Enhancement of recombinant gamma-aminobutyric acid type A receptor currents by chronic activation of cAMP-dependent protein kinase.
alpha 1, beta 1, and gamma 2S gamma-aminobutyric acid (GABA) type A receptor (GABAR) subunit cDNAs were transiently expressed in derivative cell lines of mouse L929 fibroblasts, which possessed different levels of the catalytic subunit of cAMP-dependent protein kinase (PKA). These cell lines included L929 (intermediate levels of kinase), C alpha 12 (elevated levels of kinase), and RAB10 (low levels of kinase) cells. Pharmacological analysis of GABA-evoked whole-cell currents revealed that, compared with expression in L929 and RAB10 cells, expression of alpha 1 beta 1 gamma 2S GABARs in C alpha 12 cells produced a selective enhancement of single whole-cell current amplitudes. No other pharmacological properties (Hill slope, EC50, or diazepam sensitivity) of the expressed alpha 1 beta 1 gamma 2S GABARs were modified. The GABAR current enhancement in C alpha 12 cells was blocked by substitution of a beta 1 subunit mutated at the PKA consensus phosphorylation site, Ser409 [beta 1(S409A)], for the wild-type beta subunit. Interestingly, enhancement was specific for GABARs containing all three subunits, because it was not seen after expression of alpha 1 beta 1 or alpha 1 beta 1 (S409A) GABAR subunit combinations. Single-channel conductance and gating properties were not different for alpha 1 beta 1 gamma 2S or alpha 1 beta 1 (S409A) gamma 2S GABARs expressed in each cell line, suggesting that PKA did not enhance whole-cell currents by altering these properties of GABARs. These results suggested that unlike acute application of PKA, which has been shown to produce a decrease in GABAR current, chronic elevation of PKA activity can result in enhancement of GABAR currents. More importantly, this effect occurred only with GABARs composed of alpha 1 beta 1 gamma 2S subunits and not alpha 1 beta 1 subunits and was mediated by a single amino acid residue (Ser409) of the beta 1 subunit.
Angelotti
T P
TP
Department of Pharmacology, University of Michigan Medical School, Ann Arbor 48109.
Uhler
M D
MD
Macdonald
R L
RL
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004789:Enzyme Activation; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D009838:Oligodeoxyribonucleotides; D011494:Protein Kinases / Q000378:metabolism*; D018079:Receptors, GABA / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism
D009838:Oligodeoxyribonucleotides; D018079:Receptors, GABA; D011994:Recombinant Proteins; D011494:Protein Kinases