Age-Dependent Contribution of P/Q- and R-Type Ca²⁺Channels to Neuromuscular Transmission inLethargicMice

Abstract

b-Subunits of voltage-gated calcium channels (VGCCs) regulate assembly and membrane localization of the pore-forming a 1 -subunit and strongly influence channel function. b 4 -Subunits normally coassociate with a 1A -subunits which comprise P/Q-type (Ca v 2.1) VGCCs. These control acetylcholine (ACh) release at adult mammalian neuromuscular junctions (NMJs). The naturally occurring lethargic (lh) mutation of the b 4 -subunit in mice causes loss of the a 1 -binding site, possibly affecting P/Q-type channel expression or function, and thereby ACh release. End-plate potentials and miniature end-plate potentials were recorded at hemidiaphragm NMJs of 5-7-week and 3-5-month-old lh and wild-type (wt) mice. Sensitivity to antagonists of P/Q-[v-agatoxin IVA (v-Aga-IVA)], L-(nimodipine), N-(v-conotoxin GVIA), and R-type [C 192 H 274 N 52 O 60 S 7 (SNX-482)] VGCCs was compared in juvenile and adult lh and wt mice. Quantal content (m) of adult, but not juvenile, lh mice was reduced compared to wt. v-Aga-IVA (~60%) and SNX-482 (~45%) significantly reduced m in adult lh mice. Only Aga-IVA affected wt adults. In juvenile lh mice, v-Aga-IVA and SNX-482 decreased m by .75% and~20%, respectively. Neither v-conotoxin GVIA nor nimodipine affected ACh release in any group. Immunolabeling revealed a 1E and a 1A , b 1 , and b 3 staining at adult lh, but not wt NMJs. Therefore, in lh mice, when the b-subunit that normally coassociates with a 1A to form P/Q channels is missing, P/Q-type channels partner with other b-subunits. However, overall participation of P/Q-type channels is reduced and compensated for by R-type channels. R-type VGCC participation is age-dependent, but is less effective than P/Q-type at sustaining NMJ function.

Sympathomimetics regulate neuromuscular junction transmission through TRPV1, P/Q- and N-type Ca2+ channels

“…A previous study shows that N-type Ca 2+ channels are located at terminals that are immunoreactive to substance P, (Westenbroek et al, 1998) indicating that they are expressed in sympathetic axons, and consistent with reports that they are responsible for transmitter release from peripheral autonomic nerve terminals. (Katz et al, 1996;Katz et al, 2015;Molina-Campos et al, 2015) Since N-type Ca 2+ channels play an essential role in evoked release of NA from sympathetic neurons, (Hirning et al, 1988) synaptic vesicle recycling depends on Ca 2+ , (Neher and Marty, 1982;Schneggenburger et al, 2012;Yamashita et al, 2010) and sympathetic axons run along motor axons in spinal nerves, we propose that ω-conotoxin GIVA blockade of the neurotransmitter NA from sympathetic axons counters the time-and frequency-dependent decline in EPP amplitude.…”

“…P/Q-type Ca 2+ channels are involved in ACh release from adult mammalian motor nerve terminals, and the N-type is responsible for transmitter release from peripheral autonomic nerve terminals. (Katz et al, 1996;Katz et al, 2015;Molina-Campos et al, 2015) Treating the peroneal nerve/lumbricalis muscle preparation with ω-agatoxin IVA, a P/Q-type Ca 2+ channel blocker, sharply reduced the LP/FP EPP amplitude ratio at various nerve stimulation frequencies (2-50Hz). This effect is similar to that recorded in Lambert-Eaton Myasthenic Syndrome (LEMS), (Lambert and Elmqvist, 1971) which involves antibodies against P/Qtype Ca 2+ channels.…”

A mutation in CaV2.1 linked to a severe neurodevelopmental disorder impairs channel gating

“…1, C and D, insets), because these subunits promote membrane expression of the α 1A subunit in this heterologous system (Meza and Adams, 1998). In particular, we chose the β 4 isoform because of its overlapping expression with Ca V 2.1 at NMJs (Pagani et al, 2004; Molina-Campos et al, 2015) and in multiple cell types within the cerebellum (Volsen et al, 1997).…”

Possible Involvement of the CACNA1E Gene in Migraine: A Search for Single Nucleotide Polymorphism in Different Clinical Phenotypes

“…The carbonic anhydrase inhibitor acetazolamide that is able to normalize the impairment of neuromuscular transmission inhibits by 30% Ca v 2.3 currents in vitro . R‐type Ca v 2.3 Ca 2+ channels play a role at the neuromuscular junction and can compensate for defective acetylcholine release due to mutated P/Q Ca v 2.1 Ca2 + with a loss of function in tottering and lethargic mice mutants . One cannot exclude therefore that a dysfunction of R‐type channels might contribute to the NMJ abnormalities found in subgroups of MA patients.…”

“…46 R-type Ca v 2.3 Ca 21 channels play a role at the neuromuscular junction and can compensate for defective acetylcholine release due to mutated P/Q Ca v 2.1 Ca2 1 with a loss of function in tottering 47 and lethargic mice mutants. 48 One cannot exclude therefore that a dysfunction of R-type channels might contribute to the NMJ abnormalities found in subgroups of MA patients. Another subclinical abnormality reported in migraine patients concerns the vestibulo-cerebellar system.…”