Search PubMed⌕ Search

Biomedical subjects

S R Caplan

Publications and source records attributed to S R Caplan.

At least 55 records · Page 3Linked to original sources
PubMed1980

Effect of ouabain on electrical conductance of frog skins. Evidence against recycling of sodium.

Ouabain (10(-4) M) added to the serosal solution of isolated frog skin not only stops the active transport of Na+ but causes a dramatic increase in the electric conductance of the skin. The effect also appears when ouabain is added to amiloride-pretreated skins, ruling out the possibility of a cellular effect. The similarity between the effect of ouabain on normal and amiloride-pretreated skins indicates that no appreciable recycling of Na+ across the basolateral membrane of frog skin takes place. The change of Na+ efflux after ouabain is added to amiloride-pretreated skins parallels the change of electric conductance, indicating that besides blocking the Na+ pump, ouabain affects the paracellular shunt pathway between the cells.

Amiloride↗
PubMed1980

Photoelectric conversion by bacteriorhodopsin in charged synthetic membranes.

Photoelectroactivity of oriented purple membrane layers attached to an ion exchange film has been investigated. The action spectrum of the photocurrent followed the absorption spectrum of bacteriorhodopsin. The intactness of structure and function of bacteriorhodopsin was demonstrated by studies of absorption and photocycle kinetics. The direction of the photocurrent suggests that the extracellular surface of purple membrane is more positive. Photocurrents as high as 20 microA cm-2 were obtained in some preparations. The dependence of steady-state photocurrents on intensity of illumination and temperature was also studied. The initial rate of build-up of photocurrent depends linearly on the intensity of illumination while the off rate does not exhibit any dependence on the intensity of illumination. With rise in temperature an increase in the steady state photocurrent has been observed. This dependence was found to be linear when increase of the photocurrent due to proton translocation alone was considered.

Bacteriorhodopsins↗
PubMed1980

Preparation and characterization of inverted cell envelopes of Halobacterium halobium.

Inside-out cell envelopes from Halobacterium halobium R1M1 have been isolated by sonication and subsequent sucrose-density-gradient fractionation. The inverted cell envelopes transport protons from the exterior of the vesicles by a light-dependent, uncoupler-inhibited process. Enzymes usually facing the inside of the cell are exposed to the external medium in this preparation.

Bacteriorhodopsins↗
PubMed1980

Suppression of gastric acid secretion by furosemide in isolated gastric mucosa of guinea pig.

The effect of furosemide on acid secretion and Cl- transport was studied in isolated fundic mucosa of the guinea pig. Furosemide (10(-3) M), applied to the serosal side produced an immediate effect on the short-circuit current (Isc), lowering it by 47 +/- 2%. Potential difference decreased by 29 +/- 3%, electrical conductance by 18 +/- 4%, acid secretion by 38 +/- 1%, and net flux of Cl- from serosal-to-mucosal side by 37%. Application of the drug to the mucosal side produced similar effects on acid secretion and on the electrical parameters. It is suggested that furosemide blocks the entrance of Cl-, by the Na+--Cl- cotransport mechanism, through the basolateral membrane of the secreting cell. The consequent reduction in electrogenic Cl- transport would cause Isc and acid secretion to decrease. A reduction of Cl- conductance of the apical membrane, upon mucosal application of the drug, would cause similar effects on acid secretion and Cl- transport.

Animals↗
PubMed1979

Interaction of purple membrane with solvents. I. Applicability of solubility parameter mapping.

