Cyclic adenosine 3',5'-monophosphate increases the open probability of potassium channels in activated human T cells.
In the present report we describe a cAMP-responsive K channel in activated human T cells. Single channel events were recorded using the patch-clamp technique in cell-attached-patch configuration. The channel was K selective, as determined by reversal potentials under different K gradients, and displayed voltage-independent gating. When the applied potential (Vp) was equal to zero, the conductance of the channel was 21.8 +/- 0.9 pS with 150 mM K in the electrode. Typical patches contained between two and seven channels that were relatively quiet, or silent, before agonist stimulation. Adenosine (20-30 microM) increased the average open time probability from 0.017 +/- 0.008 to 0.108 +/- 0.054 over a period of 108 s. Subsequent addition of the phosphodiesterase inhibitor Ro 20-1724 (0.5 mM) increased the probability of being in the open state to 1.155 +/- 0.407 over a period of 180 s. Channel kinetics were well described by assuming two open and two closed states. Exponential time constants for the open states were 0.51 +/- 0.06 and 4.34 +/- 0.31 ms, and closed state time constants were 0.58 +/- 0.05 and 10.1 3 +/- 2.32 ms. In addition, extracellular ATP (0.3-1.0 mM) decreased channel activity. Moreover, Rp-cAMP (0.5-1.0 mM), an antagonist that specifically blocks the ability of cAMP to bind and activate protein kinase A, failed to inhibit adenosine- and Ro 20-1724-induced increases in channel activity, implying a direct action of cAMP on channel gating.
Oleson
D R
DR
Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, GA 30322, USA.
DeFelice
L J
LJ
Quinn
M F
MF
Donahoe
R M
RM
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D018999:Charybdotoxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D004594:Electrophysiology; D006801:Humans; D007700:Kinetics; D008213:Lymphocyte Activation / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism
D015221:Potassium Channels; D018999:Charybdotoxin; D000255:Adenosine Triphosphate; D012964:Sodium; D000242:Cyclic AMP; D011188:Potassium; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine