Search PubMed⌕ Search

Biomedical subjects

A Scarpa

Publications and source records attributed to A Scarpa.

At least 271 records · Page 15Linked to original sources
PubMed1977

A direct analysis of lamellar x-ray diffraction from hydrated oriented multilayers of fully functional sarcoplasmic reticulum.

The profile structure of functional sarcoplasmic reticulum (SR) membranes was investigated by X-ray diffraction methods to a resolution of 10 A. The lamellar diffraction data from hydrated oriented multilayers of SR vesicles showed monotonically increasing widths for higher order lamellar reflections, indicative of simple lattice disorder within the multilayer. A generalized Patterson function analysis, previously developed for treating lamellar diffraction from lattice-disordered multilayers, was used to identify the autocorrelation function of the unit cell electron density profile. Subsequent deconvolution of this autocorrelation function provided the most probable unit cell electron density profile of the SR vesicle membrane pair. The resulting single membrane profile possesses marked asymmetry, suggesting that a major portion of the Ca++ -ATPase resides on the exterior of the vesicle. The electron density profile also suggests that the Ca++-dependent ATPase penetrates into the lipid hydrocarbon core of the SR membrane. Under conditions suitable for X-ray analysis, SR vesicles prepared as partially dehydrated oriented multilayers are shown to conserve most of their ATP-induced Ca++ uptake functionality, as monitored spectrophotometrically with the Ca++ indicator arsenazo III. This has been verified both in resuspensions of SR after centrifugation and slow partial dehydration, and directly in SR multilayers in a partially dehydrated state (20-30 percent water). Therefore, the profile structure of the SR membrane that we have determined may closely resemble that found in vivo.

Adenosine Triphosphatases↗
PubMed1977

Intracellular calcium buffering capacity in isolated squid axons.

Changes in ionized calcium were studied in axons isolated from living squid by measuring absorbance of the Ca binding dye Arsenazo III using multiwavelength differential absorption spectroscopy. Absorption changes measured in situ were calibrated in vitro with media of ionic composition similar to axoplasm containing CaEGTA buffers. Calcium loads of 50-2,500 mumol/kg axoplasm were induced by microinjection, by stimulation in 112 mM Ca seawater, or by soaking in choline saline with 1-10 mM Ca. Over this range of calcium loading of intact axoplasm, the ionized calcium in the axoplasm rose about 0.6 nM/muM load. Similar loading in axons preteated with carbonyl cyanide 4- trifluoromethoxyphenylhydrazone (FCCP) to inhibit the mitochondrial proton gradient increased ionized calcium by 5-7 percent of the imposed load, i.e. 93-95 percent of the calcium load was buffered by a process insensitive to FCCP. This FCCP- insensitive buffer system was not saturated by the largest calcium loads imposed, indicating a capacity of at least several millimolar. Treatment of previously loaded axons with FCCP or apyrase plus cyanide produced rises in ionized calcium which could be correlated with the extent of the load. Analysis of results indicated that, whereas only 6 percent of the endogenous calcium in fresh axons is stored in the FCCP-sensitive (presumably mitochondrial) buffer system, about 30 percent of an imposed exogenous load in the range of 50-2,500 muM is taken up by this system.

Adenosine Triphosphate↗
PubMed1977

The concentration of ionized magnesium in barnacle muscle fibres.

1. The total Mg in isolated fibres of Balanus aquila was 10-5 m-mole/kg wet wt. 2. The intracellular free Mg was measured by a null point method using Eriochrome Blue as an indicator of free Mg, and internal dialysis with solutions of varying ionized Mg concentrations. The results indicated a free Mg of 6 mM or 4-2 m-mole/kg wet wt. in the intracellular water immediately surrounding the dialysis capillary. 3. The ATP concentration was estimated to be 4-9 m-mole/kg wet wt. 4. A tentative partitioning of Mg among various intracellular constitutents based on present data combined with published work by others is (m-mole/kg wet wt): free, 4-2; MgATP, 4-2; myofibrillar bound, 1; residual (presumably bound to arginine phosphate and phosphate) ca. 1.

Adenosine Triphosphate↗
PubMed1976

Internal pH of isolated chromaffin vesicles.

The passive permeability of isolated chromaffin vesicles to H+ and the internal pH of the vesicles under various conditions were measured. Potentiometric measurements of K+ and H+ fluxes in the presence of selected ionophores and uncouplers indicated that the membrane is highly impermeable to both protons and potassium. deltapH across the chromaffin granule membrane was measured by [14C]methylamine distribution. At pH 6.85, The deltapH WAS 1.16 WITH THE INTRAVESICULAR SPACE BEING FOUND ACIDIC. Varying the external pH produced an equivalent change in the deltapH, WITH EXTRAPOLATION TO ZERO DEltapH yielding a value of pH 5.5, WHICH IS TAKEN AS AN INDICATION OF THE PH of the intravesicular space. The pH gradient could be enhanced or collapsed by the addition of ionophores and uncouplers under varying ionic conditions. deltapH was constant for granules suspended in various ionic media, suggesting that the deltapH did not arise secondarily due to the establishment of a Donnan equilibrium. The significance of the proton impermeability and deltapH is discussed in terms of regulation of the uptake and storage of catecholamines in bovine chromaffin granules.

Adrenal Medulla↗
PubMed1976

Neuromuscular disorder associated with a defect in mitochondrial energy supply.

