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Biomedical subjects

E Holtzman

Publications and source records attributed to E Holtzman.

At least 55 records · Page 3Linked to original sources
PubMed1984

The effects of monensin on transport of membrane components in the frog retinal photoreceptor. I. Light microscopic autoradiography and biochemical analysis.

We have explored the use of the Na+-H+ ionophore monensin as a potential tool for the investigation of membrane assembly and transport in retinal photoreceptors. Autoradiographic analysis of frog retinas incubated with [3H]leucine in the presence of monensin revealed a lack of concentrated silver grains ("bands") at the base of the rod outer segments, in contrast to controls. This is indicative of a pronounced monensin-induced decrease in disc membrane assembly. Biochemical analyses of whole retinas and isolated rod outer segment membranes showed that protein synthesis (including opsin synthesis) was not significantly inhibited under these conditions, whereas passage of membrane protein to the rod outer segment was blocked. Glycerolipid synthesis was not significantly affected by monensin. The results suggest that membrane proteins (e.g., opsin) destined for incorporation into the rod outer segment must pass through the Golgi apparatus and demonstrate the potential utility of monensin for inhibiting aspects of marcomolecule transport in photoreceptors.

Animals↗
PubMed1984

The effects of monensin and of puromycin on transport of membrane components in the frog retinal photoreceptor. II. Electron microscopic autoradiography of proteins and glycerolipids.

Monensin converts the Golgi apparatus of rod photoreceptors into distended vacuoles, similar to those seen in other monensin-treated cell types, and leads to the accumulation of [3H]leucine in the distended vacuoles. As evaluated by quantitative, electron microscopic autoradiography, transport of newly made proteins--both to the outer segments and to the presynaptic terminals--is inhibited. These effects suggest that the Golgi apparatus is involved in transport in both principal directions within the highly polarized photoreceptors, a matter of interest since there seems to be only a single, extensive, Golgi apparatus in the cell body. Seemingly there are two distinguishable "sorting" routes, for proteins, out of the Golgi apparatus and, for the terminals, an additional non-Golgi route. Accumulation of newly made glycerolipids in the outer segments and terminals is less affected by monensin than is accumulation of new proteins, and glycerolipid accumulation is little affected by puromycin, an inhibitor of protein synthesis. These latter findings suggest that the routes or mechanisms of assembly of newly made lipids into membranes in the photoreceptors are at least partially dissociable from those for newly made proteins.

Animals↗
PubMed1983

The arrangement of the subunits of the acetylcholine receptor of Torpedo californica.

The monomeric form of the acetylcholine receptor from torpedo is composed of five, membrane-spanning chains with the stoichiometry alpha 2 beta gamma delta. The native receptor is predominantly a dimer cross-linked by a disulfide bridge between delta chains. We reduced native dimer to monomer and generated a different dimer by diamide-induced disulfide formation specifically between beta chains. Purified beta-beta cross-linked dimer, when adsorbed to a carbon film and negatively stained, appears in the electron microscope as two contiguous disks, frequently with central, stain-filled pits; i.e. it looks like native receptor in situ viewed normal to the plane of the membrane. We take the region of closest approach of the disks to mark the portions of the beta chains involved in the cross-link. In addition, we tagged the acetylcholine binding sites (one on each alpha chain) for electron microscopic identification, using a complex of monobiotinylated cobratoxin and avidin. Based on the locations of avidins bound to the beta-beta cross-linked dimer, the two toxin binding sites/monomer appear to be separated on the average by 110 degrees, as measured between lines from the center of the monomer to the centers of the avidins. One toxin binding site appears close to the beta-beta cross-link and the other close to the end of the monomer opposite to the cross-link; these locations are similar to the locations of the toxin binding sites relative to the delta-delta cross-link in native dimer. On the assumptions that the chains are compact units and are arranged in a unique order around the central pit, we interpret these results as indicating that the alpha chains are not contiguous and that neither the beta chain nor the delta chain lies between them. Therefore, the arrangement of the chains most easily reconciled with our assumptions and observations is alpha gamma alpha beta delta.

Animals↗
PubMed1983

Effects of monensin on photoreceptors of isolated frog retinas.

Monensin induces the vacuolization of the Golgi apparatus in photoreceptors of isolated frog retinas and also, more slowly, produces a vacuolization of the pre-synaptic terminals. Accompanying these effects is an inhibition of transport of protein to the outer segment so that the radioactive bands normally detectable by autoradiography do not form. Monensin thus promises to be a useful tool in the study of intracellular transport in photoreceptors. The findings reported here indicate that impairment of the functioning of the Golgi apparatus considerably diminishes transport of membrane protein to the rod outer segment suggesting that passage through the Golgi apparatus is an obligatory step for completion of outer segment membrane or its transport to the outer segment.

