Kinetic interaction of fatty acids with outwardly rectifying chloride channels

Outwardly rectifying Cl⁻ channels are present in many tissues and are thought to be defective in Cl⁻-secreting epithelia involved in cystic fibrosis (CF). Polyunsaturated fatty acids in the cis, but not the trans configuration cause rapid intrruptions in the outwardly rectifying Cl⁻ channel currents. In this report, the effects of other physiologically relevant fatty acids were tested. The voltage dependence and the effects of variations in pipette Cl⁻ on the kinetics of the interaction of fatty acids with the channel were explored. Leukotrienes C₄ and D₄ cause rapid interruptions in the single-channel currents with the same potcncy as arachidonic acid and other polyunsaturated fatty acids. The off-rate constant, K_off, evaluated in excised patches in the presence of 30 μM arachidonic acid is voltage dependent at positive voltages, varying ɛ-fold per 68 mV, but voltage independent at negative voltages. In contrast, the on-rate constant, K_on, is voltage independent both at positive and negative voltages. Variations in pipette Cl⁻ between 150 and 300 mV do not affect the voltage dependence of K_off. Similarly, changing pipette [Cl⁻] between 80 and 300 mM does not affect either K_off or K_on. These data suggest that fatty acids do not act as simple, charged, open-channel blockers.