We carried out spectral studies on the interaction between purple membrane fragments (isolated from Halobacterium halobium) and a series of different solvents, classified quantitatively according to their solubility parameters delta d, delta p, delta h. These represent the contribution of dispersion forces, polar forces, and hydrogen bonding, respectively, to the cohesive energy density of the solvent. Purple membrane fragments, kept in the dark, were suspended in each of the solvents as well as in binary mixtures of solvents, and the spectrum of the resulting suspension was recorded in the wavelength region 250-700 nm. The interaction of each solvent with the membrane fragments can be represented by a point on either a ternary diagram, where each of the three axes represents one of the solubility parameters, or a binary diagram, where one of the two axes is a combination of two of the solubility parameters (delta v = square root of delta d2 + delta p2 or delta a = square root of delta p2 + delta h2). In the former type of solvent map the contribution of each of the parameters is distinct but only their relative contributions are expressed. In the latter the absolute values of delta i are considered. In each of these modes of presentation an inner closed region is observed. The solvents inside its borders interact with bacteriorhodopsin with a resultant spectral change. Mixtures of solvents fit the maps according to their calculated delta values. Thus, a mixture of an apolar solvent with a highly polar solvent interacts with bacteriorhodopsin, even though each of these solvents alone does not.

Bacteriorhodopsins↗
PubMed1979

Interaction of purple membrane with solvents. II. Mode of interaction.

Using the solubility parameter mapping technique (Eisenbach, M., Caplan, S.R. and Tanny, G (1979) Biochim. Biophys. Acta 554, 269-280) we studied spectroscopically the mode of interaction between the purple membrane of Halobacterium halobium and pure organic solvents or solvent mixtures. Although the interacting solvents formed a well-defined closed region in the interaction maps, mapping the modes of interaction did not reveal a closed region for each spectrally classifiable type. A suggested interpretation for this is that interaction with the purple membrane chromophore requires that a solvent (or solvent mixture) possess apolar groups in order to obtain access to the chromophore, together with a polar character and hydrogen-bonding capacity. The mode of interaction, however, is dependent on the specificity of the reactive group of the solvent for retinal, and this has nothing to do with membrane properties. We also examined the influence of the duration of the interaction and of illumination. Some solvents appeared to react more sluggishly than others, but no generalization in terms of the solubility parameter mapping was found, probably because the map describes thermodynamic rather than kinetic phenomena. The only effect of illumination was to enhance the reaction of some of these solvents. It did not change the solubility parameters of purple membrane.

Bacteriorhodopsins↗
PubMed1979

Light-induced pH changes in sub-bacterial particles of Halobacterium halobium. Effects of ionophores.

The kinetics of light-induced acidification and of the subsequent dark-induced alkalization in suspensions of sub-bacterial particles of Halobacterium halobium may be expressed as the sum of two exponentials, indicating two processes (Eisenbach, M., Bakker, E.P., Korenstein, R. and Caplan, S.R. (1976) FEBS Lett. 71, 228--232). We studied the effects of carbonyl cyanide p-trifluoromethyoxy phenyl-hydrazone, nigericin, gramicidin D, valinomycin, and monactin on the extents and the rate constants of the two processes. The various ionophores affected the two processes differently and in general the slower process was more sensitive to their presence. Valinomycin and monactin had relatively minor effects, apparently due to the high ionic strength of the suspension. When an artificial membrane potential was created in the dark, the light-induced acidification was preceded by a transient alkalization as is usually observed in intact cells. These results are discussed in the light of a suggested model accounting for the two processes (Caplan, S.R., Eisenbach, M., Cooper, S., Garty, H., Klemperer, G. and Bakker, E.P. (1977) in Bioenergetics of Membranes (Packer, L., Papageorgiou, G.C. and Trebst, A., eds.), pp. 101--114, Elsevier/North-Holland Biomedical Press, Amsterdam), taking into account the different selectivities of the ionophores applied.

Anti-Bacterial Agents↗
PubMed1979

Light-induced conductivity changes in purple membrane suspensions.