Animals↗
PubMed1983

Hyposplenism in systemic lupus erythematosus.

Hyposplenism, which is suggested by a typical peripheral blood smear and by the absence of splenic activity in a 99m Tc sulphur colloid scan, has been recently found to be associated with various diseases. This condition increases the susceptibility of patients to certain bacterial infections principally by pneumococci, meningococci and Haemophilus influenzae. The association of SLE and hyposplenism has not often been reported before; thus we see fit to report another such case. The administration of polyvalent pneumococcal vaccine is recommended in this condition.

Bacterial Vaccines↗
PubMed1983

Use of oral converting enzyme inhibitor, captopril for lateralizing renal venous renin activity.

Captopril was administered prior to renal vein renin sampling in an attempt to select patients amenable to surgical treatment for renin dependent hypertension. Renal venous blood for plasma renin activity was taken only after captopril stimulation. Sampling from the antecubital vein before and after this provocation showed a marked rise in renin, thereby confirming the efficacy of the test. Elimination of the initial selective renal vein sampling shortens the catheterization period without affecting the accuracy and dependability of the procedure.

Blood Pressure↗
PubMed1983

Hypertension in middle-aged men. Associated factors and mortality experience.

Seven hundred and seventeen hypertensive middle-aged men (HTs) were compared with 4,438 normotensive men (NTs). The association between the prevalence of hypertension and a number of demographic, physical, biochemical and electrocardiographic characteristics was examined by multiple logistic analysis. HTs were characterized by significant elevations of pulse rate, relative weight, serum uric acid, and high-density lipoprotein-cholesterol. HTs had a higher percent of major electrocardiographic findings, such as ischemic T wave changes, ST depression and, most significantly, left-ventricular hypertrophy. They were 4.7 yr older than the NTs and were more often of Central European than of Middle Eastern descent. Mortality in HTs over a 4.5-yr period was dose-response related to casual systolic and diastolic blood pressure readings at baseline. The age-adjusted HT/NT mortality ratio was approximately 2.5:1. Cardiovascular and cerebrovascular disease accounted for 69% of the total mortality among HTs as compared with 48% among NTs. The estimated mortality fraction attributable to hypertension was 23%. This figure provides an estimate for the goal of hypertension control in the community.

Adult↗
PubMed1982

Smooth endoplasmic reticulum and other agranular reticulum in frog retinal photoreceptors.

Frog retinal photoreceptors are favourable material for studying a number of unresolved issues concerning the interconnections, three-dimensional organization and functions of intracellular membrane systems in neurons. At least two distinct regions of smooth endoplasmic reticulum (SER) are present in these cells. One region, the subellipsoid SER, is located in rod cells at the base of the mitochondria-rich ellipsoid region, and is comprised of arrays of stacked tubules which exhibit frequent continuities with the rough endoplasmic reticulum (RER). The subellipsoid SER is also present throughout the ellipsoid region and at the apex of the inner segment. The second region of SER, the axonal SER, is comprised of agranular sacs and tubules present in the axons of rod cells, the perinuclear and Golgi regions of rod and cone cells and the synaptic terminals of rod and cone cells. There sacs and tubules exhibit continuities with cisternae of RER and with the nuclear envelope. Serial section analyses indicate that this SER can extend as a continuous networking along the entire length of the rod axons and throughout synaptic terminals. The axonal SER is distinct from the subellipsoid SER not only in location and morphology but also in its ability to bind divalent lead ions, a property it shares with synaptic vesicles, with agranular sacs at one face to the Golgi apparatus and with sacs extending from the Golgi apparatus toward the axons hillock. These latter sacs may serve in transport from the Golgi region to the axon. The axons SER in the axon, terminals, and the perinuculear and Golgi regions appear to be a source of synaptic vesicles as evidenced by this lead binding capacity and by the observation of vesicles, with the size (50-75 nm) and appearance of synaptic vesicles, budding from SER in direct continuity, with RER. The endoplasmic reticulum (ER) in synaptic terminals of frog photoreceptors is not continuous with endocytic structures found in the same region, such as blunt-ended tubules or anastomosing networks of tubules. Nor does the ER acquire exogenous horseradish peroxidase. These observations suggest that the ER does not play a direct role in membrane recycling in photoreceptors.

Animals↗
PubMed1982

Ultrastructural localization of glycerolipid synthesis in rod cells of the isolated frog retina.

