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R P Rand

Publications and source records attributed to R P Rand.

At least 73 records · Page 4Linked to original sources
PubMed1987

Cryolumpectomy for carcinoma of the breast.

Cryosurgery and surgical en bloc excision in preventing the local recurrence of mammary adenocarcinoma were studied in BALB/cfC3H (supplied by the Cancer Research Institute, University of California Berkeley) syngeneic mice carrying virus induced mammary adenocarcinomas transplanted into the fourth mammary fat pad. Cryosurgical procedures involving multiple freeze-thaw cycles to minus 180 degrees C. followed by tumor excision substantially reduced the local recurrence rate of carcinoma of the mammary gland in the mouse. The use of cryolumpectomy in the treatment of early carcinoma of the breast in humans is presented herein.

Adenocarcinoma↗
PubMed1986

Spontaneous vesicularization of myelin lipids is counteracted by myelin basic protein.

Hand-vortexed dispersions of several lipids (cerebrosides, sulfatides, PC, PE, PS and sphingomyelin), mixed in the ratios found for these categories of lipids in myelin, exhibit 31P-NMR spectra which have contributions from both isotropic and lamellar resonances. Investigation of this system by freeze-fracture electron microscopy and X-ray diffraction revealed that this lipid mixture has spontaneously formed small unilamellar vesicles (SUVs) (diam. approximately 400 A) and large highly convoluted unilamellar vesicles (LUVs) (diam. approximately 1000 A), the latter possibly resulting from aggregation and fusion of the SUV structures. This vesicularization of the myelin lipids was reversed by the addition of myelin basic protein: only large multilamellar aggregates were formed in the presence of protein, as shown by all three experimental methods. Although no rigorous physical-chemical explanation for these phenomena is yet available, the possibility is suggested that the high concentration of cerebrosides and/or phosphatidylethanolamine in this particular mixture of myelin lipids play pivotal roles in the formation of these unusual vesicles. Spontaneous vesicularization of myelin lipids is discussed as a potential pathway toward destabilization of the myelin sheath.

Centrifugation, Density Gradient↗
PubMed1986

Divalent cation induced fusion and lipid lateral segregation in phosphatidylcholine-phosphatidic acid vesicles.

The interactions of unilamellar vesicles containing phosphatidylcholine (PC) and phosphatidic acid (PA) in the presence of calcium and magnesium were examined by fluorometric assays of vesicle lipid mixing, contents mixing, and contents leakage and by spray-freezing freeze-fracture electron microscopy. These results were correlated with calorimetric and fluorometric measurements of divalent cation induced lateral segregation of lipids in these vesicles under comparable conditions. PA-PC vesicles in the presence of calcium show a rapid but limited intermixing of vesicle lipids and contents, the extent of which increases as the vesicle size decreases or the PA content increases. Calcium produces massive aggregation and efficient mixing of the contents of vesicles containing high proportions of dioleoyl-PA or egg PA, but vesicle coalescence in the latter case is followed rapidly by vesicle collapse and massive leakage of contents. The effects of magnesium are similar for vesicles of very high PA content. However, in the presence of magnesium, vesicles containing lower amounts of PA exhibit "hemifusion", a mode of interaction in which vesicles aggregate and mix approximately 50% of their lipids, apparently representing the lipids of the outer monolayer of each vesicle, without significant mixing of vesicle contents or collapse of the vesicles. Fluorometric measurements of lipid lateral segregation demonstrate that lateral redistribution of lipids in PA-PC vesicles begins at submillimolar concentrations of divalent cations and shows no abrupt change at the "threshold" divalent cation concentration, above which coalescence of vesicles is observed. By correlating calorimetric and fluorometric measurements of lipid lateral segregation and mixing of vesicle components, we can demonstrate that lipid segregation is at least strongly correlated with calcium-promoted coalescence of PA-PC vesicles and is essential to the magnesium-promoted interactions of vesicles of low PA contents.

Cations, Divalent↗
PubMed1986

Modification by diacylglycerol of the structure and interaction of various phospholipid bilayer membranes.

