Submitted on April 22, 2004
Revised on November 8, 2004
Accepted on November 8, 2004
Fatty acid flip-flop and proton transport determined by short-circuit current in planar bilayers
Kellen Brunaldi, Manoel Arcisio Miranda, Fernando Abdulkader, Rui Curi, and Joaquim Procopio
Physiology and Biophysics, University of Sao Paulo, Sao Paulo 05508-900
Corresponding Author: procopio{at}icb.usp.br
The effect of palmitic and oleic acids on electrical parameters of planar membranes was studied. We found a substantial difference between the effects of palmitic (PA) and oleic (OA) acids on proton transfer. PA induced a small increase in conductance, requiring a new technique for estimating proton-mediated currents across low conductance planar bilayers in which an electrometer is used to measure the transmembrane current under virtual short-circuit (SCC). Open-circuit voltage and SCC were used to determine proton and leak conductances. OA caused a marked increase in membrane conductance, allowing the use of a voltage-clamp technique. From SCC data we were able to estimate the flip-flop rate constants for palmitate (1 x 10-6 s-1) and oleate anions (49 x 10-6 s-1). Cholesterol, included in the membrane forming solution, decreased importantly the leak conductance both in membranes non-modified by FA and in membranes modified by PA added to the bath.