The reduction of neuronal calcium currents by ATP-gamma-S is mediated by a G protein and occurs independently of cyclic AMP-dependent protein kinase.
We studied the effects of ATP-gamma-S on the T, N and L calcium current components of nodose ganglion neurons using the whole cell variation of the patch clamp technique. ATP-gamma-S can serve as a phosphate donor in kinase-mediated reactions, the donated phosphate group being resistant to the action of phosphatases. We therefore compared the effect of ATP-gamma-S to that of the catalytic subunit of the cyclic AMP-dependent protein kinase (AK-C), included in the recording pipette with 5 mM ATP. AK-C (50 micrograms/ml) had no effect on the T current, and caused a approximately 30% increase in currents containing the N and L components during a 20-min recording, as compared to a approximately 45% decrease in control currents. In contrast, in the presence of 2.5 mM ATP-gamma-S, T currents declined approximately 30%, and currents containing the N and L components declined to a greater extent than control currents, about 65%. In addition, the time to peak current was increased from approximately 14 ms to approximately 40 ms. This effect of ATP-gamma-S on calcium currents was similar to that of certain neurotransmitters or GTP-gamma-S, an activator of G proteins, except that the effects of ATP-gamma-S were delayed 5-7 min relative to GTP-gamma-S. The effects of both ATP-gamma-S and GTP-gamma-S were reduced or abolished in neurons treated with pertussis toxin. We conclude that AK-C regulates neuronal calcium currents, presumably by phosphorylation of channels or associated proteins, and that the ATP-gamma-S-induced reduction of calcium currents cannot be due to its serving as a phosphate donor for endogenous AK.(ABSTRACT TRUNCATED AT 250 WORDS)
Gross
R A
RA
Department of Neurology, University of Michigan Medical Center, Ann Arbor 48104.
Uhler
M D
MD
Macdonald
R L
RL
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D005071:Evoked Potentials / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009620:Nodose Ganglion / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D037342:Pertussis Toxin; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015220:Calcium Channels; D010566:Virulence Factors, Bordetella; C022571:adenosine 5'-O-(3-thiotriphosphate); D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D011494:Protein Kinases; D019204:GTP-Binding Proteins