Activation by Arachidonic Acid

Mechanosensitive ion channels have been described in many types of cells. These channels are believed to transduce pressure signals into intracellular biochemical and physiological events. In this study, the patch-clamp technique was used to idendfy and characterize a mechanosensitive ion channel in rat atrial cells. In cell-attached patches, negative pressure in the pipette activated an ion channel in a pressure-dependent manner. The pressure to induce half-maximal activation was 12 3 mmHg at +40 mV, and nearly full activation was observed at ~20 mmHg. The probability of opening was voltage dependent, with greater channel activity at depolarized potentials. The mechanosensitive channel was identical to the K + channel previously shown to be activated by arachidonic acid and other lipophilic compounds, as judged by the outwardly rectifying current-voltage relation, single channel amplitude, mean open time (1.4 +-. 0.3 ms), bursty openings, K + selectivity, insensitivity to any known organic inhibitors of ion channels, and pH sensitivity. In symmetrical 140 mM KC1, the slope conductance was 94 -+ 11 pS at +60 mV and 64 8 pS at 6 0 mV. Anions and cations such as CI-, glutamate, Na +, Cs +, Li +, Ca 2+, and Ba 2+ were not permeant. Extracellular Ba ~+ (1 raM) blocked the inward K + current completely. GdCI3 (100 tiM) or CaCI2 (100 wM) did not alter the K + channel activity or amplitude. Lowering of intracellular pH increased the pressure sensitivity of the channel. The K + channel could be activated in the presence of 5 mM intracellular [ATP] or 10 IzM glybenclamide in inside-out patches. In the absence of ATP, when the ATP-sensitive K + channel was active, the mechanosensitire channel could further be activated by pressure, suggesting that they were two separate channels. The ATP-sensitive K + channel was not mechanosensitive. Pressure activated the K + channel in the presence of albumin, a fatty acid binding protein, suggesting that pressure and arachidonic acid activate the K + channel via separate pathways. Address reprint requests to Dr. Donghee Kim, Department of Physiology and Biophysics, Chicago Medical School, 3333 Green Bay Road, North Chicago, IL 60064. J. G~N. PHYSIOL. O The Rockefeller University Press • 0022-1295/92/12/1021/20 $2.00 Volume 100 December 1992 1021-104