The effects of incorporating diacylglycerol (DG) derived from egg phosphatidylcholine (PC) into PC, egg phosphatidylethanolamine (PE), and bovine phosphatidylserine (PS) have been measured. In excess solution DG induces a multilamellar-to-hexagonal (L-H) structural transition in PE and PC that is temperature dependent. At 37 degrees C it begins at about 3 and 30 mol%, respectively. In PC at lower DG concentrations a modified lamellar phase is formed; at about 70 mol% DG a single primitive cubic phase forms. An L-H transition induced by 20-30 mol% DG in PS is dependent on ionic strength and degree of lipid hydration, with the appearance of crystalline acyl chains at the higher DG levels. Calcium precipitates of DG/PS (1/1) mixtures have melted chains. Structural parameters were derived for the lamellar phases at subtransition levels of DG in PE and PC. The area per polar group is increased, but by contrast with cholesterol, the polar group spreading is not accompanied by an increase in bilayer thickness. DG does not affect the equilibrium separation of PC or PE bilayers. Measured interbilayer forces as they vary with bilayer separation show that DG at 20 mol% does not effect closer apposition of PC bilayers at any separation. Spreading the polar groups may effect the binding of protein kinase C or the activation of phospholipases; the nonlamellar phases may be linked to the biochemical production of DG in cellular processes involving membrane fusion.

Animals↗
PubMed1986

Morphological responses to calcium-induced interaction of phosphatidylserine-containing vesicles.

Structural changes in phospholipid vesicles made of dioleylphosphatidylethanolamine (DOPE)/bovine phosphatidylserine (PS) (1/1, 3/1, 10/1) or of egg phosphatidylcholine (PC)/PS (3/1) and exposed to calcium chloride for various times have been observed by means of video-enhanced light microscopy and freeze-fracture electron microscopy. Calcium induces the formation of large, smooth double-bilayer diaphragms as the spherical vesicles adhere to and deform each other. No subsequent changes are seen with PC/PS vesicles. DOPE/PS vesicles respond to the resultant stress, with about equal probability, by either fusing, through diaphragm rupture, or deflating, by way of volume loss through intact bilayers, even when they contain up to 400 mM sucrose. The diaphragm areas only rarely show the structural destabilization necessary for fusion. The final state is lipid segregated into DOPE hexagonal and Ca-PS lamellar bulk phases with the exclusion of most of the vesicle contents. Results with these and pure PS vesicles studied earlier indicate that the early response of vesicles to calcium chloride is determined by the competing rates at which mechanical stress (bilayer tension and intravesicular pressure) builds up as the vesicles adhere and flatten against each other, and is relieved by vesicle fusion or by volume loss. We attribute the qualitatively different responses of these three lipid systems to their measured differences in adhesion energies and consequent rate of build-up of mechanical stress. Yield to that stress for any one of these lipid systems is not a unique sequence of morphological changes, and so it remains obscure how such a stochastic process could be used in the controlled process of cellular fusion.

Animals↗
PubMed1986

Mimicry and mechanism in phospholipid models of membrane fusion.

In spite of heroic efforts, phospholipid bilayer models of fusion do not mimic the cellular process closely enough to be confident that the cellular mechanism is being probed. Probably the experimental factors that are most difficult to control are the uniformity of the vesicles and the constraints that determine their behavior. In most conditions where fusion is triggered, the probability of bilayer mechanical rupture and leakage is increased. Confining that rupture to the contact area remains the most elusive characteristic of cell fusion to mimic. It may depend on fusogenic proteins. Some membrane characteristics, such as lipid asymmetry, may be crucial and may be determined biochemically, but they are difficult to duplicate in model systems. The contact-induced formation of nonbilayer lipid structures triggered by phosphatidylinositol turnover may offer some guidance in how the biochemical and required physical changes may be coupled.

Cations, Divalent↗
PubMed1985

Cryolumpectomy for breast cancer: an experimental study.

