Kinetics of ion channel modulation by cAMP in rat hippocampal neurones.
Ion channel regulation by cyclic AMP and protein kinase A is a major effector mechanism for monoamine transmitters and neuromodulators in the CNS. Surprisingly, there is little information about the speed and kinetic limits of cAMP-PKA-dependent excitability changes in the brain. To explore these questions, we used flash photolysis of caged-cAMP (DMNB-cAMP) to provide high temporal resolution. The resultant free cAMP concentration was calculated from separate experiments in which this technique was used, in excised patches, to activate cAMP-sensitive cyclic nucleotide-gated (CNG) channels expressed in Xenopus oocytes. In hippocampal pyramidal neurones we studied the modulation of a potassium current (slow AHP current, I(sAHP)) known to be targeted by multiple transmitter systems that use cAMP-PKA. Rapid cAMP elevation by flash photolyis of 200 microm DMNB-cAMP completely inhibited the K(+) current. The estimated yield (1.3-3%) suggests that photolysis of 200 microm caged precursor is sufficient for full PKA activation. By contrast, extended gradual photolysis of 200 microm DMNB-cAMP caused stable but only partial inhibition. The kinetics of rapid cAMP inhibition of the K(+) conductance (time constant 1.5-2 s) were mirrored by changes in firing patterns commencing within 500 ms of rapid cAMP elevation. Maximal increases in firing were short-lasting (< 60 s) and gave way to moderately enhanced levels of spiking. The results demonstrate how the fidelity of phasic monoamine signalling can be preserved by the cAMP-PKA pathway.
Lancaster
Barrie
B
Wolfson Institute for Biomedical Research, University College London, Gower Street, London WC1E 6BT, UK. b.lancaster@ucl.ac.uk
Hu
Hua
H
Gibb
Barry
B
Storm
Johan F
JF
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D000242:Cyclic AMP / Q000235:genetics / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D054815:Cyclic Nucleotide-Gated Cation Channels; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology; D007473:Ion Channels / Q000235:genetics / Q000502:physiology; D007700:Kinetics; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010782:Photolysis; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D017966:Pyramidal Cells / Q000502:physiology; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D013997:Time Factors; D014982:Xenopus laevis
D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D024681:Potassium Channels, Calcium-Activated; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases