MODULATION OF K-ACID IN T84 CELLS - II - ACTIVATION OF A CA2+-INDEPENDENT K+ CHANNEL( CHANNELS BY ARACHIDONIC)

Modulation of K+ channels by arachidonic acid in T84 cells. II. Activa tion of a Ca2+-independent K+ channel. Am. J. Physiol. 274 (Cell Physi ol. 43): C149-C160, 1998.-We used single-channel recording techniques to identify and characterize a large-conductance, Ca2+-independent Kchannel in the colonic secretory cell line T84. In symmetric potassium gluconate, this channel had a linear current-voltage relationship wit h a single-channel conductance of 161 pS. Channel open probability (P- o) was increased at depolarizing potentials. Partial substitution of b ath K+ with Na+ indicated a permeability ratio of K+ to Na+ of 25:1. C hannel P-o was reduced by extracellular Ba2+. Event-duration analysis suggested a linear kinetic model for channel gating having a single op en state and three closed states: C-3<->C-2<->C-1<->O. Arachidonic aci d (AA) increased the P-o of the channel, with an apparent stimulatory constant (K-s) of 1.39 mu M. Neither channel open time (O) nor the fas t closed time (C-1) was affected by AA. In contrast, AA dramatically r educed mean closed time by decreasing both C-s and C-2. The cis-unsatu rated fatty acid linoleate increased P-o also, whereas the saturated f atty acid myristate and the trans-unsaturated fatty acid elaidate did not affect P-o. This channel is activated also by negative pressure ap plied to the pipette during inside-out recording. Thus we determined t he effect of the stretch-activated channel blockers amiloride and Gd3 on the K+ channel after activation by AA. Amiloride (2 mM) on the ext racellular side reduced single-channel amplitude in a voltage-dependen t manner, whereas Gd3+ (100 mu M) had no effect on channel activity. A ctivation of this K+ channel may be important during stimulation of Cl - secretion by agonists that use AA as a second messenger (e.g., vasoa ctive intestinal polypeptide, adenosine) or during the volume regulato ry response to cell swelling.