Effect of insulin on the lytic action of lysophosphatidylcholine in lipid bilayers

An overview of Argentine contributions to diabetes research in the decade of the 1990s

Argentina has a longstanding tradition of diabetes research, beginning with the seminal work of Prof. Bernardo A. Houssay, who was awarded the first Nobel Prize in Medical Sciences for his studies on the relationship between diabetes and pituitary function. Prof. Luis F. Leloir, who was also awarded the Nobel Prize for his work in carbohydrate metabolism, also inspired younger generations of biologists to work in the field of diabetes research. The aim of this paper is to provide a review of the contributions of Argentine researchers during the 1990s. This manuscript includes only reports of Argentine researchers working on diabetes in local laboratories and quoted in Medline. Thus, important contributions not reported in journals included in Medline or produced by Argentine researchers working abroad may have been omitted. The material consists of a brief description of clinical research (epidemiology and costs, metabolic control, associated risk factors, immunological aspects, and other clinical studies) and basic research (animal model with spontaneous diabetes, islet morphology and function in normal and pathological conditions, insulin action, metabolic disorders related to diabetes, and some miscellaneous effects related to drug-induced diabetes). Altogether, a broad idea of the continuous contribution of our national research to the international field of diabetes is provided, as well as a list of Argentine researchers and research centers devoted to the study of diabetes.

Surface changes induced by osmotic shrinkage on large unilamellar vesicles

Osmotic shrinkage changes the surface properties of dipalmitoylphosphatidylcholine large unilamellar vesicles depending on the phase state of the bilayer. In the gel state, shrinkage produces an increase in the adsorption of hydrophobic dyes, such as Merocyanine 540 (MC540) monomers, toluidine and anilinonaphthalene sulfonic acid (TNS, ANS). In the fluid state, shrinkage does not affect the bilayer surface when gradients between the inner and the outer compartments below 0.2-0.25 M NaCl (higher concentration outside) are applied. Larger differences in concentrations produce an increase in packing as inferred from the desorption of the MC monomers. Kinetic experiments show that the surface changes correlate with the volume decrease produced by the water extrusion from the vesicle interior. It is interpreted that the decrease of water content compels the vesicles to a state in which defects at the membrane surface are likely to occur when the bilayer is in the gel state.

Substrate level modulation of the activity of phospholipase A2 in vitro by 12-O-tetradecanoylphorbol-13-acetate

The action of porcine pancreatic phospholipase A2 towards fluorescent phospholipid analogs is either enhanced or suppressed by 4 beta-12-O-tetradecanoylphorbol-13- acetate (TPA), depending on the chemical structure of the substrate and the concentration of Ca2+. In the presence of nmolar Ca2+ concentrations increasing [TPA] enhanced by approx. 5-fold the rate of hydrolysis of the pyrene-labelled acidic alkyl-acyl phospholipid, 1-octacosanyl-2-[6- (pyrene-1-yl)] hexanoyl-sn-glycero-3-phosphatidylmethanol. Maximal effect was obtained at high TPA/substrate molar ratios approaching 1:2. In the presence of 4 mM CaCl2 maximal activation was reduced to approximately 1.5-fold. With the corresponding phosphatidylcholine derivative as a substrate increasing [TPA] reduced fatty acid release maximally by 90% both at low [Ca2+] as well as in the presence of 4 mM CaCl2. Essentially identical results were obtained using 4 alpha-TPA, a stereoisomer which does not activate protein kinase C.

The local anesthetic tetracaine destabilizes membrane structure by interaction with polar headgroups of phospholipids

The effect of the local anesthetic tetracaine at less than 10 mM on the water permeability of the phospholipid membrane was examined using liposomes composed of various molar ratios of negatively charged cardiolipin to electrically neutral phosphatidylcholine by monitoring their osmotic shrinkage in hypertonic glucose solution at 30 degrees C. The concentration of tetracaine causing the maximum velocity of shrinkage of liposomes increased with increase in the molar ratio of cardiolipin. Tetracaine increased the zeta-potential of the negatively charged liposomal membrane toward the positive side due to the binding of its cationic form to the negatively charged polar headgroups in the membrane. The maximum velocity of water permeation induced by osmotic shock was observed at essentially the same tetracaine concentration giving a zeta-potential of the liposomal membrane of 0 mV. These concentrations were not affected by change in the sort of acyl-chain of phospholipids in the liposomes when their negative charges were the same. These results suggests that the membrane integrity is governed mainly by the electrical charge of phospholipid polar headgroups when phospholipid bilayers are in the highly fluid state, and that positively charged tetracaine molecules neutralize the negative surface charge, lowering the barrier for water permeation through phospholipid bilayers.