Small light-induced changes in the conductivity of light-adapted purple membrane suspended in strong electrolyte solutions were detected. The method used involved modulated light and a phase sensitive detector and it allowed us to detect accurately changes as small as 0.0001% in the conductivity of the suspension. The light-induced conductivity changes turned out to be composed of at least two different event: a small fast increase in conductivity (tau approximately 2 ms) followed by a slower and larger decrease in this parameter (tau = 70 ms-80 ms). The effects of pH and temperature on these changes were studied. Both events reached maximal values around neutral pH and approached zero at both high and low pH's. Heating the suspension decreased the photoconductivity change and Arrhenius plots of the data showed breaks around 31 degrees C. It is suggested that the conductivity changes reflect changes in the surface charge of the membrane and can be used to follow the kinetics of the conformational changes occurring in the system.

Bacteriorhodopsins↗
PubMed1979

Measurement of oxygen consumption in voltage-clamped epithelia.

Standard apparatus for in vitro study of anuran epithelia was adapted for the incorporation of Clark oxygen electrodes, permitting the concurrent measurement of electrical current (active sodium transport) and oxygen consumption under voltage-clamp conditions, with independent manipulation of the two bathing solutions. Stability was enhanced by electrical isolation of the O2 electrodes, sensitive temperature control (+/- 0.03 degrees C), and constancy of stirring rate. Mean rate of drift was less than 3.7% of the average rate of basal (i.e., nontransport related) O2 consumption. In the present configuration the response time was less than 15 s. Visual fitting of slopes of O2 tension evaluated rates of O2 consumption with adequate accuracy in the physiological range (basal rates averaged about 20 pmol-s-1-cm-2 toad bladder, corresponding to about 10 pmol-s-1-mg-1 dry wt, or about 5 pmol-s-1-ml-1 chamber volume). Rpresentative slopes were read with a standard deviation of 3.5%.

Animals↗
PubMed1979

The use of linear nonequilibrium thermodynamics in the study of renal physiology.

Classical formulations for the analysis of membrane transport processes, which ignored possible interactions between flows of diverse permeant species, often led to inconsistencies in the evaluation of permeability coefficients. For water flow induced by an osmotic pressure difference this difficulty was resolved by Staverman's introduction of the reflection coefficient sigma, a parameter which incorporates the interaction between solute and solvent in the course of their passage through a membrane. A comprehensive nonequilibrium thermodynamic (NET) formalism suitable for many biological systems was provided by Kedem and Katchalsky. For an n-flow system each flow is in general dependent on n forces; the assumption of Onsager reciprocity, however, reduces the number of independent phenomenological coefficients. Although NET is widely applied in the study of renal physiology, fundamental theoretical and practical problems remain. Basic considerations are the need to control or evaluate the influence of all coupled flows and to establish conditions fostering linear dependencies of flows on forces. When this is done a transport system may be characterized in terms of intrinsic membrane parameters, facilitating the systematic study of the effects of drugs, hormones, and various experimental perturbations.

Biological Transport, Active↗
PubMed1978

Proteolysis and flash photolysis of bacteriorhodopsin in purple membrane fragments.

Pronase treatment of aqueous suspensions of purple membrane fragments from H.halobium leads to the cleavage of bacteriorhodopsin. The protein fragments remaining in the membrane after treatment with relatively small concentrations of enzyme (2% w/w) in normal daylight range in molecular weight from 20,000--21,000 daltons, indicating that cleavage occurs mainly near the extremities of the protein chain. At higher enzyme concentrations the relative amounts of protein fragments having smaller molecular weight increase. Generally, the relative loss of retinal chromophore is larger than that of protein and thus the retinal binding site seems to be located near one of the chain ends that is cleaved off by enzyme. Irradiation with white light during the time of proteolysis (at both low and high enzyme concentrations) results in extensive cleavage, so that under certain conditions no high molecular weight components can be detected in SDS-polyacrylamide gels. It, therefore, appears that parts of the bacteriorhodopsin chain become more exposed to enzyme digestion when the purple membrane is illuminated. Enzyme treated aqueous purple membrane fragment suspensions still show photocycle activity. The main consequence of proteolysis is a pronounced appearance of biphasicity in the decay of M412 and the regeneration of bR570. Simultaneously the yield of O660 is reduced. As with untreated purple membrane, the correlation between the rates of decay of M412 and regeneration of bR570 is greatest when the yield of O660 is lowest.

