UBC Theses and Dissertations
The contributions of Cav2.1 alternative splicing and calcium-dependent modulation to congenital migraine Adams, Paul Jacob
Cav2.1 calcium (Ca²⁺) channels are expressed throughout the mammalian central nervous system where they mediate P/Q-type Ca²⁺ currents essential for neurotransmitter release at most fast synapses. In humans, naturally occurring mutations in the CACNA1A gene encoding Cav2.1 are associated with several severe congenital disorders including familial hemiplegic migraine type 1 (FHM-1). Alternative splicing of the Cav2.1 transcript generates multiple functionally distinct channel variants with unique spatial and temporal expression patterns. Yet, whether different Cav2.1 splice variants have distinct responses to FHM-1 missense mutations that relate to the localized, episodic nature of the FHM-1 phenotype has not been explored. Using recombinant Cav2.1 channels, we systematically compared the biophysical effects of three FHM-1 mutations in two prevalent Cav2.1 splice variants. All three FHM-1 mutations caused differential effects on voltage-dependent and kinetic properties when expressed in the short carboxyl terminus variant (Cav2.1 Δ47) compared to the long variant (Cav2.1 +47). Our findings provide important insight concerning the role of Cav2.1 alternative splicing and the pathophysiology of FHM-1. Ca²⁺-dependent facilitation (CDF) of Cav2.1 channels is a powerful means of channel control proposed to play a role in short-term facilitation of synaptic release during repetitive action potentials (APs). However, empirical evidence to support CDF of Cav2.1 as a relevant mechanism of synaptic facilitation in the CNS is limited. As such, short-term facilitation of synaptic release is generally attributed to enhanced vesicle release due to residual Ca²⁺ binding to sensor proteins that directly mediate vesicle fusion and transmitter release. However, we found that two FHM-1 mutations occluded CDF of Cav2.1 in both recombinant and native systems and cause a corresponding attenuation in short-term synaptic facilitation at the cerebellar parallel fibre to Purkinje synapse. This is the first evidence that presynaptic Ca²⁺ at this fast central synapse also enhances Ca²⁺ influx through Cav2.1 by means of CDF and acts as an additional required mechanism for short-term plasticity. Thus, the data supports the notion that CDF of Cav2.1 underlies key aspects of short-term plasticity in the CNS and provides the first evidence that FHM-1 mutations directly affect Cav2.1 CDF.
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