Contribution of the kinetics of G protein dissociation to the characteristic modifications of N-type calcium channel activity

Neurosci Res. 2006 Nov;56(3):332-43. doi: 10.1016/j.neures.2006.08.002. Epub 2006 Sep 12.

Abstract

Direct G protein inhibition of N-type calcium channels is recognized by characteristic biophysical modifications. In this study, we quantify and simulate the importance of G protein dissociation on the phenotype of G protein-regulated whole-cell currents. Based on the observation that the voltage-dependence of the time constant of recovery from G protein inhibition is correlated with the voltage-dependence of channel opening, we depict all G protein effects by a simple kinetic scheme. All landmark modifications in calcium currents, except inhibition, can be successfully described using three simple biophysical parameters (extent of block, extent of recovery, and time constant of recovery). Modifications of these parameters by auxiliary beta subunits are at the origin of differences in N-type channel regulation by G proteins. The simulation data illustrate that channel reluctance can occur as the result of an experimental bias linked to the variable extent of G protein dissociation when peak currents are measured at various membrane potentials. To produce alterations in channel kinetics, the two most important parameters are the extents of initial block and recovery. These data emphasize the contribution of the degree and kinetics of G protein dissociation in the modification of N-type currents.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analgesics, Opioid / pharmacology
  • Animals
  • Calcium Channels, N-Type / physiology*
  • Dose-Response Relationship, Drug
  • Dose-Response Relationship, Radiation
  • Electric Stimulation / methods
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / pharmacology
  • GTP-Binding Protein beta Subunits / genetics
  • GTP-Binding Protein beta Subunits / metabolism
  • GTP-Binding Proteins / antagonists & inhibitors
  • GTP-Binding Proteins / chemistry*
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Membrane Potentials / radiation effects
  • Microinjections / methods
  • Models, Neurological
  • Oocytes
  • Patch-Clamp Techniques / methods
  • Rabbits
  • Rats
  • Receptors, Opioid, mu / genetics
  • Receptors, Opioid, mu / metabolism
  • Xenopus

Substances

  • Analgesics, Opioid
  • Calcium Channels, N-Type
  • GTP-Binding Protein beta Subunits
  • Receptors, Opioid, mu
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
  • GTP-Binding Proteins