Abstract
We report expression system-dependent effects of heterozygous mutations (P769L and A1059S) in the Cav3.2 CACNA1H gene identified in a pediatric patient with chronic pain and absence seizures. The mutations were introduced individually into recombinant channels and then analyzed by means of electrophysiology. When both mutants were co-expressed in tsA-201 cells, we observed a loss of channel function, with significantly smaller current densities across a wide range of voltages (-40 to +20 mV). In addition, when both mutant channels were co-expressed, the channels opened at a more depolarizing potential with a ~5-mV right shift in the half-activation potential, with no changes in half-inactivation potential and the rate of recovery from inactivation. Interestingly, when both mutants were co-expressed in the neuronal-derived CAD cells in a different extracellular milieu, the effect was remarkably different. Although not statistically significant (p < 0.07), current densities appeared augmented compared to wild-type channels and the difference in the half-activation potential was lost. This could be attributed to the replacement of extracellular sodium and potassium with tetraethylammonium chloride. Our results show that experimental conditions can be a confounding factor in the biophysical effects of T-type calcium channel mutations found in certain neurological disorders.
Highlights
The CACNA1H gene encodes the pore-forming α1 subunit of the T-type calcium channel isoform Cav3.2 [1]
This feature is important in the thalamocortical network, where T-type channels contribute to its burst firing and oscillatory behavior [3] and are known to play a role in idiopathic generalized epilepsies (IGEs) [4]
A number of mutations in human Cav3.2 channels have been linked to epileptic disorders such as childhood absence epilepsy (CAE), febrile seizures (FS), myoclonic–astatic epilepsy (MAE), and juvenile absence epilepsy (JAE) [5,6,7,8]
Summary
The CACNA1H gene encodes the pore-forming α1 subunit of the T-type calcium channel isoform Cav3.2 [1]. T-type channels are a family of low-voltage-activated (LVA) Ca2+ channels that are important regulators of neuronal excitability They can be activated by small depolarizations of the plasma membrane, and Ca2+ influx through these channels triggers low-threshold spikes that facilitate the generation of Na+-dependent bursts of action potentials [2]. This feature is important in the thalamocortical network, where T-type channels contribute to its burst firing and oscillatory behavior [3] and are known to play a role in idiopathic generalized epilepsies (IGEs) [4]. Upregulation and increased activity of Cav3.2 channels are associated with chronic pain in animal models [14,15,16], no Pflugers Arch - Eur J Physiol mutations in the human CACNA1H Cav3.2 gene have been linked to pain conditions in patients so far
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