Description by quasi elastic laser light scattering of a biological preparation: sarcoplasmic reticulum vesicles

Halothane-induced functional and structural modifications in sarcoplasmic reticulum membranes from pig skeletal muscle

We investigated the effect of halothane on lipid and protein components of sarcoplasmic reticulum membranes isolated from pig trapezius muscle. We studied the relationships between the (Ca2(+)-Mg2+)-ATPase activity and the interaction of the anesthetic with lipid and protein moieties by means of EPR and fluorescence spectroscopic techniques. Our results clearly show that below 5 mumol per mg protein, halothane interacts mainly with the lipid components of the membrane. This interaction is shown to be localized in the central core of the phospholipid bilayer and to induce an increase of the membrane calcium permeability. The interaction with protein components only occurs at higher halothane concentrations and affects its conformational and functional states. These results are discussed with respect to new insights into diethylether-SR membrane interaction and to malignant hyperthermia syndrome in the pig.

Interaction of the local anesthetics dibucaine and tetracaine with sarcoplasmic reticulum membranes. Differential scanning calorimetry and fluorescence studies

The local anesthetics dibucaine and tetracaine inhibit the (Ca2+ + Mg2+)-ATPase from skeletal muscle sarcoplasmic reticulum [DeBoland, A. R., Jilka, R. L., & Martonosi, A. N. (1975) J. Biol. Chem. 250, 7501-7510; Suko, J., Winkler, F., Scharinger, B., & Hellmann, G. (1976) Biochim. Biophys. Acta 443, 571-586]. We have carried out differential scanning calorimetry and fluorescence measurements to study the interaction of these drugs with sarcoplasmic reticulum membranes and with purified (Ca2+ + Mg2+)-ATPase. The temperature range of denaturation of the (Ca2+ + Mg2+)-ATPase in the sarcoplasmic reticulum membrane, determined from our scanning calorimetry experiments, is ca. 45-55 degrees C and for the purified enzyme ca. 40-50 degrees C. Millimolar concentrations of dibucaine and tetracaine, and ethanol at concentrations higher than 1% v/v, lower a few degrees (degrees C) the denaturation temperature of the (Ca2+ + Mg2+)-ATPase. Other local anesthetics reported to have no effect on the ATPase activity, such as lidocaine and procaine, did not significantly alter the differential scanning calorimetry pattern of these membranes up to a concentration of 10 mM. The order parameter of the sarcoplasmic reticulum membranes, calculated from measurements of the polarization of the fluorescence of diphenylhexatriene, is not significantly altered at the local anesthetic concentrations that shift the denaturation temperature of the (Ca2+ + Mg2+)-ATPase.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser light scattering determination of size and dispersity of synaptosomes and synaptic vesicles isolated from squid (Loligo pealei) optic lobes

Quasi-elastic laser light scattering has been used to investigate the size and dispersity of synaptosomes and synaptic vesicles isolated from optic lobes of the squid Loligo pealei. Synaptosomal fractions were highly polydisperse (mu2/gamma -2 = 0.5) and the mean diameter (-d) ranged from 0.5-2.0 microns. Size distribution histograms yielded two major components - smaller particles (-d approximately 300-700 nm) and a larger group of particles (-d approximately 1,500-5,000 nm). The heterogeneity of the synaptosomal particles detected in solution is in agreement with published data obtained using electron microscopy. Purified synaptic vesicle fractions also yielded complex particle size distribution data. A component with a mean diameter in the range 150-250 nm was detected, though a smaller particle (-d approximately 40-110 nm) dominated the scattering signal. This smaller particle closely resembles in size the electron lucent vesicles seen in the majority of squid optic lobe nerve terminals when examined by electron microscopy. Osmotically-induced shrinkage and swelling of the synaptosomes was detected. Depolarization by veratridine (1.0 x 10(-4) M) did not result in a detectable change in the size of synaptosomal particles.

