Substance P and somatostatin inhibit calcium channels in rat sympathetic neurons via different G protein pathwavs

1. We studied the mechanism of voltage-dependent inhibition of N-type calcium current by norepinephrine (NE) and vasoactive intestinal peptide (VIP) in adult rat superior cervical ganglion (SCG) neurons using the whole cell patch-clamp technique. 2. The voltage dependence of inhibition is manifest in the reversal of inhibition by strong depolarization. We tested the hypothesis that this voltage dependence results from disruption of G proteins binding to calcium channels. According to this hypothesis, the kinetics of calcium current reinhibition following a strong depolarization should become faster for higher concentrations of active G proteins. 3. Assuming that larger inhibitions result from higher concentrations of active G proteins, we used different concentrations of NE to alter the amplitude of inhibition and, thus, the active G protein concentration. We found that the kinetics of reinhibition at -80 mV following a depolarizing pulse to +80 mV were faster for larger inhibitions. 4. VIP induces voltage-dependent inhibition of N-current via a different G protein (Gs) than that of NE (Go). We found that the effect of VIP on reinhibition kinetics was identical to that produced by NE. 5. Combined application of NE and VIP did not greatly increase the amplitude of the inhibition but significantly increased the rate of reinhibition. Thus NE plus VIP appear to greatly increase the concentration of the molecule binding to the channel (G protein according to the hypothesis). 6. The kinetics of calcium current disinhibition during strong depolarization (step to +80 mV) did not change with the size of the inhibition induced by NE, VIP or application of NE and VIP together. 7. Both the concentration-dependent reinhibition kinetics and concentration-independent disinhibition kinetics are consistent with the hypothesis that active G proteins bind directly to N-type calcium channels to modulate their activity in rat sympathetic neurons.

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Calcineurin Modulates G Protein-Mediated Inhibition of N-Type Calcium Channels in Rat Sympathetic Neurons

Journal of Neurophysiology ◽

10.1152/jn.1997.78.2.1161 ◽

1997 ◽

Vol 78 (2) ◽

pp. 1161-1169 ◽

Cited By ~ 28

Author(s):

Yu Zhu ◽

Jerrel L. Yakel

Keyword(s):

Calcium Channels ◽

G Protein ◽

Sympathetic Neurons ◽

Somatostatin Receptor ◽

Male Rat ◽

Patch Clamp Recording ◽

Whole Cell Patch Clamp ◽

Major Pelvic Ganglion ◽

G Protein Coupled ◽

Kinetics Of

Zhu, Yu and Jerrel L. Yakel. Calcineurin modulates G protein-mediated inhibition of N-type calcium channels in rat sympathetic neurons. J. Neurophysiol. 78: 1161–1169, 1997. The modulation of N-type voltage-gated calcium (Ca2+) channels by G protein-coupled receptors was investigated in sympathetic neurons of the male rat major pelvic ganglion (MPG) with the use of whole cell patch-clamp recording techniques from acutely dissociated neurons. By inhibiting calcineurin, a Ca2+/calmodulin-regulatedprotein phosphatase, the α2 noradrenergic and somatostatin receptor-induced inhibition of these N-type Ca2+ channels was greatly reduced. Both of these receptor pathways utilize a pertussis toxin-sensitive G protein (GPTX). The guanosine 5′-o-(3-thiotriphosphate) (GTPγS)-induced decrease in the amplitude and activation kinetics of Ca2+ currents, an effect that was similar to the activation of GPTX-coupled receptors, also was reduced by the inhibition of calcineurin. Calcineurin does not regulate the muscarinic receptor-induced inhibition of the N-type Ca2+ channels, a pathway that utilizes a different G protein in the MPG neurons. Thus calcineurin appears to selectively regulate the coupling between the GPTX and the Ca2+ channel.

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