Genetic deletion of STAC2 adaptor protein alters electrical activity of mouse chromaffin cells.

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Voltage-gated Cav1.2 and Cav1.3 L-type Ca2+ channels (LTCCs) regulate action potential (AP) firing and catecholamine release in mouse chromaffin cells (MCCs). Src homology 3 and cysteine rich domain adaptor proteins (Stac1-Stac3) have recently been identified as novel regulators of neuronal LTCCs expression and biophysical properties. Upon overexpression in cultured hippocampal neurons Stac2 abolished LTCC Ca2+ dependent inactivation via an allosteric inhibition of calmodulin binding. Additionally, in Drosophila, deletion of the homologous DStac gene resulted in deficient LTCC Ca2+ transients and reduced neuropeptide release. Here we investigated the effect of Stac2 genetic ablation on neuronal LTCC function, electrical activity, and vesicle exocytosis in MCCs. Constitutive deletion of Stac2 does not affect the MCCs resting membrane potential or spontaneous firing frequency. However, the AP depolarization threshold was significantly reduced in Stac2-/- MCCs compared to WT (WT = −35.6 ± 1.2 mV, Stac2-/- = −40.6 ± 0.6 mV; ∗∗ P < 0.01). Additionally, step current injection elicited an electrical activity with higher initial AP firing frequency in Stac2-/- compared to WT that led to earlier depolarization block (F0 ≅2 pA current injection: WT = 0.28 ± 0.28 Hz, Stac2-/- = 0.89 ± 0.40 Hz; ∗ P < 0.05). Surprisingly, initial characterization shows that Stac2 deletion does not alter whole-cell Ca2+ current amplitude or inactivation kinetics but significantly shifts the voltage-dependence of activation to more hyperpolarized potential (V0.5: WT = −5.95 ± 1.65 mV, Stac2-/- = −15.25 ± 2.05 mV; ∗ P < 0.05). We are currently investigating possible effects of Stac2 deletion on other ionic conductances governing MCC excitability and the role on catecholamine vesicle exocytosis. Support: TWF F.18863, LFU 2021-CHEM-8 to SMG; FWF P31434, P36053, DOC30-B30 to PT; P33776 to MC.