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Raphael C Lee

Publications and source records attributed to Raphael C Lee.

23 records · Page 2Linked to original sources
PubMed2002

Resealing dynamics of a cell membrane after electroporation.

The membrane of a living cell consists of a bilayer of amphipolar lipid molecules as well as much larger proteins. Transmembrane potentials of up to 120 mV are physiologic and well tolerated, but when the potential is more than 300 mV, this lipid bilayer is unstable. Pores are then formed through which measurable flow of ions can occur. We follow currents through frog muscle cell membranes under 4-ms pulses of up to 440 mV. We present a theory that allows us to describe the relaxation of the current back to zero after the pulse in terms of membrane parameters. We obtain a line tension of 3.6 x 10(-6) N, which is similar to that found in artificial lipid bilayers.

Animals↗
PubMed2002

Direct observation of poloxamer 188 insertion into lipid monolayers.

P188, a triblock copolymer of the form poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) helps seal electroporated cell membranes, arresting the leakage of intracellular materials from the damaged cells. To explore the nature of the interaction between P188 and cell membranes, we have constructed a model system that assesses the ability of P188 to insert into lipid monolayers. Using concurrent Langmuir isotherm and fluorescence microscopy measurements, we find that P188 changes the phase behavior and morphology of the monolayers. P188 inserts into both dipalmitoylphosphatidlycholine and dipalmitoylphosphatidylglycerol monolayers at surface pressures equal to and lower than approximately 22 mN/m at 30 degrees C; this pressure corresponds to the maximal surface pressure attained by P188 on a pure water subphase. Similar results for the two phospholipids indicate that P188 insertion is not influenced by headgroup electrostatics. Because the equivalent surface pressure of a normal bilayer is on the order of 30 mN/m, the lack of P188 insertion above 22 mN/m further suggests the poloxamer selectively adsorbs into damaged portions of electroporated membranes, thereby localizing its effect. P188 is also found to be "squeezed out" of the monolayers at high surface pressures, suggesting a mechanism for the cell to be rid of the poloxamer when the membrane is restored.

Cell Membrane↗
PubMed2002

Blood extraction from lancet wounds using vacuum combined with skin stretching.

Key factors and practical limits of blood extraction from lancet wounds on body sites other than the finger were determined by testing a large number of conditions. During these tests, the pain associated with lancing alternate body sites was rated as less painful than a fingerstick 98% of the time. Vacuum combined with skin stretching was effective in extracting an adequate volume of blood from the forearm for glucose testing, up to an average of 16 microl in 30 s. The amount of blood extracted increases with the application of heat or vacuum before lancing, the level of vacuum, the depth of lancing, the time of collection, and the amount of skin stretching. Vacuum and skin stretching led to significant increases, up to fivefold in the perfusion of blood in the skin as measured by laser Doppler. Our observations suggest that vacuum combined with skin stretching increases blood extraction at alternate sites by increasing the lancet wound opening, increasing the blood available for extraction by vasodilatation, and reducing the venous return of blood through capillaries.

Blood Specimen Collection↗