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The concentration of 5 different proteins in suction blister fluid and serum was determined by immunotechniques. These proteins, varying in size and molecular weight (6,600-2,300,000) were insulin, albumin, high density lipoprotein determined as apoprotein A-I, alpha 2-macroglobulin and low density lipoprotein measured as apoprotein B. The difference in the blister fluid/serum concentration ratio of the proteins was dependent on the molecular weight and followed mainly the law of diffusion. Moreover, the amounts of insulin, albumin and apoproteins A-I and B in suction blister fluid were the same as those reported in peripheral lymph. The results indicate that the sieve function of the capillary basement membrane remains intact during the formation of the suction blisters. Suction blister fluid might therefore be regarded as representative of interstitial fluid. The concentrations of 4 different lipids (cholesterol, cholesterolesters, triglycerides and phospholipids) were also determined and their blister fluid/serum concentration ratio proved to have a fairly constant value of 0.25.

The results obtained m this study show a great influence of the acyl cham on the lyhc behawor of lysoleclthlns and leclthms 1 The lysolectthlns studied, ranged m acyl chain length from 10 to 18 carbon atomsThe palmato)l-and stearoylder~vat~ves were found to be the most active, whereas the shortcham compounds hke decanoyl-lysolectthm showed no activity at allThe possible influence of the glycerohc hydroxylgroup was studied by means of 8 different desoxy-lysoleclthms, '~arymg m chain length from 12 to 26 carbon atoms Thts structural modification, however, turned out to be neghg~ble The highest act~wty was also found for compounds with 16 and 18 carbon atoms, while the shorter and longer chain ones (lauroyl C12, myrlstoyl C14, arach~doyl C20) ~ere less actl~ e, or not achve at all (behenoyl C26, cerotoyl C22)Introduction of double bonds m the acyl chain also rendered the compounds less actwe (oleoyl-I~soleclthm, hnoleoyl-l} solectt hm) 2 Structural varmt~ons m the desox~compounds, hke extension of the alkanedlol skeleton of the molecule or increase of the d~stance between the phosphate group and the quaternary ammomum moiety had ',~rtually no effect 3 It wa~ observed that lecJthlns w~th a chain length |rom 8 to 12 carbon atoms (per acyl chain) are capable of lysmg red cellsThe lecithin with highest activity was found to be dl-undec~loyl-leclthm which was almost as active as the most potent I}solec~thln Shortemng or lengthemng of the acyl chains d~mm~shed the lytlc act~wty, just as m the case of the lysoleclthlns and the desoxy-lvsoleclthlns Therefore at as concluded that lysoleclthms, desoxy-lysoleclthms and lecithms reveal maximum lyt~c activity at a d~stmct chain length 4 It appears that the action ol I~solec~thms, desoxy-lysolec~thms and lec~thms toward red cells and hp~d bfla)ers shows reasonable s~mllarlty ~th the exception of some unsaturated compounds Thts m~ght indicate that the interaction of the lyttc agents w~th the hp~d-constituents of the membrane plays an important role m the process

SUMMARYLight scattering, birefringence and X-ray studies showed that liposomes, with lipid molecules orientated in bilayers, are formed from egg lecithin/lysolecithin mixtures up to 50 mol ~ of lysolecithin; above this concentration much smaller mixed micelles are formed. Permeability studies demonstrated a dramatic increase in the permeability of the liposomes when the lyso concentration exceeds 22.5 mol ~. X-ray studies indicated a significant decrease in bilayer thickness with increasing lysolecithin concentration. It is suggested that decreased interaction energy between the lipid molecules in the bilayer is responsible for the inability of the thin bilayers to act as an effective permeability barrier.Besides diacyl phospholipids, minor quantities of lysophospholipids occur as normal constituents of many biomembranes [1 ]. The lysophospholipids in the membrane are involved in dynamic metabolic processes and the actual concentration seems to be under careful control of various enzyme systems achieving the formation, acylation and breakdown of the lyso compounds [2]. It is generally accepted that the concentration of lyso compounds has important implications for the stability of the interface [3]. Increased lysolecithin concentrations favour conditions for cell fusion [4] and excess of exogenously added lysolecithin causes lysis. Lysis of, for example, red cells has been regarded as primarily an interaction of the lysolecithin molecules with the lipid bilayer in the membrane core. Postulating a "wedge" mechanism for the penetrating lyso molecules, complete break up of the bimolecular leaflet into more or less spherical aggregates of molecules can be considered [3]. On the other hand the lytic process has also been described as being the consequence of more subtle changes in the bilayer orientation causing increase in cation permeability. The disturbance of the Donnan equilibrium then causes entry of water into the cell which bursts by osmotic force [5,6]. Experiments with artificial lipid membranes can be helpful in gaining information on the effects of lysolecithins in biomembranes.Studies on black lipid membranes supported the view that the lyric molecules interfere with the lipid bilayer. In comparative experiments in which lysolecithins or lyric short chain lecithins were added to red cells and to black lipid membranes pre-

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