Alternative pre-mRNA splicing predominates in the nervous systems of complex organisms including humans dramatically expanding the potential size of the proteome. Cell-specific alternative pre-mRNA splicing is thought to optimize protein function for specialized cellular tasks, but direct evidence for this is limited. Transmission of noxious thermal stimuli relies on the activity of N-type CaV2.2 calcium channels in nociceptors. Using an exon replacement strategy in mice, we show that mutually exclusive splicing in the CaV2.2 gene modulates N-type channel function in nociceptors leading to a change in morphine analgesia. Exon 37a enhances μ-opioid receptor mediated inhibition of N-type calcium channels by promoting activity-independent inhibition. In the absence of e37a spinal morphine analgesia is weakened in vivo without influencing the basal response to noxious thermal stimuli. Our data suggest that highly specialized, discrete cellular responsiveness in vivo can be attributed to alternative splicing events regulated at the level of individual neurons.

Neuronal voltage-gated calcium channels generate rapid, transient intracellular calcium signals in response to membrane depolarization. Neuronal CaV channels regulate a range of cellular functions and are implicated in a variety of neurological and psychiatric diseases including epilepsy, Parkinson’s disease, chronic pain, schizophrenia, and bipolar disorder. Each mammalian Cacna1 gene has the potential to generate tens to thousands of CaV channels by alternative pre-mRNA splicing, a process that adds fine granulation to the pool of CaV channel structures and functions. The precise composition of CaV channel splice isoform mRNAs expressed in each cell are controlled by cell-specific splicing factors. The activity of splicing factors are in turn regulated by molecules that encode various cellular features, including cell-type, activity, metabolic states, developmental state, and other factors. The cellular and behavioral consequences of individual sites of CaV splice isoforms are being elucidated, as are the cell-specific splicing factors that control splice isoform selection. Altered patterns of alternative splicing of CaV pre-mRNAs can alter behavior in subtle but measurable ways, with the potential to influence drug efficacy and disease severity. This article is part of a Special Issue entitled: Calcium channels.

CACNA1I is a candidate schizophrenia risk gene. It encodes the pore-forming human CaV3.3 α1 subunit, a subtype of voltage-gated calcium channel that contributes to T-type currents. Recently, two de novo missense variations, T797M and R1346H, of hCaV3.3 were identified in individuals with schizophrenia. Here we show that R1346H, but not T797M, is associated with lower hCaV3.3 protein levels, reduced glycosylation, and lower membrane surface levels of hCaV3.3 when expressed in human cell lines compared to wild-type. Consistent with our biochemical analyses, whole-cell hCaV3.3 currents in cells expressing the R1346H variant were ~50% of those in cells expressing WT hCaV3.3, and neither R1346H nor T797M altered channel biophysical properties. Employing the NEURON simulation environment, we found that reducing hCaV3.3 current densities by 22% or more eliminates rebound bursting in model thalamic reticular nucleus (TRN) neurons. Our analyses suggest that a single copy of Chr22: 39665939G > A CACNA1I has the capacity to disrupt CaV3.3 channel-dependent functions, including rebound bursting in TRN neurons, with potential implications for schizophrenia pathophysiology.