Alternative Splicing of the Ca_V1.3 Channel IQ Domain, a Molecular Switch for Ca²⁺-Dependent Inactivation within Auditory Hair Cells

Abstract

Native Ca V 1.3 channels within cochlear hair cells exhibit a surprising lack of Ca 2ϩ -dependent inactivation (CDI), given that heterologously expressed Ca V 1.3 channels show marked CDI. To determine whether alternative splicing at the C terminus of the Ca V 1.3 gene may produce a hair cell splice variant with weak CDI, we transcript-scanned mRNA obtained from rat cochlea. We found that the alternate use of exon 41 acceptor sites generated a splice variant that lost the calmodulin-binding IQ motif of the C terminus. These Ca V 1.3 IQ⌬ ("IQ deleted") channels exhibited a lack of CDI, which was independent of the type of coexpressed ␤-subunits. Ca V 1.3 IQ⌬ channel immunoreactivity was preferentially localized to cochlear outer hair cells (OHCs), whereas that of Ca V 1.3 IQfull channels (IQ-possessing) labeled inner hair cells (IHCs). The preferential expression of Ca V 1.3 IQ⌬ within OHCs suggests that these channels may play a role in processes such as electromotility or activity-dependent gene transcription rather than neurotransmitter release, which is performed predominantly by IHCs in the cochlea.

Switching of Ca2+-Dependent Inactivation of CaV1.3 Channels by Calcium Binding Proteins of Auditory Hair Cells

“…␣ 1C , ␣ 1Dsh , and ␣ 1Dlg sequence numbering (far right) correspond to previously published constructs (Wei et al, 1991; ute to the limited CDI profile in hair cells. In our companion paper (Shen et al, 2006), a different ␣ 1D splice variant is described, one that both lacks CDI and shows expression in OHCs of the mammalian cochlea.…”

“…Given these biological considerations and the propensity for recombinant Ca V 1.3 channels to undergo CDI (Xu and Lipscombe, 2001), discernment of the mechanisms for diminished hair-cell CDI represents an interesting issue for auditory neurobiology. This paper and its companion (Shen et al, 2006) investigated the extreme CDI malleability of Ca V 1.3 channels, particularly its moderation in the auditory setting. Is the CDI of these channels mediated by calmodulin (CaM), as for several other Ca V 1 and Ca V 2 Ca 2ϩ channels ?…”

Post-transcriptional modifications and “Calmodulation” of voltage-gated calcium channel function: Reflections by two collaborators of David T Yue

“…25 The Striessnig's group has observed such a phenomenon in their human clone but for those who conducted experiments with the Lipscombe's rat clone, the rat long-form Ca V 1.3 42 clone did produce robust CDI. 21,26,27 Besides alternative splicing altering Ca V 1.3 channel electrophysiological properties, we have shown recently the mechanism for influencing DHP-sensitivity in Ca V 1.3 is completely different from that exhibited by the Ca V 1.2 channels. We discovered that the mutually exclusive exons 8/8a have no effect on Ca V 1.3 DHP-sensitivity while instead the binding of calmodulin (CaM) influenced DHP sensitivity.…”

“…The Cav1.3 IQD channels were determined by immuno-labeling to be preferentially localized on the outer hair cells (OHCs). 21 The lack of focal expression of the Cav1.3 IQD channels suggests the potential contribution of these channels to both neurotransmitter release and motility of the OHCs. This work was done in collaboration with Paul Fuchs in which Dave and I were privileged to be co-Investigator on Paul's NIH grant.…”

Neuromedin U Type 1 Receptor Stimulation of A-type K+ Current Requires the βγ Subunits of Go Protein, Protein Kinase A, and Extracellular Signal-regulated Kinase 1/2 (ERK1/2) in Sensory Neurons

“…For example, mutually exclusive splicing patterns in the Cav2.2 gene modulate N-type channel function in nociceptors, leading to a change in morphine analgesia (42). Furthermore, alternative splicing of the Cav1.3 channel IQ domain generates a molecular switch for Ca 2ϩ -dependent inactivation within auditory hair cells (43). PKC-mediated responses are also shown to be tissue specific.…”