Dc. Devor et Ra. Frizzell, MODULATION OF K-ACID IN T84 CELLS - II - ACTIVATION OF A CA2+-INDEPENDENT K+ CHANNEL( CHANNELS BY ARACHIDONIC), American journal of physiology. Cell physiology, 43(1), 1998, pp. 149-160
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.