' channels which were identified by partial sequencing. A pcl2-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 pcl2-L as the rbC-I transcript, a cardiac-neuronal al subunit expressed in rat brain. Clone pcl2-N displayed identical sequence homology to rbB-I, a neuronal al subunit of the N-type Ca '+ channel expressed in rat brain; Northern blot analysis identified RNA of a size similar to that previously described for rat brain.

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