Activation of protein kinase C augments T-type Ca<SUP>2+</SUP> channel activity without changing channel surface density

초록

T-type Ca2+ channels play essential roles in numerous cellular processes. Recently, we reported that phorbol-12-myristate-13-acetate (PMA) potently enhanced the current amplitude of Ca(v)3.2 T-type channels reconstituted in Xenopus oocytes. Here, we have compared PMA modulation of the activities of Ca(v)3.1, Ca(v)3.2 and Ca(v)3.3 channels, and have investigated the underlying mechanism. PMA augmented the current amplitudes of the three T-type channel isoforms, but the fold stimulations and time courses differed. The augmentation effects were not mimicked by 4 alpha-PMA, an inactive stereoisomer of PMA, but were abolished by preincubation with protein kinase C (PKC) inhibitors, indicating that PMA augmented T-type channel currents via activation of oocyte PKC. The stimulation effect on Ca(v)3.1 channel activity by PKC was mimicked by endothelin when endothelin receptor type A was coexpressed with Ca(v)3.1 in the Xenopus oocyte system. Pharmacological studies combined with fluorescence imaging revealed that the surface density of Ca(v)3.1 T-type channels was not significantly changed by activation of PKC. The PKC effect on Ca(v)3.1 was localized to the cytoplasmic II-III loop using chimeric channels with individual cytoplasmic loops of Ca(v)3.1 replaced by those of Ca(v)2.1.

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