Evidence for involvement of the voltage-dependent Na+ channel gating in depolarization-induced activation of G-proteins.
Evidence for activation of pertussis-toxin-sensitive G-proteins by membrane depolarization in rat brainstem synaptoneurosomes was recently reported (Cohen-Armon, M., and Sokolovsky, M. (1991) J. Biol. Chem. 266, 2595-2605; (1991) Neurosci. Lett. 126, 87-90) and is further supported in this study by the observation that the depolarization-induced effect is inhibited when G-proteins are stabilized in the non-activated state with guanosine 5'-O-(2-thiodiphosphate) (GDP beta S), which was introduced into synaptoneurosomes during the process of permeabilization and resealing. In the present study, agents that either keep the voltage-dependent Na+ channel in persistently activated state (while Na+ currents are blocked) or prevent it from activation were used in an attempt to determine whether the voltage-dependent Na+ channels are involved in the depolarization-induced activation of pertussis-toxin-sensitive G-proteins. The main probe employed was the cardiotonic and antiarrhythmic agent DPI, which is a racemic mixture of two enantiomers, one of which (the R enantiomer) reportedly prevents depolarization-induced activation of the Na+ channel while the other (the S enantiomer) inhibits Na+ channel inactivation. The results suggest that while inactivation of the voltage-dependent Na+ channel does not interfere with the putative depolarization-induced activation of G-proteins, membrane depolarization affects G-proteins and the coupled muscarinic receptors only if the voltage-dependent Na+ channels are capable of being activated. Thus, inhibition of the depolarization-induced activation of Na+ channels was accompanied by inhibition of the depolarization-induced activation of pertussis-toxin-sensitive G-proteins and by modifications of both the coupling of G-proteins to muscarinic receptors and the ADP-ribosylation of Go-proteins. These effects could be counteracted by persistent activation of the voltage-dependent Na+ channels (while Na+ current was blocked). Our observations may suggest that the voltage-dependent Na+ channel gating is involved in the depolarization-induced activation of pertussis toxin-sensitive G-proteins and may provide evidence for a possible mechanism of membrane depolarization signal transduction in excitable cells.
Cohen-Armon
M
M
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
Sokolovsky
M
M
D000109:Acetylcholine / Q000378:metabolism*; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001933:Brain Stem / Q000502:physiology*; D002038:Bungarotoxins / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D015640:Ion Channel Gating; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008970:Molecular Weight; D009474:Neurons / Q000502:physiology; D037342:Pertussis Toxin; D010879:Piperazines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015222:Sodium Channels / Q000502:physiology*; D013237:Stereoisomerism; D013574:Synaptosomes / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000889:Anti-Arrhythmia Agents; D002038:Bungarotoxins; D010879:Piperazines; D011976:Receptors, Muscarinic; D015222:Sodium Channels; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D000246:Adenosine Diphosphate Ribose; D006165:Guanylyl Imidodiphosphate; D013779:Tetrodotoxin; C023427:guanosine 5'-O-(2-thiodiphosphate); D006160:Guanosine Triphosphate; C046261:DPI 201-106; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000109:Acetylcholine