The incorporation of two glycerolipid precursors, 3H-glycerol and 3H-choline, into rod cells of the isolated frog retina has been studied using quantitative electron microscope autoradiography. The results indicate that the endoplasmic reticulum (ER) is the major site of early incorporation of these precursors suggesting that the ER is the primary site of lipid synthesis. Of the different types of ER present in rod cells, the rough ER (RER) and nuclear envelope predominate in this activity. The organized region of smooth ER (SER) in the subellipsoid region does not appear to be of major quantitative importance, although SER closely intermingled with RER in the myoid region may be involved to some extent. We also compared the pattern of labelling observed at various incubation times in 3H-glycerol and 3H-choline with that observed with 3H-leucine. Differences were observed between the pattern of lipid and protein labelling, particularly in the labelling of the Golgi apparatus, mitochondria, plasma membrane, presynaptic terminals and outer segments. This suggests that lipids and proteins may differ in some aspects of the routes and mechanisms by which they are transported from their sites of synthesis to the membrane delimited compartments for which they are destined.

Animals↗
PubMed1982

Electron microscopy of complexes of isolated acetylcholine receptor, biotinyl-toxin, and avidin.

The principal curarimimetic toxin of Naja naja siamensis derivatized with biotinyl groups binds specifically both to acetylcholine receptor, isolated from Torpedo californica electric tissue, and to avidin. Isolated complexes of receptor monomer or dimer, biotinyl-toxin, and avidin were negatively stained and examined in the scanning transmission electron microscope. We measured the angle made by the radius of each avidin bound at the periphery of a monomeric unit in dimer to the axis connecting the centers of the monomers, starting at the crosslink between the monomers. We infer from the distribution of these angles that one toxin binding site is located in the range of 45 degrees to 85 degrees and another at about 100 degrees further from the crosslink between the monomers. Because it is known that there are two toxin binding sites per monomer, associated with the two alpha chains, the bound avidins presumably point to portions of the alpha chains, indicating their positions relative to that portion of the delta chain located at the crosslink between monomers in dimer.

Animals↗
PubMed1982

Effect of barium and tetraethylammonium on membrane circulation in frog retinal photoreceptors.

We studied the influence of altered ionic conditions on the recycling of synaptic vesicle membrane in frog retinal photoreceptors using horseradish peroxidase to monitor synaptic activity and trace the fate of internalized membrane. The addition of 1.2 mM barium or 20 mM tetraethylammonium to isolated retinas maintained in Ringer's solution, changes the usual balance of membrane circulation in the rod cells; the cone cells are much less affected. Retrieval of synaptic vesicle membrane in the rods, which normally regenerates small vesicles, becomes mediated predominantly by large sacs and vacuoles ("cisternae"). Because these cisternae can be labeled with peroxidase, they appear to arise from endocytized membrane. Morphometric analysis suggests strongly that the cisternae are formed of circulating synaptic vesicle membrane. The effects of barium and tetraethylammonium can be inhibited by high extracellular potassium, by high intensity light, and by 5 mM cobalt. They seem likely to depend on potassium channels, though additional more complex mediation may also be involved. The alterations in membrane retrieval that we find are of interest in terms of the multiple pathways of membrane cycling now being uncovered. They open potential experimental approaches to the controls of this circulation. In addition, the findings extend our previous ones demonstrating that rod cells and cone cells differ in their responses to divalent cations in ways that seem likely to be of physiological importance.

Animals↗
PubMed1982

Angiotensin-I converting enzyme activity in the sera of captopril-treated hypertensive patients.

The blood pressure and serum angiotensin-I converting enzyme (SACE) activity were measured in captopril-treated hypertensive patients at frequent intervals. Inhibition of SACE was observed in patients responding to the treatment with lowering of blood pressure as well as in nonresponding cases. It was therefore concluded that a mechanism not depending on the formation of angiotensin-II by ACE is responsible for the high blood pressure persisting in the captopril treated nonresponding hypertensive patients. SACE activity in sera of captopril-treated patients recovers from inhibition when stored in frozen state at -20 degrees c. An apparent dissociation was therefore observed when regeneration of SACE activity during storage of sera was not taken into account. Meaningful activities are therefore obtained only if the assay is performed without prolonged storage.

Adult↗
PubMed1982

Captopril, an orally active angiotensin I converting enzyme inhibitor in the treatment of renovascular and essential hypertension.

The hypotensive response to captopril is described for 12 hypertensive patients, 7 of whom had renovascular hypertension. The drug was effective in lowering blood pressure. The few reversible adverse reactions that occurred included loss of the sense of taste in one patient and rash and fever in another. Three patients with renal failure showed deterioration of renal function during treatment, suggesting the advisability of treating such cases with lower dosages.

Adult↗