Inwardly rectifying K+ currents in fetal alveolar type II cells: regulation by protein kinase A and protein phosphatases.
Fetal guinea-pig lung alveolar type II (ATII) cells have inwardly rectifying (IR) K+ currents that display Mg2+- and G-protein-dependent run-down. We have used the whole-cell patch-clamp technique to investigate further the regulation of these currents. Under control conditions [KCl-rich pipette solution (1 mM free Mg2+, 10 nM free Ca2+) and KCl-rich bath solution], we found that IR K+ currents diminished with a t1/2 of 7.6 min and were absent by 30 min. Experimental manoeuvres designed to inhibit phosphorylation increased the rate of current run-down. Thus, intracellular addition of 100 microM H-7, a general kinase inhibitor, reduced the t1/2 to 4.7 min and the currents were absent by 16 min. Similarly, protein kinase A (PKA) inhibitor peptide (50 nM) also accelerated run-down. Agents known to increase phosphorylation, such as db-cAMP (0.5 mM) and forskolin (10 microM), resulted in a significant slowing of run-down (t1/2>16 min) as did intracellular addition of the catalytic subunit of PKA (100 nM). Similarly, inhibition of dephosphorylation by either 1 microM okadaic acid [protein phosphatase 1/2A (PP-1/2A) inhibitor] or anti-human protein phosphatase 2Calpha (PP2C) antiserum decreased the rate of run-down. These results indicate that the phosphorylation-dependent activation state of the fetal ATII cell IR K+ channel is regulated by a complex interplay of kinases and phosphatases involving PKA (activation), and PP2C and PP-1/2A (inactivation).
Lung Membrane Transport Group, Tayside Institute of Child Health, Ninewells Hospital and Medical School, University of Dundee Dundee DD1 9SY, UK.
A S
AS
Monaghan
D L
DL
Baines
R
R
Muimo
R E
RE
Olver
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004553:Electric Conductivity; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D018408:Patch-Clamp Techniques; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology*; D011247:Pregnancy; D047428:Protein Kinase Inhibitors; D054645:Protein Phosphatase 1; D011650:Pulmonary Alveoli / Q000166:cytology / Q000196:embryology / Q000502:physiology*
D004791:Enzyme Inhibitors; D015221:Potassium Channels; D047428:Protein Kinase Inhibitors; D005576:Colforsin; D003994:Bucladesine; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1