TRANSPORT OF K-MEMBRANES BY NONESTERIFIED FATTY-ACIDS( AND OTHER CATIONS ACROSS PHOSPHOLIPID)

The rate of change of internal pH and transmembrane potential has been monitored in liposomes following the external addition of various cat ion salts. Oleic acid increases the transmembrane movement of H+ follo wing the imposition of a K+ gradient. An initial fast change in intern al pH is seen followed by a slower rate of alkalinization. High concen trations of the fatty acid enhance the rate comparable to that seen in the presence of nigericin in contrast to the effect of FCCP (carbonyl cyanide p-(tri-fluoromethoxy)phenyl hydrazone) which saturates at an intermediate value. The ability of nonesterified fatty acids to cataly ze the movement of cations across the liposome membrane increases with the degree of unsaturation and decreases with increasing chain length . Li and Na salts cause a similar initial fast pH change but have less effect on the subsequent slower rate. Similarly, the main effect of d ivalent cation salts is on the initial fast change. The membrane poten tial can enhance or inhibit cation transport depending on its polarity with respect to the cation gradient. It is concluded that nonesterifi ed fatty acids have the capability to complex with, and transport, a v ariety of cations across phospholipid bilayers. However, they do not a ct simply as proton/cation exchangers analogous to nigericin nor as pr otonophores analogous to FCCP. The full cycle of ionophoric action inv olves a combination of bath functions.