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 activ ated human T cells, Single channel events were recorded using the patc h-clamp technique in cell-attached-patch configuration, The channel wa s K selective, as determined by reversal potentials under different K gradients, and displayed voltage-independent gating, When the applied potential (V-p) was equal to zero, the conductance of the channel was 21.8 +/- 0.9 pS with 150 mM K in the electrode, Typical patches contai ned between two and seven channels that were relatively quiet, or sile nt, before agonist stimulation, Adenosine (20-30 mu M) increased the a verage open time probability from 0.017 +/- 0.008 to 0.108 +/- 0.054 o ver a period of 108 s. Subsequent addition of the phosphodiesterase in hibitor 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, Expon ential 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 .13 +/- 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 k inase A, failed to inhibit adenosine- and Ro 20-1724-induced increases in channel activity, implying a direct action of cAMP on channel gati ng.