Modulation of K1 channels by arachidonic acid in T84 cells. II. Activation of a Ca21-independent K1 channel

Devor, Daniel C., and Raymond A. Frizzell. Modulation of K1 channels by arachidonic acid in T84 cells. II. Activation of a Ca21-independent K1 channel. Am. J. Physiol. 274 (Cell Physiol. 43): C149–C160, 1998.—We used singlechannel recording techniques to identify and characterize a large-conductance, Ca21-independent K1 channel in the colonic secretory cell line T84. In symmetric potassium gluconate, this channel had a linear current-voltage relationship with a single-channel conductance of 161 pS. Channel open probability (Po) was increased at depolarizing potentials. Partial substitution of bath K1 with Na1 indicated a permeability ratio of K1 to Na1 of 25:1. Channel Po was reduced by extracellular Ba21. Event-duration analysis suggested a linear kinetic model for channel gating having a single open state and three closed states: C3;=C2;=C1;=O. Arachidonic acid (AA) increased the Po of the channel, with an apparent stimulatory constant (Ks) of 1.39 μM. Neither channel open time (O) nor the fast closed time (C1) was affected by AA. In contrast, AA dramatically reduced mean closed time by decreasing both C3 and C2. The cis-unsaturated fatty acid linoleate increased Po also, whereas the saturated fatty acid myristate and the trans-unsaturated fatty acid elaidate did not affect Po. This channel is activated also by negative pressure applied to the pipette during inside-out recording. Thus we determined the effect of the stretch-activated channel blockers amiloride and Gd31 on the K1 channel after activation by AA. Amiloride (2 mM) on the extracellular side reduced single-channel amplitude in a voltage-dependent manner, whereas Gd31 (100 μM) had no effect on channel activity. Activation of this K1 channel may be important during stimulation of Cl2 secretion by agonists that use AA as a second messenger (e.g., vasoactive intestinal polypeptide, adenosine) or during the volume regulatory response to cell swelling.