Insulin effect on translational diffusion of lipids and proteins in the plasma membrane of isolated rat hepatocytes

Abstract

The effects of insulin ( 10 −10−10 −8 mol/l ) on lateral diffusion of three fluorescent lipid probes, 1- acyl-2-(N-4- nitrobenzo-2- oxa-1,3- diazole)aminocaproyl phosphatidylcholine (NBD-PC), 5-(N- hexadecanoyl)aminofluorescein (F-C16), 5-(N- dodecanoyl)aminofluorescein (F-C12), and of fluorescein isothiocyanatelabeled proteins in the plasma membrane of intact rat hepatocytes were studied by the technique of fluorescence recovery after photobleaching. The absolute lateral diffusion coefficients of the lipid analogues NBD-PC, F-C16 and F-C12 at 21°C were 2.5 · 10 −9 cm 2/s, 5.4 · 10 −9 cm 2/s and 19 · 10 −9 cm 2/s, respectively. The diffusion coefficient mean of proteins labeled with fluorescein isothiocyanate was 6.4 · 10 −10 cm 2/s. Insulin at 10 −9 and 10 −8 mol/l reduced the lateral diffusion coefficient for F-C12- and F-C16-labeled cells by 20% and for NBD-PC-labeled cells by 30% ( P < 0.025). The insulin effect was specific as tested by cell incubation with proinsulin and desoctapeptide insulin (10 −8 mol/l) and was detectable after 7 min of insulin preincubation. In contrast to lateral diffusion of lipid probes, lateral mobility of unselected membrane proteins was not altered by insulin. The observed modulation of lipid dynamics in the plasma membrane of intact hepatocytes, by which a variety of membrane functions can be influenced, may be an important step in the mechanism of insulin action.