A novel phospho-modulatory mechanism contributes to the calcium-dependent regulation of T-type Ca 2+ channels

Ca v 3 / T-type Ca 2+ channels are dynamically regulated by intracellular Ca 2+ ions, which inhibit Ca v 3 availability. Here, we demonstrate that this inhibition becomes irreversible in the presence of non-hydrolysable ATP analogs, resulting in a strong hyperpolarizing shift in the steady-state inactivation of the residual Ca v 3 current. Importantly, the effect of these ATP analogs was prevented in the presence of intracellular BAPTA. Additional findings obtained using intracellular dialysis of inorganic phosphate and alkaline phosphatase or NaN 3 treatment further support the involvement of a phosphorylation mechanism. Contrasting with Ca v 1 and Ca v 2 Ca 2+ channels, the Ca 2+ -dependent modulation of Ca v 3 channels appears to be independent of calmodulin, calcineurin and endocytic pathways. Similar findings were obtained for the native T-type Ca 2+ current recorded in rat thalamic neurons of the central medial nucleus. Overall, our data reveal a new Ca 2+ sensitive phosphorylation-dependent mechanism regulating Ca v 3 channels, with potentially important physiological implications for the multiple cell functions controlled by T-type Ca 2+ channels.