Activation and deactivation kinetics of alpha 2A- and alpha 2C-adrenergic receptor-activated G protein-activated inwardly rectifying K+ channel currents.
Although G protein-coupled receptor-mediated signaling is one of the best studied biological events, little is known about the kinetics of these processes in intact cells. Experiments with neurons from alpha(2A)-adrenergic receptor knockout mice suggested that the alpha(2A)-receptor subtype inhibits neurotransmitter release with higher speed and at higher action potential frequencies than the alpha(2C)-adrenergic receptor. Here we investigated whether these functional differences between presynaptic alpha(2)-adrenergic receptor subtypes are the result of distinct signal transduction kinetics of these two receptors and their coupling to G proteins. alpha(2A)- and alpha(2C)-receptors were stably expressed in HEK293 cells at moderate ( approximately 2 pmol/mg) or high (17-24 pmol/mg) levels. Activation of G protein-activated inwardly rectifying K(+) (GIRK) channels was similar in extent and kinetics for alpha(2A)- and alpha(2C)-receptors at both expression levels. However, the two receptors differed significantly in their deactivation kinetics after removal of the agonist norepinephrine. alpha(2C)-Receptor-activated GIRK currents returned much more slowly to base line than did alpha(2A)-stimulated currents. This observation correlated with a higher affinity of norepinephrine at the murine alpha(2C)- than at the alpha(2A)-receptor subtype and may explain why alpha(2C)-adrenergic receptors are especially suited to control sympathetic neurotransmission at low action potential frequencies in contrast to the alpha(2A)-receptor subtype.
Bünemann
M
M
Institut für Pharmakologie und Toxikologie, Universität Würzburg, Versbacher Strasse 9, 97078 Würzburg, Germany.
Bücheler
M M
MM
Philipp
M
M
Lohse
M J
MJ
Hein
L
L
D000200:Action Potentials; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D004789:Enzyme Activation; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D009638:Norepinephrine / Q000378:metabolism / Q000494:pharmacology; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying; D011485:Protein Binding; D011869:Radioligand Assay; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000737:chemistry* / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
C547768:ADRA2A protein, human; C547774:ADRA2C protein, human; C547769:Adra2a protein, mouse; C547775:Adra2c protein, mouse; D015220:Calcium Channels; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011942:Receptors, Adrenergic, alpha; D018341:Receptors, Adrenergic, alpha-2; D019204:GTP-Binding Proteins; D009638:Norepinephrine