Pharmacological Dissection of the Crosstalk between Na V and Ca V Channels in GH3b6 Cells.

Thanks to the crosstalk between Na ⁺ and Ca ²⁺ channels, Na ⁺ and Ca ²⁺ homeostasis interplay in so-called excitable cells enables the generation of action potential in response to electrical stimulation. Here, we investigated the impact of persistent activation of voltage-gated Na ⁺ (Na _V ) channels by neurotoxins, such as veratridine (VTD), on intracellular Ca ²⁺ concentration ([Ca ²⁺ ] _i ) in a model of excitable cells, the rat pituitary GH3b6 cells, in order to identify the molecular actors involved in Na ⁺ -Ca ²⁺ homeostasis crosstalk. By combining RT-qPCR, immunoblotting, immunocytochemistry, and patch-clamp techniques, we showed that GH3b6 cells predominantly express the Na _V 1.3 channel subtype, which likely endorses their voltage-activated Na ⁺ currents. Notably, these Na ⁺ currents were blocked by ICA-121431 and activated by the β-scorpion toxin Tf2, two selective Na _V 1.3 channel ligands. Using Fura-2, we showed that VTD induced a [Ca ²⁺ ] _i increase. This effect was suppressed by the selective Na _V channel blocker tetrodotoxin, as well by the selective L-type Ca _V channel (LTCC) blocker nifedipine. We also evidenced that crobenetine, a Na _V channel blocker, abolished VTD-induced [Ca ²⁺ ] _i elevation, while it had no effects on LTCC. Altogether, our findings highlight a crosstalk between Na _V and LTCC in GH3b6 cells, providing a new insight into the mode of action of neurotoxins.