Modulation of the Ca2+-activated K+ current sIAHP by a phosphatase-kinase balance under basal conditions in rat CA1 pyramidal neurons.
The slow Ca2+-activated K+ current, sIAHP, underlying spike frequency adaptation, was recorded with the whole cell patch-clamp technique in CA1 pyramidal neurons in rat hippocampal slices. Inhibitors of serine/threonine protein phosphatases (microcystin, calyculin A, cantharidic acid) caused a gradual decrease of sIAHP amplitude, suggesting the presence of a basal phosphorylation-dephosphorylation turnover regulating sIAHP. Because selective calcineurin (PP-2B) inhibitors did not affect the amplitude of sIAHP, protein phosphatase 1 (PP-1) or 2A (PP-2A) are most likely involved in the basal regulation of this current. The ATP analogue, ATP-gamma-S, caused a gradual decrease in the sIAHP amplitude, supporting a role of protein phosphorylation in the basal modulation of sIAHP. When the protein kinase A (PKA) inhibitor adenosine-3', 5'-monophosphorothioate, Rp-isomer (Rp-cAMPS) was coapplied with the phosphatase inhibitor microcystin, it prevented the decrease in the sIAHP amplitude that was observed when microcystin alone was applied. Furthermore, inhibition of PKA by Rp-cAMPS led to an increase in the sIAHP amplitude. Finally, an adenylyl cyclase inhibitor (SQ22, 536) and adenosine 3',5'-cyclic monophosphate-specific type IV phosphodiesterase inhibitors (Ro 20-1724 and rolipram) led to an increase or a decrease in the sIAHP amplitude, respectively. These findings suggest that a balance between basally active PKA and a phosphatase (PP-1 or PP-2A) is responsible for the tonic modulation of sIAHP, resulting in a continuous modulation of excitability and firing properties of hippocampal pyramidal neurons.
Pedarzani
P
P
Department of Molecular Biology of Neuronal Signals, Max-Planck-Institute for Experimental Medicine,37075 Gottingen, Germany.
Krause
M
M
Haug
T
T
Storm
J F
JF
Stühmer
W
W
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000201:enzymology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D015221:Potassium Channels / Q000502:physiology*; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D054645:Protein Phosphatase 1; D017966:Pyramidal Cells / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D004791:Enzyme Inhibitors; D015221:Potassium Channels; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D000262:Adenylyl Cyclases; D002118:Calcium