Quantitative determination of the calcium involved in the regulation of the Ca2+-ATPase activity in sarcoplasmic reticulum vesicles

The dependence of the Ca2+-ATPase activity of sarcoplasmic reticulum vesicles upon the intravesicular concentration of calcium accumulated after active uptake was studied. The internal calcium concentration was modified by addition of the ionophore A23187 at the steady state of accumulation. About half of the calcium accumulated could be released at low ionophore concentration without any concomitant activation of the Ca2+-ATPase. This population of calcium might consist of calcium free in the lumen of the vesicles or bound to the bilayer at sites which do not interact with the ATPase activity. At higher concentrations of ionophore (above 1.75 nmol A23187/mg protein) the release of calcium activated this enzyme. This phenomenon was independent of the extravesicular calcium concentration and might be explained by assuming second species of calcium ions bound to the inner side of the membrane and in close functional interaction with the Ca2+-ATPase.

Effects of local anesthetics on the passive permeability of sarcoplasmic reticulum vesicles to Ca2+ and Mg2+

Sarcoplasmic reticulum vesicles are used here as model membrane system to question the hypothesis of enhancement of permeability of cations by anesthetics, particularly that of Ca2+ and of Mg2+. The effects of dibucaine (up to 800 microM), tetracaine (up to 2 mM), lidocaine (up to 10 mM) and procaine (up to 10 mM) on the permeability of these membranes to Ca2+ and Mg2+ have been measured. We have used an experimental approach based on the light scattering method (Kometani, T. and Kasai, M. (1978) J. Membrane Biol. 41, 295-308). It has been found that all the local anesthetics cited above markedly increase the permeability of sarcoplasmic reticulum vesicles to Mg2+ and, in the concentration range tested herein, only dibucaine and tetracaine increase the permeability to Ca2+. The kinetic analysis of the time dependence of the light-scattering data after the osmotic shock shows that, in the absence of local anesthetics, the Mg2+ influx can be described as proceeding through a unique type of channel. However, Ca2+ influx appears to involve two channel of different kinetic properties. Because the relative fraction of both types of Ca2+ channel is similar to the average ratio between light and heavy vesicles in unfractionated sarcoplasmic reticulum, we suggest that each type of channel can be preferentially located in one of these fractions. The determined rate constants for Ca2+ permeability through both types of channel are 0.77 +/- 0.08 min-1 (fast channels) and 0.025 +/- 0.005 min-1 (slow channels) and that for Mg2+ is 0.08 +/- 0.02 min-1. These results agree with data obtained by other groups using different experimental approaches. Dibucaine and tetracaine significantly alter the rate of Mg2+ and Ca2+ influx through the slow channels. In addition, these two local anesthetics also produce the effect that the Mg2+ influx cannot be described with only one exponential process, thus suggesting a differential effect on vesicles of different density. The increase of Ca2+ and Mg2+ permeability by dibucaine and by tetracaine is found at concentrations of these drugs that do not produce a noticeable inhibition of the (Ca2+ + Mg2+)-ATPase activity of sarcoplasmic reticulum vesicles.

Gel to liquid crystalline phase transition promotes a conformational reorganization of Ca2+, Mg2+-ATPase from sarcoplasmic reticulum in dimyristoylphosphatidylcholine reconstituted systems

Sarcoplasmic reticulum Ca2+, Mg2+-ATPase has been reconstituted in membranes highly enriched in dimyristoylphosphatidylcholine. According to electron microscopy data these membranes form vesicles of an average diameter of 1000 +/- 200 A. These reconstituted membranes show hysteretic behavior in some physical-chemical properties, such as light scattering and fluorescence when labeled with iodoacetamidofluorescein and with N-iodoacetyl-N'-(5-sulfo-1-naphthyl) ethylenediamine. Hysteretic behavior in catalytic activity can also be inferred from the kinetic data presented in this paper, because the temperature dependence of the Ca2+, Mg2+-ATPase activity is altered by a mild thermal pretreatment of the samples. Furthermore, it was noticed that the Ca2+-dependent ATPase activity of these complexes, when assayed above the phase transition temperature (Tc) of the lipid matrix, showed a lag phase in the minute time scale range. On the basis of these findings, it is suggested that the gel-to-liquid crystalline phase transition of the lipid is able to shift the conformational equilibrium E----E* of Ca2+, Mg2+-ATPase. The fact that the -SH reactivity against 5,5'-dithio-bis-nitrobenzoic acid of these complexes is also altered by preincubation above Tc for several minutes also supports that lipid melting induces a conformational change in Ca2+, Mg2+-ATPase.

