{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Niles88 - PLANAR BILAYER MEMBRANES MADE FROM PHOSPHOLIPID...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
PLANAR BILAYER MEMBRANES MADE FROM PHOSPHOLIPID MONOLAYERS FORM BY A THINNING PROCESS WALTER D. NILES, RICHARD A. LEVIS, AND FREDRIC S. COHEN Rush Medical College, Department of Physiology, Chicago, Illinois 60612 ABSTRACT We investigated the manner in which planar phospholipid membranes form when monolayers are sequentially raised. Simultaneous electrical and optical recordings showed that initially a thick film forms, and the capacitance of the film increases with the same time course as the observed thinning. The diameter of fully thinned membranes varies from membrane to membrane and a torus is readily observed. The frequency-dependent admittance of the membrane was measured using a wide-bandwidth voltage clamp whose frequency response is essentially independent of capacitative load. The membrane capacitance dominates the total admittance and the membrane dielectric is not lossy. The specific capacitance of membranes of several mixtures was measured. A schematic diagram of the formation of these membranes is presented. INTRODUCTION There are two basic methods for forming phospholipid bilayer membranes. In the first, lipid is dissolved in a nonvolatile hydrocarbon solvent. A small quantity of this membrane-forming solution is applied to a hole in a sheet, typically made of Teflon, separating two aqueous compart- ments. The hydrocarbon drains into a Gibbs-Plateau bor- der (known as a torus), which surrounds the thin film that forms (Mueller et al., 1963). This thin film, referred to as a black lipid membrane (BLM), consists of a phospholipid bilayer with a considerable amount of dissolved solvent (Hanai et al., 1965; White, 1972). In the second method, bilayers are formed from monolayers as originally described by Takagi et al. (1965) and modified by Montal and Mueller (1972). Monolayers spread at two air-water interfaces are sequentially raised over a hole that has been pretreated with hydrocarbons such as Vaseline or squalene (Montal, 1974; Reyes and Latorre, 1979), and a phospho- lipid bilayer forms where the monolayers meet. These latter membranes, which we refer to as MM films, are relatively solvent-free. They are commonly described as forming via the direct apposition of the two monolayers (Montal, 1974; White et al., 1976). Here we report simultaneous optical and electrical studies showing that contrary to the common view, sequen- tial raising of the monolayers results initially in the forma- tion of a thick hydrocarbon-phospholipid mixture within the hole. Only when the hydrocarbon drains does a bilayer form. When the membrane has fully thinned, a visually apparent torus surrounds the bilayer. By measuring the area of thinned MM membranes and using a specially constructed wide-bandwidth voltage clamp, we measured the specific capacitance of the bilayer.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}