A study on the role of two different Ca^<2+> channel families in neurons

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(1) We have isolated two cDNAs encoding RNA splicing variants of human Ca^<2+> channel a1B subunit from human brain cDNA libralies. These variants were proved to be the RNA splicing variants by genomic analysis. One of the variants lacking the II-III linker region formed Ca^<2+>-permeable channel having low ω-conotoxin sensitivity, as revealed by exogenous expression in human embryonic kidney (HEK) cells. (2) We have analyzed the G-protein-mediated modulation of P/Q-type, α_<1A> channels biochemically and electrophygiologically, and found that the interaction of N-terminal region of Gα_o and C-terminal domain of a_<1A> subunit causes the voltage-resistant inhibition of P/Q-type channel current. (3) We have found, using Xenopus oocyte expression system, that cytosolic Ca^<2+> is required for the opening of store-operated TRP4 channels, and that the activation of inositol-1, 4, 5-trisphosphate receptor (IP_3-R) is required and sufficient for the opening of receptor-activated TRP5 channels. (4) We have found the store-operated and receptor-activated Ca^<2+> entry in rat cerebral cortical neurons in culture by Fura-2 fluorometry. By RT-PCR analysis, we found the presence of rat TRP1, 3, 5 and 6 mRNAs in neurons. Immunostaninig results also suggest that TRP1 and 5 proteins are expressed in the cultured neurons.