Abstract
The effect of palmitic acid (PA) and oleic acid (OA) on electrical parameters of planar membranes was studied. We found a substantial difference between the effects of PA and OA 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 (49 x 10(-6) s(-1)) anions. Cholesterol, included in the membrane-forming solution, decreased importantly the leak conductance both in membranes unmodified by FA and in membranes modified by PA added to the bath.
Highlights
The effect of palmitic acid (PA) and oleic acid (OA) on electrical parameters of planar membranes was studied
Soybean l-␣-phosphatidylcholine, PA, oleic acid (OA), and Tris were obtained from Sigma
The corresponding short circuit (SCC) directed from the cis to the trans side was found to be typically in the few picoampere range (Table 1)
Summary
Soybean l-␣-phosphatidylcholine (asolectin), PA, oleic acid (OA), and Tris were obtained from Sigma Bathing solutions were symmetric at the time of membrane formation (5 mM KCl, 5 mM KH2PO4, and 5 mM Tris, pH 7.4). Sulfuric acid was added to the cis side to create a pH difference (⌬pH) across the membrane (from 0.4 to 2.0 pH units). Aliquots of PA or OA (ethanolic solutions) were added to both cis and trans sides at a final aqueous concentration of 40–65 M. The membrane open-circuit voltage (Em), membrane conductance (Gm), and membrane resistance (Rm) are derived from the elements of Fig. 1A and given (Fig. 1B) by equation 2:. ---1---Gm where GH is the proton conductance and Gleak is the leak conductance
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