The effects of cryosurgical procedures and surgical excision in preventing the local recurrence of mammary adenocarcinoma were studied in BALB/cfC3H mice carrying syngeneic, virus-induced mammary adenocarcinomas transplanted into the fourth mammary fat pad. In this report we present evidence demonstrating that cryosurgical procedures involving multiple freeze-thaw cycles followed by tumor excision markedly reduce the local recurrence rate of mouse mammary cancer. Surgical resection without cryotreatment resulted in an 80% local recurrence rate; in contrast, cryotreatment consisting of three freeze-thaw cycles before excision prevented local tumor recurrence in 70% of the animals. The use of cryotherapy and local excision (cryolumpectomy) in the treatment of human breast cancer is discussed.

Adenocarcinoma↗
PubMed1985

Dynamic morphology of calcium-induced interactions between phosphatidylserine vesicles.

Structural changes in phosphatidylserine vesicles exposed to calcium chloride for various times have been observed by means of video-enhanced light microscopy and freeze-fracture electron microscopy. Large flat double-bilayer diaphragms form at the contacts between aggregated vesicles within milliseconds. Bilayers at and outside of diaphragms rupture and allow vesicles to collapse completely by flattening against each other within seconds. Collapse through intermediate states to a stable multilamellar phase is complete within minutes. The Ca-induced attraction energy and the resultant flattening at contacts between vesicles is far beyond that needed to stress bilayers to the point of rupture. Although the destabilizing response to this stress is preferential to the diaphragm region, 40% of adhering pairs rupture outside of the diaphragm region rather than fuse with each other. In this respect the mechanism of fusion between these vesicles may be fundamentally different from the controlled fusion process in cells.

Calcium Chloride↗
PubMed1984

Diacylglycerol causes major structural transitions in phospholipid bilayer membranes.

We demonstrate for the first time that major structural changes are imposed on various phospholipid bilayers by diacylglycerol, a product of phosphatidylinositol metabolism. By 5 mole percent in phosphatidylethanolamine a lamellar to hexagonal transition starts that is complete at 10 mole percent. At 30 mole percent it causes the same transition in phosphatidylcholine and forms a cubic phase at 80 mole percent. Diacylglycerol disorders the phosphatidylserine lamellar phase. We view the formation of the non-lamellar phases as diagnostic of the destabilizations that diacylglycerol can cause in membranes. We suggest how DAG may act both in its specific activation of membrane enzymes and in inducing membrane fusion.

Animals↗
PubMed1984

Lessons for the study of membrane fusion from membrane interactions in phospholipid systems.

'Fusion' in model systems usually refers to the decay of membrane configurations that are inherently unstable because of the method of preparation. Natural fusion is a controlled event during which the underlying forces and instabilities are subject to the additional effects of biochemical reactions. To understand biological fusion one must be able first to assess the interplay among these physical and chemical factors. This paper reviews traditional measurements of electrostatic double layer and electrodynamic van der Waals forces acting between bilayer membranes. It also describes the much stronger hydration forces that have now been systematically studied. An essential part of any fusion event is the ability of membrane surfaces to overcome or circumvent the hydration barrier in order to make contact. This may be accomplished through applied force, through bridging substances that displace water from the membrane surface, or through biochemical modification of surfaces. In model systems, destruction of the hydration layer can cause violent adhesion, membrane deformation, and rupture. Natural fusion proceeds by more subtle processes whereby interfacial forces are harnessed in ways not yet understood.

Animals↗
PubMed1984

Physical force considerations in model and biological membranes.

