Calcium Channel β Subunits Differentially Regulate the Inhibition of N-type Channels by Individual Gβ Isoforms

Abstract

The direct inhibition of N-and P/Q-type calcium channels by G protein ␤␥ subunits is considered a key mechanism for regulating presynaptic calcium levels. We have recently reported that a number of features associated with this G protein inhibition are dependent on the G protein ␤ subunit isoform (Arnot, M. I., Stotz, S. C., Jarvis, S. E., Zamponi, G. W. Chem. 275, 40777-40781). Here, we have examined the abilities of different types of ancillary calcium channel ␤ subunits to modulate the inhibition of ␣ 1B N-type calcium channels by the five known different G␤ subunit subtypes. Our data reveal that the degree of inhibition by a particular G␤ subunit is strongly dependent on the specific calcium channel ␤ subunit, with N-type channels containing the ␤ 4 subunit being less susceptible to G␤␥-induced inhibition. The calcium channel ␤ 2a subunit uniquely slows the kinetics of recovery from G protein inhibition, in addition to mediating a dramatic enhancement of the G protein-induced kinetic slowing. For G␤ 3 -mediated inhibition, the latter effect is reduced following site-directed mutagenesis of two palmitoylation sites in the ␤ 2a N-terminal region, suggesting that the unique membrane tethering of this subunit serves to modulate G protein inhibition of N-type calcium channels. Taken together, our data suggest that the nature of the calcium channel ␤ subunit present is an important determinant of G protein inhibition of N-type channels, thereby providing a possible mechanism by which the cellular/subcellular expression pattern of the four calcium channel ␤ subunits may regulate the G protein sensitivity of N-type channels expressed at different loci throughout the brain and possibly within a neuron.The inhibition of presynaptic calcium channels by the activation of seven-helix transmembrane receptors is an important mechanism for modulating calcium influx into presynaptic nerve termini. It is now well established that this inhibitory mechanism occurs via a direct interaction between the G protein ␤␥ dimer and the calcium channel ␣ 1 subunit (Refs. 1 and 2; for review, see Ref.3). Upon G␤␥ binding, the channels experience an increase in first latency to opening (4), which is seen as a decrease in peak current amplitude, a slowing of the time course of activation, and a slowed macroscopic time course of inactivation at the whole cell level. The inhibition can be relieved by application of a strong depolarizing voltage prepulse (5), which causes a transient dissociation of the G protein complex from the channel (6) and, consequently, a temporary restoration of normal current kinetics. The overall degree of inhibition is strongly dependent not only on the nature of the calcium channel ␣ 1 subunit (7-10), but also on the G␤ subunit subtype (10 -12). The notion of a G␤ subunit isoform dependence of this G protein effect is also supported by the observation that protein kinase C is able to antagonize the inhibition of N-type calcium channels by G␤ 1 subunits, but not that mediated by other G␤ subunit isoforms (13).It is ...

Deletion of N-Type Calcium Channels Alters Ethanol Reward and Reduces Ethanol Consumption in Mice

“…Consistent with the importance of these receptors in ethanol selfadministration is the finding that mice deficient in CB1 cannabinoid (Naassila et al, 2004), -opioid (Roberts et al, 2000) or D2 dopamine receptors (Phillips et al, 1998) consume less alcohol than wild-type littermates. Activation of these receptors can inhibit N-type calcium channels through release of ␤␥ subunits (Feng et al, 2001), which appear to be important in promoting ethanol self-administration (Yao et al, 2002).…”

“…The principal defined role for N-type calcium channels, along with P/Qtype channels, is in the regulation of evoked neurotransmitter release (Reid et al, 2003). The function of N-type channels is inhibited by ␤␥ subunits of heterotrimeric G-proteins (Feng et al, 2001). Accordingly, N-type channels are regulated by several neuropeptides, neuromodulators, and neurotransmitters that bind to G-protein-coupled receptors, such as opioids, cannabinoids, and dopamine (Twitchell et al, 1997;Momiyama and Koga, 2001;Kitamura et al, 2002).…”

G protein inhibition of CaV2 calcium channels

“…124 Furthermore, at least some of the distinct effects of Ca V β 2a on modulation are linked to its palmitoylation. 124,149 In part this might be due to an effective concentration of the subunit at the plasma membrane, but other actions might also contribute. For example, the effects of Ca V β on channel kinetics are dependent on its orientation relative to the α 1 subunit.…”

“…In this context it is pertinent to note that previous work has shown the subtype of Ca V β can influence the extent and kinetics of Gβγ-mediated inhibition. 148,149 Moreover, the particular effects of the Ca V β subunits are dependent on the identity of the G protein β subunit involved in producing the inhibition. 149 Thus, the inhibition is precisely tuned by the identity of both the Ca V β and G protein β subunits.…”

Ginsenoside Rb1 selectively inhibits the activity of L-type voltage-gated calcium channels in cultured rat hippocampal neurons

“…L-, N-, and P/Q-type Ca 2+ channels are pharmacologically identified and characterized by their specific blockers. Nifedipine is an L-type Ca 2+ channel inhibitor, ω-conotoxin GVIA is an N-type Ca 2+ channel inhibitor, and ω-agatoxin IVA is a P/Q-type Ca 2+ channel inhibitor [4][5][6][7][8][9] . Because the elevation of intracellular Ca 2+ levels ([Ca 2+ ] i ) caused by the excessive stimulation of Ca 2+ channels plays a key role in the excitotoxic damage of neurons, agents blocking the elevation of [Ca 2+ ] i by regulating Ca 2+ channels might have neuroprotective effects [10][11][12] .…”