Studies on the lack of cooperativity in the melting of lipid bilayers

The gel-to-fluid first-order melting transition of lipid bilayers is simulated by the use of a microscopic interaction model which includes a variable number of lipid-chain conformational states. The results suggest that the experimental observation of ‘continuous melting’ in pure wet lipid bilayers, rather than being ascribed to the presence of impurities, may be explained as a result of kinetically caused metastability of intermediate lipid-chain conformations.     

Na+, Cl− cotransport in Ehrlich ascites tumor cells activated during volume regulation (regulatory volume increase)

Ehrlich ascites cells were preincubated in hypotonic medium with subsequent restoration of tonicity. After the initial osmotic shrinkage the cells recovered their volume within 5 min with an associated KCl uptake. The volume recovery was inhibited when NO-3 was substituted for Cl-, and when Na+ was replaced by K+, or by choline (at 5 mM external K+). The volume recovery was strongly inhibited by furosemide and bumetanide, but essentially unaffected by DIDS. The net uptake of Cl- was much larger than the value predicted from the conductive Cl- permeability. The undirectional 36Cl flux, which was insensitive to bumetanide under steady-state conditions, was substantially increased during regulatory volume increase, and showed a large bumetanide-sensitive component. During volume recovery the Cl- flux ratio (influx/efflux) for the bumetanide-sensitive component was estimated at 1.85, compatible with a coupled uptake of Na+ and Cl-, or with an uptake via a K+,Na+,2Cl- cotransport system. The latter possibility is unlikely, however, because a net uptake of KCl was found even at low external K+, and because no K+ uptake was found in ouabain-poisoned cells. In the presence of ouabain a bumetanide-sensitive uptake during volume recovery of Na+ and Cl- in nearly equimolar amounts was demonstrated. It is proposed that the primary process during the regulatory volume increase is an activation of an otherwise quiescent, bumetanide-sensitive Na+,Cl- cotransport system with subsequent replacement of Na+ by K+ via the Na+/K+ pump, stimulated by the Na+ influx through the Na+,Cl- cotransport system.     

Migration Inhibition Studies on Peripheral Leukocytes and Lymph Node Cells from Ruminants with Fascioliasis

Delayed type hypersensitivity against antigens of Fasciola hepatica has been repeatedly documented in infected hosts. Evidence has been presented to suggest that the delayed reactivity may develop earlier in the regional lymph nodes of the parasitized organ than in other lymph nodes of the body (Soulsby 1971).     

Inositol 1,3,4,5-tetrakisphosphate is essential for sustained activation of the Ca2+-dependent K+ current in single internally perfused mouse lacrimal acinar cells

Summary We have examined the effects of various inositol polyphosphates, alone and in combination, on the Ca²⁺-activated K⁺ current in internally perfused, single mouse lacrimal acinar cells. We used the patch-clamp technique for whole-cell current recording with a set-up allowing exchange of the pipette solution during individual experiments so that control and test periods could be directly compared in individual cells. Inositol 1,4,5-trisphosphate (Ins 1,4,5 P₃) (10–100 m) evoked a transient increase in the Ca²⁺-sensitive K⁺ current that was independent of the presence of Ca²⁺ in the external solution. The transient nature of the Ins 1,4,5 P₃ effect was not due to rapid metabolic breakdown, as similar responses were obtained in the presence of 5mm 2,3-diphosphoglyceric acid, that blocks the hydrolysis of Ins 1,4,5 P₃, as well as with the stable analoguedl-inositol 1,4,5-trisphosphorothioate (Ins 1,4,5 P(S)₃) (100 m). Ins 1,3,4 P₃ (50 m) had no effect, whereas 50 m Ins 2,4,5 P₃ evoked responses similar to those obtained by 10 m Ins 1,4,5 P₃. A sustained increase in Ca²⁺-dependent K⁺ current was only observed when inositol 1,3,4,5-tetrakisphosphate (Ins 1,3,4,5 P₄) (10 m) was added to the Ins 1,4,5 P₃ (10 m)-containing solution and this effect could be terminated by removal of external Ca²⁺. The effect of Ins 1,3,4,5 P₄ was specifically dependent on the presence of Ins 1,4,5 P₃ as it was not found when 10 m concentrations of Ins 1,3,4 P₃ or Ins 2,4,5 P₃ were used. Ins 2,4,5 P₃ (but not Ins 1,3,4 P₃) at the higher concentration of 50 m did, however, support the Ins 1,3,4,5 P₄-evoked sustained current activation. Ins 1,3,4 P₃ could not evoke sustained responses in combination with Ins 1,4,5 P₃ excluding the possibility that the action of Ins 1,3,4,5 P₄ could be mediated by its breakdown product Ins 1,3,4 P₃. Ins 1,3,4,5 P₄ also evoked a sustained response when added to an Ins 1,4,5 P(S)₃-containing solution. Ins 1,3,4,5,6 P₅ (50 m) did not evoke any effect when administered on top of Ins 1,4,5 P₃. In the absence of external Ca²⁺, addition of Ins 1,3,4,5 P₄ to an Ins 1,4,5 P₃-containing internal solution evoked a second transient K⁺ current activation. Readmitting external Ca²⁺ in the continued presence internally of Ins 1,4,5 P₃ and Ins 1,3,4,5 P₄ made the response reappear. We conclude that both Ins 1,4,5 P₃ and Ins 1,3,4,5 P₄ play crucial and specific roles in controlling intracellular Ca²⁺ homeostasis.     

Mitochondrial malate dehydrogenase from watermelon: sequence of cDNA clones and primary structure of the higher-plant precursor protein

The isolation and sequence of a cDNA clone encoding the complete mitochondrial malate dehydrogenase (mMDH) of watermelon cotyledons is presented. Taking advantage of the polymerase chain reaction technology partial cDNA clones from the central part, the 3 part and the 5 part of the mRNA were obtained with oligonucleotides based on directly determined amino acid sequences. Subsequently, two complete cDNA clones for mMDH were synthesized with a sense primer corresponding to the nucleotide sequence of the amino terminal end of pre-mMDH and two antisense primers corresponding to the major alternative adenylation sites found in the mRNA.The amino acid residues for substrate and cofactor binding identified by X-ray crystallography for pig heart cytoplasmic MDH are conserved in the 320 amino acid long mature higher-plant mMDH. A presequence of 27 amino acids is present at the amino terminal end of the precursor protein.     

Oxygen transport in the blood of arctic mammals: adaptation to local heterothermia

Summary The oxygen binding of whole blood from humans and two arctic mammals, reindeer and muskox, has been studied as a function of carbon dioxide and temperature. All bloods display a marked Bohr effect with Bohr coefficients in the range –0.44––0.73. The Bohr effect is more pronounced at 20°C. The temperature sensitivity of reindeer and muskox blood expressed by the apparent heat of oxygenation, H, is almost three times lower than that of human HbA under the same experimental conditions. This thermodynamic difference gives special benefits to arctic mammals with large heterothermy by safeguarding oxygen unloading at very low ambient temperatures.     

Properties of plasma low density lipoproteins in patients with hypertriglyceridemia and ischemic heart disease

It has been shown that low-density plasma lipoproteins in patients with ischemic heart disease and hypertriglyceridemia are heavier in density, smaller in size, more negatively charged and more inclined to peroxide modification and aggregation than in healthy persons. The protein in the composition of such lipoproteins deviates towards the water phase, which may result in the masking of the domen, recognized by the BE-receptor and may lead to hyperlipidemia of a retaining character.