We studied the effects of arachidonic acid (AA) on Cl secretion across primary cultures of dog tracheal epithelium. Cell sheets showed mean values for baseline short-circuit current (Isc) and transepithelial resistance of 33.8 μA/cm2 and 360 Ω.cm2 (n=44). AA (5 × 10-5 M) added to both sides increased Isc by 27.8 ±5.2 μA/cm2 (mean±SE, n=8), and elevated intracellular cAMP levels. In the presence of 5 × 10-6 M of both indomethacin (INDO) and nordihydroguaiaretic acid (NDGA) (inhibitors of cyclooxygenase and lipoxygenase, respectively), AA reduced Isc by 4.4 ± 0.6 μA/cm2 (n=10) without changing cAMP. Both INDO and NDGA were necessary to abolish the Isc increase in response to AA. The effects of AA on Isc were unaffected by amiloride. In the presence of INDO and NDGA, isoproterenol (ISO) raised cAMP and increased Isc by 27.6 ± 4.3 (transient) and 12.8 ± 3.2 μA/cm2 (sustained) (n=9). With AA present as well as INDO and NDGA, the transient and sustained responses to ISO were significantly reduced to 13.2 ± 2.4 and 3.9 ± 0.8 μA/cm2 (n=10), respectively; the increase in cAMP was unaltered. AA approximately halved baseline efflux of 125I from confluent cell sheets in high K medium and reduced the isoproterenol-induced increase in efflux to 20% of control. These data are consistent with the reported inhibitory effect of AA on apical membrane chloride channels.
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