Bacterial Proteins↗
PubMed1978

Phospholipid substitution of the purple membrane. The stoichiometry of light-induced proton release by phospholipid-substituted purple membranes.

The method of Warren et al. (1974, Proc. Natl. Acad. Sci. U.S. 71, 622--626) was employed to substitute the polar lipids of the purple membrane of Halobacterium halobium by different phosphatidylcholine species. Substitution at pH 6.5 yields proteolipid complexes in the form of bent open sheets which have a protein to lipid phosphorus ratio similar to the natural membrane, i.e. about 1 : 10 (mol/mol). The extent of substitution increases with the length of the fatty acid chain of the phosphatidylcholine used. The spectral properties of bacteriorhodopsin are only slightly affected by substitution of 95% of the lipid, except that the photocycle is slowed down appreciably. Due to this slow rate the M412 intermediate of the cycle accumulates in the light. Associated with this accumulation is a net light-induced proton release, which proved insensitive to uncoupler. A comparison between the net proton release and the amount of M412 accumulated, studied as a function of pH, shows that no fixed stoichiometry exists between the two processes. Phospholipid substitution by egg phosphatidylcholine at pH 7.5 or by egg phosphatidylethanolamine leads to preparations of purple membrane with 15 or 25 mol of phospholipid per mol of bacteriorhodopsin, respectively. These preparations seem to consist of closed membrane structures. They take up protons in the light in an uncoupler-sensitive way.

Bacteriorhodopsins↗
PubMed1978

Influence of membrane lipids on the photochemistry of bacteriorhodopsin in the purple membrane of Halobacterium halobium.

Purple membrane fragments from Halobacterium halobium were reconstituted with the native lipids replaced by dipalmitoyl phosphatidylcholine and by egg lecithin. In parallel studies the temperature dependence of bacteriorhodopsin phototransient lifetime and absorption dichroism and of in situ lipid microviscosity were determined; the former two by, respectively, conventional and polarization flash photometry, and the latter by observation of emission depolarization of an embedded fluorescent dye, 1,6-diphenyl-1,3,5-hexatriene. Discontinuities in lipid microviscosity profiles in native and egg lecithin purple membrane were reflected in both the photochemical cycle frequency and bacteriorhodopsin chromophore rotational mobility. The influence exerted by membrane-lipid viscosity appears to be a secondary effect, and points to the bacteriorhodopsin chromophoric group being situated in the protein interior.

Bacteriorhodopsins↗
PubMed1978

Bacteriorhodopsin: lipid environment and conformational changes.

The polar lipids of the purple membrane were exchanged for different phosphatidylcholine species. The resulting complexes had the same protein to lipid-phosphorus ratio as the natural membrane, but only about 0.5-1.0 mole of original lipid was still present per mole of bacteriorhodopsin. In such complexes the bacteriorhodopsin photocycle is slowed down 10-20 times, but the strong protein-protein interaction is not abolished. Due to the slow rate of the photocycle we were able to measure in the light the ratio between net proton release and net accumulation of the last intermediate of the photocycle, the unprotonated M412. This ratio was not constant and equal to 1.0, as expected for a single deprotonation reaction, but varied with pH from 1.5 to 0.4. The variable ratio suggests that light-induced conformational changes occur in the nonchromophore part of the protein, which shift the pKa values of unidentified groups so as to cause binding or release of additional protons. A similar conclusion was drawn from experiments on the kinetics of proton transfer by bacteriorhodopsin in subbacterial particles of Halobacterium halobium and in reconstituted bacteriorhodopsin proteoliposomes. However, in this case light-induced association and dissociation of additional protons occurs simultaneously on different sides of the membrane.

Bacteriorhodopsins↗