Altered Gating of Two Ca2.1 Variants Linked to Neurodevelopmental Disorders With Epilepsy and Migraine.

P/Q-type (Ca2.1) Ca channels regulate the release of neurotransmitter at central synapses. Missense and nonsense mutations in CACNA1A, the gene that encodes the principal α subunit of the Ca2.1 channel complex, are well-known to cause Episodic Ataxia type 2 (EA2) and Familial Hemiplegic Migraine type 1 (FHM1). These Ca2.1 channelopathies are typically caused by either channel loss/reduction-of-function (LOF) or gain-of-function (GOF), respectively. However, recent genome-wide sequencing has revealed that point mutations in Ca2.1, in fact, underlie a spectrum of neurological disorders that feature epilepsy, tremor, nystagmus, hypotonia, cerebellar atrophy, cognitive deficits, and global developmental delay. Given the multiple manifestations of the mutations and the broad range of severity among these disorders, the assessment of the impact of an individual pathological mutation on channel function is essential for understanding the etiology of a given case. To this end, we expressed the rat orthologues of one newly identified and one previously reported, but yet to be characterized, human Ca2.1 variants (V176M and R1673C, respectively) in HEK 293 cells and investigated their biophysical properties using patch-clamp electrophysiology. The corresponding rat variants (V178M and R1624C, respectively) had multiple effects on channel function, though each mutation affected channel gating differently. V178M displayed a ~10 mV hyperpolarizing shift in activation and slowed deactivation, while R1624C slowed channel activation kinetics, delayed closure, and accelerated recovery from inactivation. Molecular modeling revealed structural alterations that may account for the observed changes in channel gating. Taken together, our results indicate that V176M and R1673C likely cause human Ca2.1 channelopathies through multiple, distinct mechanisms.