A limb muscle biopsy specimen from a patient with a slowly progressive congenital neuromuscular disorder disclosed, by electron microscopy, widespread mitochondrial crystalline inclusions. Biochemical studies of isolated mitochondria showed decreased respiratory rate and respiratory control with both nicotine adenine dinucleotide and flavor-protein-linked substrates. Mitochondrial adenosine triphosphatase (ATPase) activity, both basal and magnesium (Mg++) or 2,4-dinitrophenol- (DNP) stimulated, was greatly reduced in contrast to normal. The rate and extent of mitochondrial calcium accumulation was normal. These findings are consistent with a defect of the respiratory chain-linked energy transfer at a level common to all three energy coupling sites of the respiratory chain. The defect in ATPase activity may be secondary to replacement of functional mitochondrial inner membrane by crystalline inclusions.

Adenosine Triphosphatases↗
PubMed1976

Luft's disease. Further biochemical and ultrastructural studies of skeletal muscle in the second case.

In the second known case of non-thyroidal hypermetabolism (Luft's disease), there were large areas of mitochondrial aggregates in all fibers. Many mitochondria were abnormally large and contained packed cristae. In isolated mitochondrial fractions, studies of oxidative phosphorylation showed defective respiratory control and normal phosphorylation capacity ("loose coupling"). Spectra and content of cytochromes were normal. Basal ATPase activity was seven times greater than normal and poorly stimulated by 2,4-dinitrophenol. The rate of energy-dependent calcium uptake by isolated mitochondria was normal, but the amount of calcium accumulated was much decreased. Calcium could not be retained and was spontaneously released into the medium within 30 seconds. "Recycling" of calcium between mitochondria and cytosol may take place in vivo and result in sustained stimulation of respiration and loose coupling.

Adult↗
PubMed1976

Ionized calcium concentrations in squid axons.

Values for ionized [Ca] in squid axons were obtained by measuring the light emission from a 0.1-mul drop of aequorin confined to a plastic dialysis tube of 140-mum diameter located axially. Ionized Ca had a mean value of 20 x 10(-9) M as judged by the subsequent introduction of CaEGTA/EGTA buffer (ratio ca. 0.1) into the axoplasm, and light measurement on a second aequorin drop. Ionized Ca in axoplasma was also measured by introducing arsenazo dye into an axon by injection and measuring the Ca complex of such a dye by multichannel spectrophotometry. Values so obtained were ca. 50 x 10(-9) M as calibrated against CaEGTA/EGTA buffer mixtures. Wth a freshly isolated axon in 10 mM Ca seawater, the aequorin glow invariably increased with time; a seawater [Ca] of 2-3 mM allowed a steady state with respect to [Ca]. Replacement of Na+ in seawater with choline led to a large increase in light emission from aequorin. Li seawater partially reversed this change and the reintroduction of Na+ brought light levels back to their initial value. Stimulation at 60/s for 2-5 min produced an increase in aequorin glow about 0.1% of that represented by the known Ca influx, suggesting operationally the presence of substantial Ca buffering. Treatment of an axon with CN produced a very large increase in aequorin glow and in Ca arsenazo formation only if the external seawater contained Ca.

Aequorin↗
PubMed1976

Ion permeability of isolated chromaffin granules.

The passive ion permeability, regulation of volume, and internal pH of isolated bovine chromaffin granules were studied by radiochemical, potentiometric, gravimetric, and spectrophotometric techniques. Chromaffin granules behave as perfect osmometers between 340 and 1,000 mosM in choline chloride, NaCl, and KCl as measured by changes in absorbance at 430 nm or from intragranular water measurements using 3H2O and [14C]polydextran. By suspending chromaffin granules in iso-osmotic media of various metal ions and selectively increasing the permeability to either the cation or the anion by intrinsically permeable ions or specific ionophores, it was possible to determine by turbidity and potentiometric measurements the permeability to the counterion. These measurements indicate that the chromaffin granule is impermeable to the cations tested (Na+, K+, and H+). Limited H+ permeability across the chromaffin granule membrane was also shown by means of the time course of pH re-equilibration after pulsed pH changes in the surrounding media. The measurement of [14C]methylamine distribution indicates that a significant deltapH exists across the membrane, inside acidic, which at an external value of 6.85 has a value of 1.16. The deltapH is relatively insensitive to changes in the composition of the external media and can be enhanced or collapsed by the addition of ionophores and uncouplers. Measurement at various values of external pH indicates an internal pH of 5.5. Use of the ionophore A23187 indicates that Ca++ and Mg++ can be accumulated against an apparent concentration gradient with calcium uptake exceeding 50 nmol/mg of protein at saturation. These measurements also show that Ca++ and Mg++ are impermeable. Measurement of catecholamine release under conditions where intravesicular calcium accumulation is maximal indicates that catecholamine release does not occur. The physiological significance of the high impermeability to ions and the existence of a large deltapH are discussed in terms of regulation of uptake, storage, and release of catecholamines in chromaffin granules.

Adrenal Medulla↗
PubMed1975

Calcium binding to cardiac sarcolemma.

Studies with a sarcolemma preparation from guinea pig hearts revealed two classes of Ca2+ binding sites: high affinity sites (Km' of 16 muM) and a 10-fold greater number of low affinity sites (Km' of 800 muM). Low affinity Ca2+ binding was inhibited by ruthenium red and verapamil, suggesting that these sites are located on the external side of the membrane. However, clear-cut competition between H+ and Ca2+ could not be demonstrated with isolated sarcolemma.

Adenylyl Cyclases↗