Study of the electrokinetic properties of reconstituted sarcoplasmic reticulum vesicles

A study of electrokinetic properties of reconstituted sarcoplasmic reticulum was undertaken to determine the nature of the groups bearing the negative charge of the membrane. After incorporation of phosphatidylcholine into the bilayer, it was found that the Ca2+-ATPase embedded in functional vesicles bore 3e- per mole. When the surface charge density of the hydrodynamic particles became more negatively charged by incorporation of phosphatidylserine molecules, the reconstituted vesicles had a tendency to build large structures resulting from vesicle-vesicle interaction and containing large amounts of divalent cations. These aggregated structures may partially explain the discrepancy observed between the expected value of the surface charge density and the data obtained by electrophoretic mobility measurements. This work emphasizes the importance of a renewal of the classical interpretation of electrophoretic mobility data in order to analyze the results obtained with biological material. To explain the energy transduction process which takes place in the sarcoplasmic reticulum membrane, it was of interest to determine whether or not variations of the surface electrical properties affect the calcium ion translocation upon ATP hydrolysis. Relatively significant modifications of the bilayer composition and surface charge density did not appreciably affect the calcium transport activity.

Electrokinetic and hydrodynamic properties of sarcoplasmic reticulum vesicles: a study by laser Doppler electrophoresis and quasi-elastic light scattering

The electrical properties of sarcoplasmic reticulum vesicles were studied using electrophoretic mobility measurements by laser Doppler velocimetry. Combined with quasi-elastic light scattering analysis, this method enabled us to monitor changes in membrane surface charge density upon addition of NaCl, CaCl2, and MgCl2 solutions. At low ionic strength (4.7 mM), and in the absence of divalent salts, sarcoplasmic reticulum vesicles displayed a zeta potential value of -32.6 mV and a surface charge density of 5.4 10(-3) C/m2, corresponding to one elementary negative charge per 30 nm2 or about 2900 negative charges per vesicle. Upon addition of NaCl (up to 100 mM) vesicles became more negative (from 2900 to 6200 negative charges per vesicle), suggesting chloride binding or adsorption on the membrane. A noticeable increase of the vesicular size was observed upon addition of calcium or magnesium (25 to 30% increase of the hydrodynamic radius for 2.5 mM CaCl2 or MgCl2). This effect was prevented or suppressed by addition of relatively low concentrations of NaCl (50 mM). At low divalent cation concentrations one-third of the total net charge of the vesicles was neutralized suggesting a specific binding of cation on the membrane. At higher salt concentrations no modification of this parameter was observed. These results support the Gouy and Chapman theory about the electrical properties of sarcoplasmic reticulum vesicles.

Inactivation of sarcoplasmic reticulum (Ca2+ + Mg2+)-ATPase by N-cyclohexyl-N'-(4-dimethylamino-alpha-naphthyl)carbodiimide

The synthesis and characterisation of N-cyclohexyl-N'-(4-dimethylamino-alpha-naphthyl)carbodiimide (NCD-4) is described. Only the N-acetylurea and urea corresponding to NCD-4 are appreciably fluorescent: the O-phenylisourea and S-ethylisothiourea derivatives have negligible fluorescence. NCD-4 inhibits the (Ca2+ + Mg2+)-ATPase of sarcoplasmic reticulum irreversibly: Ca2+ protects against inhibition. Covalent incorporation of NCD-4 occurs into the Ca2+-protected sites, with a stoichiometry of approximately 1 mole/mole of ATPase. The modified enzyme has fluorescence emission properties similar to those of NCD-4 N-acetylurea in a relatively hydrophobic environment: it is concluded that NCD-4 has modified a carboxylate group (s) located in or near the Ca2+-binding sites of the ATPase.

