ARACHIDONIC-ACID ACTIVATES CATION CHANNELS IN BOVINE ADRENAL CHROMAFFIN CELLS

Microscopic fluorescence analysis of fura-2-loaded bovine adrenal chro maffin cells demonstrates that approximately 70% of the cells responde d to arachidonic acid in increasing the intracellular Ca2+ concentrati on. Because this increase was markedly less in the absence of external Ca2+, we examined the effect of arachidonic acid on Ca2+ influx elect rophysiologically. Bath application of 10 muM arachidonic acid induced a long-lasting inward current when the cell was clamped at -50 mV. Ot her fatty acids, such as oleic acid, linoleic acid, eicosatrienoic aci d, and eicosapentaenoic acid, were all ineffective. The current-voltag e relationships suggest that arachidonic acid may activate voltage-ins ensitive channels. Arachidonic acid (greater-than-or-equal-to 2 muM) a ctivated a single-channel current in the inside-out patch, even in the presence of inhibitors of cyclooxygenase and lipoxygenase, possibly s uggesting that arachidonic acid could activate channels directly. The onset delay of the inward channel current in the outside-out patch con figuration (54.2 +/- 63.5 s; mean +/- SD) was significantly shorter th an that in the inside-out patch one (197.3 +/- 177.7 s). Washout of ar achidonic acid decreased the probability of channel openings in the ou tside-out patch but not in the inside-out one. These results suggest t hat arachidonic acid activates channels reversibly from outside of the plasma membrane. The unitary conductance for Ca2+ of arachidonic acid -activated channel was approximately 17 pS. The arachidonic acid-activ ated channel was permeable to Ba2+, Ca2+, and Na+ but not to Cl-. The opening probability of the arachidonic acid-activated channel did not depend on membrane potential. These results demonstrate that arachidon ic acid activates cation-selective, Ca2+-permeable channels in bovine adrenal chromaffin cells.