Vol. 32, Nos. 2-3 Free Communications 299 equations for the red blood cell, without any linearity assumptions. In order to develop a "microscopic" constitutive relation, we considered for the various parts of the red blood cell specific perturbations of the forms of the existing and above mentioned constitutive relations. In other words, we considered "small" proper deviations of the above stated forms as microscopic constitutive relations clearly taking into account the practical results. In this way, sets of non-linear equations have been obtained, each one separately corresponding to the classes of the considered constitutive relations. The aforementioned sets of non-linear equations have been solved by means of the finite element method for the non-linear systems, applied in high performance computers. Finally, an extensive comparative study of the various forms of microscopic constitutive relations with the actual experimental data has been performed. Therefore, the most promising microscopic constitutive relation is proposed. F140. MICROPIPETTE INDUCED ECHINOCYTES--A RESULT OF TRANSBIIAYER LIPID TRANSLOCATIONS G. ARTMANN, K-L. P. SUNGt, T. H. HORNS, D. WHITTEMOREt, AND S. CHIENt Department Applied Cell Biophysics, FH Aachen, D-52428 Jiilich, Germany #Institute for Biomedical Engineering, University of California at San Diego, LaJolla, CA 92037, USA SNeuropharmacolgy, Scripps Research Institute, LaJolla, CA 92037, USA In experiments where discocytic erythrocytes (RBCs) were first aspirated into glass pipettes (pipette inner radius of Rp=0.5 ~tm) with a negative aspiration pressure (Pp=5 kPa) and then released after holding the pressure constant for 10 to 300-seconds (holding time, th), the RBC underwent a shape transformation from a discocyte to an echinocyte (temperature T=22 ° C, phosphate buffered saline, PBS, with 0.25% bovine serum albumin)). The shape transformation was more pronounced after a longer th at a constant aspiration pressure. Using Pp=4.9 kPa, th=10 seconds and Rp=0.65 Mm, the treated RBC became an ecfiinocyte-II, whereas a spheroechinocyte-I was observed with th=65 seconds The echinocytic shape recovered to the discocytic shape spontaneously and completely within 14 minutes 23 seconds and within 33 minutes 42 seconds for th=65 seconds The pipette-induced echinocytic RBC shape was also observed in PBS containing 200 I.tM sodium orthovanadate (Na304V ' (SOV)). The echinocytic shape did not recover to the discocytic shape in PBS containing SOV but did recover in PBS alone. Thus, SOV inhibited the pipette induced shape recovery. Chlorpromazine (CP), a stomatocytic substance, reversed the pipette-induced echinocytic shape (Pp=3.9 kPa, th--10 seconds and Rp=0.55 ~tm) within less than 2 minutes after exposing file echinocyte with 25 ~tM CP. After another 30 minutes, this discocyte became a sphero stomatocyte-II. We explain the basic mechanism of the pipette induced echinocytosis as follows: During the aspiration of RBC membrane into the pipette using a very high pressure, an isotropic tension was induced within the RBC membrane and the cytosolic pressure inside the aspirated RBC increased. This was followed by an outflow of cytosolic water. This caused lipids from the inner leaflet of the membrane to flop to the outer leaflet. After the sudden release of membrane tension by releasing the RBC from the pipette, the tension and the cytosolic water content normalized