Identification of Functionally Distinct Isoforms of the N-Type Ca2+ Channel in Rat Sympathetic Ganglia and Brain

Abstract

The N channel is critical for regulating release of neurotransmitter at many synapses, and even subtle differences in its activity would be expected to influence the efficacy of synaptic transmission. Although several splice variants of the N channel are expressed in the mammalian nervous system, their biological importance is presently unclear. Here, we show that variants of the alpha1B subunit of the N channel are expressed in sympathetic ganglia and that alternative splicing within IIIS3-S4 and IVS3-S4 generate kinetically distinct channels. We further show a striking difference between the expression pattern of the S3-S4 variants in brain and peripheral ganglia and conclude that the brain-dominant form of the N channel gates 2-to-4-fold more rapidly than that predominant in ganglia.

Control of gating mode by a single amino acid residue in transmembrane segment IS3 of the N-type Ca 2+ channel

“…In contrast, Ca v 2.2a activates and inactivates slowly ( act ϭ 46.6 Ϯ 5.3 ms, n ϭ 6; inact ϭ 264 Ϯ 28 ms, n ϭ 6). In addition to this kinetic difference, the midpoint of the conductance-voltage curve of Ca v 2.2a is more positive (V a ϭ 54.2 Ϯ 2.2 mV, n ϭ 16; (30,31). However, these sequence differences are not responsible for the major change in the rate and voltage dependence of activation illustrated in Fig.…”

“…Several different isoforms of Ca v 2.2 sharing Ͼ90% overall sequence identity have been cloned and functionally characterized (4,5,(27)(28)(29)(30)(31). N-type Ca 2ϩ channels cloned from rat brain have two isoforms, Ca v 2.2a and Ca v 2.2b originally designated rbB-I and rbB-II (4,27,29).…”

Old proteins, developing roles: The regulation of calcium channels by synaptic proteins

“…141 C-terminal splicing of exon e37a results in selective targeting to small nociceptive neurons. 142,143 Ca V 2.2 and Ca V 2.3 splice variants containing e18a appear to be both spatially and developmentally regulated, with increasing expression in Ca V 2.2 and decreasing expression in Ca V 2.3 over time. 137 Together, these studies suggest that such alterations in calcium channel sequence due to mRNA splicing that alter not only intrinsic channel properties but also the regulatory influences of certain …”

Chronic ethanol exposure induces an N‐type calcium channel splice variant with altered channel kinetics

“…These changes in mRNA were associated with kinetic changes consistent with increased relative abundance of a 1 2.2 subunits that lack ET [6,7]. Since ET-containing variants are expressed primarily in the peripheral nervous system, such a shift in ET variant expression might contribute to increases in sympathetic nervous system activity and increased levels of circulating catecholamines associated with withdrawal from alcohol [14].…”

“…The tetrapeptide SFMG in IVS3-4 is encoded by exon 24a and when present shifts the voltage dependence of activation by about 2 mV to more positive potentials [6]. The dipeptide Glu-Thr (ET) in IVS3-4 linker is encoded by exon 31a, and when present slows the rate of channel opening and shifts the voltage dependence of channel activation by $6 mV to more depolarized voltages [6,7].…”