Inhibition of a voltage-dependent cation channel in sarcoplasmic reticulum vesicles by caesium studied by using a potential-sensitive cyanine dye

The effect of caesium on the cation transport system in sarcoplasmic reticulum vesicles has been analysed kinetically through Tris+ influx. The Tris+ influx was measured by following the change in K+ diffusion potential due to the mutual diffusion between K+ and Tris+ in the presence of valiomycin using a potential probe; 3,3'-dipropylthiadicarbocyanine iodide. The main results were as follows. (1) Tris+ influx increased when membrane potential became inside-negative. This suggests that Tris+ permeates through the channel which has a voltage-dependent gate. (2) Cs+ reacted with the cation transport system only from the outside of the vesicle and inhibited Tris+ influx. The inhibition follows a single-site titration curve with a voltage-dependent dissociation constant of 18 mM at -60 mV. The inhibition can be explained by assuming that Cs+ binds to a site located about 45% of the way through the membrane from the outside of the vesicle in the open state of the channel. These results are in good agreement with those reported by Coronado and Miller (Coronado, R. and Miller, C. (1979) Nature 288, 495-497), which were gained electrically by using sarcoplasmic reticulum vesicles incorporated into an artificial planar phospholipid bilayer.

Sarcoplasmic reticulum vesicles from trembler mice: a comparison with material obtained from normal animals

Sarcoplasmic reticulum (SR) vesicles were purified from trembler and normal mice. Comparison of their chemical composition showed that the only differences lay in their phospholipid content, the most obvious modification being the presence of lysophosphatidylcholine in preparations obtained from trembler animals. A significant increase of the Ca2+-stimulated ATPase activity promoted a drastic loss in the efficiency of the calcium pumping system of the membrane purified from trembler mice. It is suggested that the modification of the phospholipid content might explain this effect.

Determination of reflection coefficients for various ions and neutral molecules in sarcoplasmic reticulum vesicles through osmotic volume change studied by stopped flow technique

Osmotic volume change of sarcoplasmic reticulum vesicles was studied by following the change in light-scattering intensity using a stopped flow apparatus. From the analysis of the initial rate of scattering change, reflection coefficients for various ions and neutral molecules were determined. The following are typical results: K+, 0.72; Tris+, 0.98; choline 1; NO3-, 0.32; Cl-, 0.46; methanesulfonate, 0.62; gluconate, 0.96; glycerol, 0.86; and glucose, 1. When the K+ permeability was increased in the presence of 10(-6) g valinomycin/ml, the reflection coefficient for K+ changed from 0.72 to 0.31. It was found that there was a close relationship between the reflection coefficients and the permeabilities of the solutes. Hydraulic conductivity was also determined from the initial rate of light scattering change and was not different for the different solutes. The water permeability was estimated to be 2.1 x 10(-3) cm/sec at 23 degrees C.

[Stoichiometry of calcium transport by sarcoplasmic reticulum: utilization of p-nitrophenylphosphate as an energy donor]

We have studied, under different conditions and through the hydrolysis of p-nitrophenylphosphate, the stoechiometry of the active transport of calcium by sarcoplasmic reticulum. According to a minimal kinetic model, it is possible to explain the variation of the coupling factor n(t) during the calcium accumulation in absence of precipitating agent. Under the described experimental conditions, at the beginning of the experiment, the coupling factor's value is slightly above 2.

