Cyclosporine A induces an early and transient rigidification of lymphocyte membranes

The effect of cyclosporine A (CsA) on peripheral blood lymphocyte (PBL) membranes was studied using fluorescence techniques. Light scattering and intercalation experiments indicate CsA has a critical micelle concentration of 3 x 10(-5) M. Doses above this critical concentration were avoided during these in vitro studies. Steady-state fluorescence polarization of the lipid probe DPH in peripheral blood lymphocyte membranes revealed that 10(-5) M CsA caused a significant increase in the fluorescence polarization 1-5 min after exposure (15-16% above control DPH polarization values). This initial increase in polarization plateaued at 10-11% above control values within roughly 40 min. Fluorescence lifetime measurements of DPH during this response reveal a slight increase in DPH lifetime. The increased DPH lifetimes showed that polarization measurements alone underestimate the rigidity of DPH's microenvironment. Measurements of DPH polarization and lifetime were analyzed using the Perrin equation to calculate the apparent microviscosity. Control PBL membranes at 37 degrees C exhibited a microviscosity (eta) equal to 1.89 poise (P). Five to 10 min after CsA exposure eta = 2.62-2.68 P and plateaus at eta = 2.31-2.51 P 20-120 min after exposure. Dose-response studies show that prolonged (greater than 90 min) exposure to CsA alters lymphocyte membrane fluidity. This early response in lymphocytes to CsA may correspond to other events associated with the initial binding of CsA to lymphocyte membranes such as membrane depolarization and alterations in phospholipid metabolism. Intravenous delivery of CsA in clinical studies has shown that a similar CsA dose of near 10(-5) M is available in the blood during the first hour after injection. The evidence presented here suggests that peripheral blood lymphocyte membranes are rigidified when exposed to CsA doses similar to those found in patient's blood immediately following intravenous administration.