Deletion of the αδ-1 calcium channel subunit increases excitability of mouse chromaffin cells.

High voltage-gated Ca channels (HVCCs) shape the electrical activity and control hormone release in most endocrine cells. HVCCs are multi-subunit protein complexes formed by the pore-forming α and the auxiliary β, αδ and γ subunits. Four genes code for the αδ isoforms. At the mRNA level, mouse chromaffin cells (MCCs) express predominantly the CACNA2D1 gene coding for the αδ-1 isoform. Here we show that αδ-1 deletion led to ∼60% reduced HVCC Ca influx with slower inactivation kinetics. Pharmacological dissection showed that HVCC composition remained similar in αδ-1 MCCs compared to wild-type (WT), demonstrating that αδ-1 exerts similar functional effects on all HVCC isoforms. Consistent with reduced HVCC Ca influx, αδ-1 MCCs showed reduced spontaneous electrical activity with action potentials (APs) having a shorter half-maximal duration caused by faster rising and decay slopes. However, the induced electrical activity showed opposite effects with αδ-1 MCCs displaying significantly higher AP frequency in the tonic firing mode as well as an increase in the number of cells firing AP bursts compared to WT. This gain-of-function phenotype was caused by reduced functional activation of Ca-dependent K currents. Additionally, despite the reduced HVCC Ca influx, the intracellular Ca transients and vesicle exocytosis or endocytosis were unaltered in αδ-1 MCCs compared to WT during sustained stimulation. In conclusion, our study shows that αδ-1 genetic deletion reduces Ca influx in cultured MCCs but leads to a paradoxical increase in catecholamine secretion due to increased excitability. KEY POINTS: Deletion of the αδ-1 high voltage-gated Ca channel (HVCC) subunit reduces mouse chromaffin cell (MCC) Ca influx by ∼60% but causes a paradoxical increase in induced excitability. MCC intracellular Ca transients are unaffected by the reduced HVCC Ca influx. Deletion of αδ-1 reduces the immediately releasable pool vesicle exocytosis but has no effect on catecholamine (CA) release in response to sustained stimuli. The increased electrical activity and CA release from MCCs might contribute to the previously reported cardiovascular phenotype of patients carrying αδ-1 loss-of-function mutations.