Ionic permeability of sarcoplasmic reticulum vesicles measured by light scattering method

The volume change of sarcoplasmic retriculum vesicles was followed by measuring the light scattering intensity. When the salt concentration of the suspension of sarcoplasmic reticulum vesicles was increased by using a stopped flow apparatus, the light scattering intensity rapidly increased at the beginning and then decreased. The fast increase in the light scattering intensity is caused by the decrease of the volume of sarcoplasmic reticulum vesicles due to the outflow of water. The following decrease in the light scattering intensity is caused by the increase of the volume due to the inflow of the solutes and water. From the former and the latter rates, the permeation times of water and the solutes could be calculated, respectively. According to the same method, permeation times of various salts were determined. The rate of the inflow of the salts was dependent on the movement of the slower ions, that is, ions move as a pair. In the case of potassium salts, an increase in the permeation rate of the salts was observed when valinomycin was added to the membrane suspensions. From these experiments, as a measure of permeability, half permeation times of various ions and molecules were determined. The following are typical results: water 0.1, Li+ 36, Na+ 26, K+20, Rb+ 16, Cl- 0.4, methanesulfonate 20, phosphate 10.5, oxalate 40 in seconds at room temperature. As a whole, sarcoplasmic reticulum was found to be an anion permeable membrane.

Dynamic light scattering study of calcium-induced fusion in phospholipid vesicles

Acidic sonicated phospholipid vesicles can undergo dramatic morphological changes due to fusion in the presence of divalent metal ions. For example, small spherical phosphatidylserine vesicles can form scroll-like cylinders which precipitate in the presence of Ca2+ above a threshold concentration. Subsequent addition of EDTA will yield large, unilamellar vesicles. These events have previously been established through the combined use of differential scanning calorimetry and freeze-fracture electron microscopy. We have applied the technique of dynamic light scattering to follow these fusion events rapidly, accurately, and non-perturbatively as they occur in solution at calcium concentrations slightly below threshold for precipitation.

Inactivation of proteases and esterases by halomethylated derivatives of dihydrocoumarins

A series of halomethylated derivatives of dihydrocoumarins has been found to inhibit irreversibly proteases and esterases. alpha-Chymotrypsin, subtilish, elastase are rapidly inactivated in the presence of these compounds, while trypsin, kallicrein, papain are inhibited more slowly. Esterases like acetylcholinesterase and butyrylcholinesterase also lose activity in their presence. Two structural features of these inactivators are essential for inhibition: a reactive cis-ester function and an alkylating function. Analogues of these derivatives having only one of these characteristics are inefficient. Therefore it is suggested that the efficiency of these bifunctional reagents is due to their character of potential "suicide substrates".

Binding of nucleotides ATP and ADP to sarcoplasmic reticulm: study by rate of dialysis

Binding of the nucleotides ATP and ADP by preparations of sarcoplasmic reticulum was investigated by the method of flow dialysis. For ATP, experimental data could not be analyzed directly in terms of binding since a significant though small amount of hydrolysis could be observed even in presence of EDTA. ADP binding could be analyzed and gave a dissociation constant of 10-20 muM at neutral pH, and a stoichiometry of 0.35 - 0.45 per mole ATPase. The possible significance of this stoichiometry is discussed. Similar experiments were performed after ethoxyformylation of sarcoplasmic reticulum which inhibits the Ca2+ dependnet ATPase activity. The results confirmed the inhibition of ATP hydrolysis and pointed to a considerably reduced affinity for nucleotides. The method based on the measurement of dialysis rates is convenient, and accurate enough to detect the effects of chemical modification on sarcoplasmic reticulum membranes.

A light-scattering characterization of membrane vesicles

A technique has been developed in this paper which enables quasi-elastic laser light scattering to be used to accurately and quantitatively measure the average vesicle diffusion coefficient and the relative dispersion in the diffusion coefficient about this average for dilute polydisperse vesicle suspensions. This technique relies on a theoretical analysis of a modified form of the Z-averaged diffusion coefficient. This modified Z-averaged diffusion coefficient explicitly incorporates vesicle size, structure, and polydispersity in a description of the scattered light autocorrelation spectrum. Light-scattering experiments were performed on a dilute, lobster sarcoplasmic reticulum vesicle suspension and the measured average diffusion coefficient and the diffusion coefficient relative dispersion about this average were determined with accuracies of 2 and 10%, respectively. A comparison of vesicle size inferred from light-scattering results was made with size results from electron microscopic analysis of the same sample.