Pratt, W. S. | bioRxiv Science

bioRxiv2023

The interplay between splicing of exons 18a and 47 differentially affects membrane targeting and function of human CaV2.2

N-type calcium channels (CaV2.2) are predominantly localized in presynaptic terminals, and are particularly important for pain transmission in the spinal cord. Furthermore, they have multiple isoforms, conferred by alternatively-spliced or cassette exons, which are differentially expressed. Here we have examined alternatively-spliced exon47 variants that encode a long or short C-terminus in human CaV2.2. In the Ensembl database, all short exon47-containing transcripts were associated with the absence of exon 18a, therefore we also examined effect of inclusion or absence of exon18a, combinatorially with the exon47 splice variants. We found that long exon47, only in the additional presence of exon18a, results in CaV2.2 currents that have a 3.6-fold greater maximum conductance than the other three combinations. In contrast, cell surface expression of CaV2.2 in both tsA-201 cells and hippocampal neurons is increased [~]4-fold by long exon47 relative to short exon47, in either the presence or absence of exon18a. This surprising discrepancy between trafficking and function indicates that cell surface expression is enhanced by long exon47, independently of exon 18a. However, in the presence of exon47, exon18a mediates an additional permissive effect on CaV2.2 gating. We also investigated the SNP in exon47 that has been linked to schizophrenia and Parkinsons disease, which we found is only non-synonymous in the short exon47 C-terminal isoform, resulting in two minor alleles. This study highlights the importance of investigating the combinatorial effects of exon inclusion, rather than each in isolation, in order to increase our understanding of calcium channel function. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=150 SRC="FIGDIR/small/557884v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@132c8fborg.highwire.dtl.DTLVardef@12910ccorg.highwire.dtl.DTLVardef@10de072org.highwire.dtl.DTLVardef@a86f7_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

T-type Ca2+ and persistent Na+ currents synergistically elevate ventral, not dorsal, entorhinal cortical stellate cell excitability

The medial entorhinal cortex (mEC) plays a salient role in physiological processes such as spatial cognition and spatial coding. mEC layer II stellate neurons, in particular, influence these processes. Interestingly, ventral and dorsal stellate neurons diversely affect these processes and have distinct intrinsic membrane properties and action potential firing patterns. Little, though, is known about how ventral stellate neuron intrinsic excitability is regulated. We show that ventral stellate neurons predominantly possess T-type Ca2+ currents encoded by CaV3.2 subunits, with dorsal stellate neurons having small or no currents. Further, twice as much CaV3.2 mRNA was present in ventral than dorsal mEC. In line with T-type, CaV3.2 Ca2+ current biophysical properties, depolarising stimuli activated these currents in ventral, but not dorsal, neurons. Here, these currents acted in concert with persistent Na+ currents to elevate input resistance and tonic action potential firing. CaV3.2 currents also enhanced excitatory post-synaptic potential decay and integration solely in ventral neurons. These results reveal that CaV3.2 currents, together with persistent Na+ currents, impart the characteristic intrinsic membrane and firing properties of ventral stellate neurons. This signifies that specific voltage-gated conductances distinctly affect ventral and dorsal mEC stellate neuron activity and functions such as spatial memory and spatial navigation.

neuroscience↗