Characterization of calcium(v)1.2/1.3 L-type calcium channels in medium spiny neurons of the dorsal striatum

The nuclei of the basal ganglia are important in execution of movement; dysfunction within basal ganglia circuitry is the central cause of several neurological disorders such as Parkinson's disease. Two important modulators of the activity of striatal medium spiny neurons are dopaminergic inputs arising from the substantia nigra and cholinergic inputs arising from striatal interneurons. Previous work from our laboratory has demonstrated that L-type calcium channels are an important target of signaling cascades initiated by dopamine and muscarinic acetylcholine receptors. L-type calcium channel currents are mediated by either Cav1.2 or Cav1.3 alpha 1 subunits, which differ in their pharmacology and biophysics. Thus we sought to determine which of these two channel subtypes were the targets of modulation by dopaminergic (D2) and muscarinic (M1) receptors.; To address this issue we set out to further characterize the Ca v subtypes mediating the L-type calcium channel currents in medium spiny neurons based on their mRNA expression, pharmacology, and channel biophysics. Our results indicated that Cavl.2 and Cav1.3 channels differ in dihydropyridine sensitivity and voltage dependence of activation. Based upon these observations we were able to utilize the differences in nimodipine affinity for Cav1.2 and Cav1.3 as well as use Ca v1.3 knock-out animals to determine which channel subtypes are subject to modulation by dopamine and acetylcholine. Utilizing this strategy, we were able to establish that D2 and M1 receptor agonists preferentially modulate Cav1.3. This result led us to ask in what way is Ca v1.3 distinguished from Cav1.2 in D2/M1 modulation. Our laboratory previously established that L-type calcium channels were modulated by a pertussis-toxin insensitive pathway, resulting in a modulation of the channel by calcineurin. Action by calcineurin is calcium-dependent; thus, we studied the proximity of intracellular calcium release with the Ca v1.3 carboxy-terminal and the importance of scaffolding proteins Shank and Homer in subcellular localization of this pathway. Our questions developed into how the intracellular protein regulator of calcium/calmodulin-dependent signaling affects D2 and M1 modulation of Cav1.3.