Molecular nature of anomalous L-type calcium channels in mouse cerebellar granule cells

Single-channel analysis revealed the existence of neuronal L-type Ca2+ channels (LTCCs) with fundamentally different gating properties; in addition to LTCCs resembling cardiac channels, LTCCs with anomalous gating were identified in a variety of neurons, including cerebellar granule cells. Anomalous LTCC gating is mainly characterized by long reopenings after repolarization following strong depolarizations or trains of action potentials. To elucidate the unknown molecular nature of anomalous LTCCs, we performed single-channel patch-clamp recordings from cerebellar granule cells of wild-type, Ca(v)1.3-/- and Ca(v)1.2DHP-/- [containing a mutation in the Ca(v)1.2 alpha1 subunit that eliminates dihydropyridine (DHP) sensitivity] mice. Quantitative reverse transcription-PCR revealed that Ca(v)1.2 accounts for 89% and Ca(v)1.3 for 11% of the LTCC transcripts in wild-type cerebellar granule cells, whereas Ca(v)1.1 and Ca(v)1.4 are expressed at insignificant levels. Anomalous LTCCs were observed in neurons of Ca(v)1.3-/- mice with a frequency not different from wild type. In the presence of the DHP agonist (+)-(S)-202-791, the typical prepulse-induced reopenings of anomalous LTCCs after repolarization were shorter in Ca(v)1.2DHP-/- neurons than in Ca(v)1.3-/- neurons. Reopenings in Ca(v)1.2DHP-/- neurons in the presence of the DHP agonist were similar to those in wild-type neurons in the absence of the agonist. These data show that Ca(v)1.2alpha1 subunits are the pore-forming subunits of anomalous LTCCs in mouse cerebellar granule cells. Given the evidence that Ca(v)1.2 channels are specifically involved in sustained Ras-MAPK (mitogen-activated protein kinase)-dependent cAMP response element-binding protein phosphorylation and LTCC-dependent hippocampal long-term potentiation (LTP) (Moosmang et al., 2005), we discuss the hypothesis that anomalous rather than cardiac-type Ca(v)1.2 channels are specifically involved in LTCC-dependent and gene transcription-dependent LTP.