Dynorphin A and cAMP-dependent protein kinase independently regulate neuronal calcium currents.
The kappa-selective opioid peptide dynorphin A (DYN) inhibits neuronal adenylate cyclase activity and reduces neuronal voltage-dependent calcium currents. It is not yet known, however, whether the regulation of calcium channel activity is dependent on or independent of the adenylate cyclase/cAMP system. We used the whole-cell variation of the patch clamp technique to show that DYN reversibly reduced, in a naloxone-sensitive manner, calcium currents in acutely dissociated rat nodose ganglion neurons. DYN slowed the rate of current activation and had a greater effect on currents evoked from relatively negative holding potentials. These actions were mimicked by guanosine 5'-[gamma-thio]triphosphate, which activates GTP-binding proteins (G proteins), and were blocked by pretreatment with pertussis toxin, which inactivates Gi- and Go-type G proteins. In contrast, calcium currents recorded in the presence of the catalytic subunit of the cAMP-dependent protein kinase (AK-C), included in the recording pipette, increased in magnitude throughout the recording. DYN was applied to neurons before and after the effect of AK-C became apparent; the reduction of calcium currents by DYN was greater in the presence of AK-C than in its absence. We conclude that the acute reduction of neuronal calcium currents by DYN occurred by means of activation of pertussis toxin-sensitive Gi- or Go-type G proteins. The persistence of the action of DYN in the presence of AK-C indicates, however, that this effect was independent of a reduction of the activity of the adenylate cyclase/cAMP system and suggests in addition that phosphorylated channels may be preferentially inhibited by DYN.
Gross
R A
RA
Department of Neurology, University of Michigan Medical Center, Ann Arbor 48104.
Moises
H C
HC
Uhler
M D
MD
Macdonald
R L
RL
D037361:Adenylate Cyclase Toxin; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004399:Dynorphins / Q000494:pharmacology*; D004594:Electrophysiology / Q000379:methods; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006706:Homeostasis; D007700:Kinetics; D046911:Macromolecular Substances; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009620:Nodose Ganglion / Q000502:physiology*; D037342:Pertussis Toxin; D011494:Protein Kinases / Q000502:physiology*; D051381:Rats; D013873:Thionucleotides / Q000494:pharmacology; D014630:Vagus Nerve / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D015220:Calcium Channels; D046911:Macromolecular Substances; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D009270:Naloxone; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004399:Dynorphins; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D011494:Protein Kinases