We have emphasized the general lessons learned by measuring the forces between and within many kinds of phospholipid bilayers. Interbilayer forces within about 30 A separation (1 A = 0.1 nm) are dominated by a strong hydration repulsion that we believe exists for all interacting hydrophilic surfaces. This hydration can be characterized by the polarization properties of water. Its decay with distance is common to all hydrophilic surfaces, while its strength is characteristic of the specific surface groups. Interactions at distances greater than 30 A between surfaces charged by adsorbed ions or by dissociation of surface groups qualitatively follow expectations for electrostatic double-layer forces, but quantitatively reveal an influence by the long-range hydration on electrostatic double layers. Bilayer lateral pressures and compressibilities, measured at thermodynamic equilibrium, are nonlinear and highly dependent on lipid species. Comparison with monolayers is not possible, since the latter are usually metastable states. In applying these results to contact and fusion of phospholipid vesicles, we define weak and strong regimes of interbilayer force, the former being too weak to overcome the hydration barrier. The special case of divalent cation binding with acidic phospholipids provides sufficient attraction to compete with hydration repulsion. However, such attraction will distort vesicles to rupture. Any observed fusion in such systems may be incidental to this destruction. This suggests that the control of biological membrane fusion, divalent cation antagonism, and postfusion stability is lacking in these systems. Biological fusion more likely involves focal biochemical change simultaneous with reduction of the hydration forces.

Animals↗
PubMed1983

Membrane interaction and deformation.

Membrane interaction and membrane deformation should be considered two aspects of the same phenomenon. Because membrane interaction depends on structural features such as curvature, chemical composition, and surface organization, one must expect that these features will change as membranes are brought together. Our observations on model phospholipid membranes have allowed us to measure and to distinguish electrostatic (coulombic or double-layer) forces, electrodynamic (van der Waals, dispersion) interactions, and hydration forces due to the solvation of polar groups that are stabilizing the membrane surface. As a consequence of these interactions, approaching membranes may flatten against each other, may change the packing density of their constituent molecules, may rearrange the composition of components in regions close to the apposing membrane, or may even show conformational changes in the arrangement of the lipid hydrocarbon chains. Abundant examples of such deformation accompanying membrane interaction are evident from x-ray diffraction and electron microscopic observations.

Cell Communication↗
PubMed1983

Membrane transport and the activity of water near the membrane surface.

In this paper we have mentioned several properties of membrane boundary water in the context of the transport processes discussed at this meeting. Any surface covered with water soluble groups will necessarily lower the free energy density of water solvent in its immediate vicinity. The clearest manifestation of this effect is the work required to push together two such surfaces squeezing out the intervening fluid. This "hydration" repulsion grows exponentially and depends negligibly on surface charge and ionic strength of the medium. Below 20 A separation it dominates all other interactions (unless there be present another material that competes successfully with water for the membrane surface). Boundary water appears to exclude some solutes such as small sugars but is hospitable to ions. Ionic transport is thus surprisingly well-modeled by several conflicting theories all of which treat water as an ideal continuum material. Transport by vesicular contact and fusion is probably arrested by membrane hydration. Factors which weaken or overcome hydration forces are known to facilitate fusion while fusion is suppressed by factors which increase membrane hydration.

Animals↗
PubMed1982

Effects of monovalent ion binding and screening on measured electrostatic forces between charged phospholipid bilayers.

In an effort to determine the role that monovalent ions play in the modification of intermembrane forces, we have measured these forces between charged phospholipid bilayers in monovalent ionic solutions. The osmotic stress technique allowed the net electrostatic pressure between the bilayers to be measured while their separation was concurrently determined by x-ray diffraction. Taken together, these measurements yielded electrostatic pressure as a function of bilayer separation. We have related measured pressures to the bilayer surface charge density and surface potential through an exact solution of the full nonlinear Poisson-Boltzmann equation for this system. Quantitative differences in bilayer separation amongst monovalent alkali metal cations indicated differential binding of these to phosphatidylglycerol (PG), phosphatidylserine (PS), and phosphatidic acid (PA); binding affinity series were determined for Li+, Na+, K+, Cs+, and TMA+ ions to these lipids. The anions Cl-, Br-, I-, and CH3COO- were found to have no differential effect on the repulsive forces between PS bilayers. Debye lengths for the electric double layer estimated from the slopes of the experimental pressure curves were consistently longer than predicted on the basis of classic Gouy-Chapman theory. Estimates of the van der Waals Hamaker coefficient between bilayers of PS and PG in salt solution were found to be weaker than between phosphatidylcholine bilayers in pure water, a difference possibly due to electromagnetic retardation and ionic screening.

Animals↗