Effects of voltage-gated calcium channel subunit genes on calcium influx in cultured C. elegans mechanosensory neurons

Voltage-gated calcium channels (VGCCs) serve as a critical link between electrical signaling and diverse cellular processes in neurons. We have exploited recent advances in genetically encoded calcium sensors and in culture techniques to investigate how the VGCC α₁ subunit EGL-19 and α₂/δ subunit UNC-36 affect the functional properties of C. elegans mechanosensory neurons. Using the protein-based optical indicator cameleon, we recorded calcium transients from cultured mechanosensory neurons in response to transient depolarization. We observed that in these cultured cells, calcium transients induced by extracellular potassium were significantly reduced by a reduction-of-function mutation in egl-19 and significantly reduced by L-type calcium channel inhibitors; thus, a main source of touch neuron calcium transients appeared to be influx of extracellular calcium through L-type channels. Transients did not depend directly on intracellular calcium stores, although a store-independent 2-APB and gadolinium-sensitive calcium flux was detected. The transients were also significantly reduced by mutations in unc-36, which encodes the main neuronal α₂/δ subunit in C. elegans. Interestingly, while egl-19 mutations resulted in similar reductions in calcium influx at all stimulus strengths, unc-36 mutations preferentially affected responses to smaller depolarizations. These experiments suggest a central role for EGL-19 and UNC-36 in excitability and functional activity of the mechanosensory neurons.