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Biomedical subjects

J Horwitz

Publications and source records attributed to J Horwitz.

At least 127 records · Page 7Linked to original sources
PubMed1986

Comparison of the effects of muscarine and vasopressin on inositol phospholipid metabolism in the superior cervical ganglion of the rat.

Both muscarine and vasopressin have been shown previously to increase the accumulation [3H]inositol phosphates in superior cervical ganglia in which the phospholipids were labeled with [3H] inositol. In this study, we have compared the effects of muscarine and of vasopressin on phospholipid metabolism in the ganglion. The effects of these agents on [3H]inositol phosphate accumulation are additive. The response to muscarine levels off after approximately 10 min, whereas the response to vasopressin increases for at least 30 min. The incorporation of [3H]inositol into phospholipids is enhanced in decentralized ganglia and in ganglia maintained in organ culture compared to freshly isolated ganglia. These treatments appear to potentiate the effect of muscarine on [3H]inositol phosphate accumulation, but do not affect the response of the ganglia to vasopressin. Muscarine and vasopressin also increase the incorporation of [3H]inositol into phospholipids in the ganglion. Autoradiographic techniques were used to localize the inositol-containing phospholipids in the ganglion. Muscarine increases phospholipid labeling primarily in the cell bodies of the principal ganglionic neurons, whereas vasopressin increases phospholipid labeling primarily in the neuropil. These data are consistent with the hypothesis that muscarine and vasopressin stimulate the hydrolysis of different pools of ganglionic phospholipids.

Animals↗
PubMed1986

Melatonin-binding in the frog retina: autoradiographic and biochemical analysis.

Binding of melatonin was examined in the retina of Rana pipiens. When intact frog retinas were incubated with 3H-melatonin and processed for autoradiography, most of the radioactivity was localized to the melanosomes of the retinal pigment epithelium-choroid (RPE-choroid) and to the outer plexiform layer of the retina. Melanosome-enriched fractions of the RPE-choroid and membrane-enriched fractions of the neural retina demonstrated saturable melatonin binding when incubated with increasing melatonin concentration. Thin-layer chromatography showed that greater than 98% of the bound radioactivity was authentic melatonin. Scatchard analysis revealed a single population of binding sites with apparent Kd values of 6 X 10(-7) M for both the RPE-choroid and neural retina. When various indole analogs were tested for their ability to inhibit 3H-melatonin binding to the neural retina, both 5-methoxytryptophol and 6-chloromelatonin demonstrated complete displacement of melatonin binding. Endogenous retinal melatonin levels were measured by radioimmunoassay. A twofold increase in melatonin levels was observed during the dark period with peak levels at 384.5 +/- 28.8 pgms melatonin/pair retinas. Melatonin levels persisted in constant darkness, but were suppressed in constant light. Our data suggest that in the frog, the sites of action of retinal melatonin are the melanosomes of the RPE-choroid and the outer plexiform layer of the neural retina.

Animals↗
PubMed1986

Covalent changes in MIP26K during aging of the human lens membrane.

Rabbit antisera have been made to the C-terminal octapeptide of bovine MIP26K (residues 256-263) and to an octapeptide near the C-terminus (residues 252-259). Use of these antisera in Western blot analysis of membrane from young vs old human lenses, and from cortex vs nucleus of old human lenses, suggest age-related covalent changes in the C-terminus of MIP26K. These age-related changes in anti-256-263 and anti-252-259 sera can be mimicked by treatment of lens membrane with carboxypeptidase Y, suggesting the loss of 1-8 amino acid residues from the C-terminus of the 26,000 dalton form of MIP26K during aging of the normal human lens.

Aging↗
PubMed1985

Vasoactive intestinal peptide increases tyrosine hydroxylase activity in normal and neoplastic rat chromaffin cell cultures.

Vasoactive intestinal peptide (VIP) acutely increases tyrosine hydroxylase (TH) activity in cultures of dispersed normal adult rat chromaffin cells and of PC12 rat pheochromocytoma cells. High concentrations of VIP (10 microM) produce about 3-fold increases in TH activity in both cell types. VIP also increases the content of cyclic adenosine 3':5'-monophosphate (cAMP) in PC12 cells. VIP may increase TH activity by promoting the cAMP-dependent phosphorylation of the enzyme. Nerve fibers containing VIP-like immunoreactive material have been reported in the adrenal medulla and in other catecholamine (CA)- storing tissues. This VIPergic innervation may regulate CA synthesis and other cAMP-dependent processes in these tissues.

Adrenal Gland Neoplasms↗
PubMed1985

Immunohistochemical and biochemical detection of serotonin in the guinea pig celiac-superior mesenteric plexus.

Serotonin (5-HT) in the guinea pig celiac-superior mesenteric plexus was quantitatively measured by HPLC and visualized by an immunohistochemical method. Preincubation of the ganglia in a Krebs solution containing L-tryptophan and pargyline markedly elevated the content of 5-HT and K+ solution caused a release of 5-HT into the incubation medium. 5-HT immunoreactivity was localized to dense but unevenly distributed nerve fibers throughout the plexus and to small diameter cells commonly referred to as small intensely fluorescent cells. These findings provide evidence of an extensive network of 5-HT-containing neural elements in the guinea pig prevertebral ganglia.

Animals↗
PubMed1985

The visual pigment sensitivity hypothesis: further evidence from fishes of varying habitats.

Visual pigments were extracted from the retinas of 8 species of marine teleosts and 4 species of elasmobranchs and a comparison was made of the pigment properties from these fishes, some inhabiting surface waters, others from the mesopelagic zone, and a few migrating vertically between these two environments. An association was found between the spectral position of the absorbance curve and the habitat depth or habitat behavior, with the blue-shifted chrysopsins being the pigments of the twilight zone fishes and the rhodopsins with fishes living near the surface. The retina of the swell shark (Cephaloscyllium ventriosum) yielded extracts with two photopigments; one, a rhodopsin at 498 nm; the second, a chrysopsin at 478 nm. This fish has been reported to practice seasonal vertical migrations between the surface and the mesopelagic waters. In addition to the spectral absorbance, several properties of these visual pigments were examined, including the meta-III product of photic bleaching, regeneration with added 11-cis and 9-cis retinals, and the chromophoric photosensitivity. The chrysopsin properties were found to be fundamentally similar to those of typical vertebrate rhodopsins. Correlating the spectral data with the habitat and habitat behavior of our fishes gives us confidence in the idea that the scotopic pigments have evolved as adaptations to those aspects of their color environment that are critical to the survival of the species.

Animals↗
PubMed1985

Characterization of polypeptides from human nuclear cataracts by Western blot analysis.

Water-soluble and water-insoluble polypeptides from nuclei of clear vs. opaque and brunescent human lenses were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophoretically transferred to nitrocellulose paper. Treatment of the nitrocellulose blots with monospecific antisera to human alpha and beta crystallin and to antisera against the Major Intrinsic Polypeptide (MIP26) of lens membrane demonstrated no difference in binding between microdissected sections of clear vs. opaque (and brunescent) nuclei. In contrast, treatment of nitrocellulose blots with monospecific antisera to human gamma crystallin demonstrated little or no binding to polypeptides from opaque (and brunescent) nuclei as compared with age-matched clear nuclei. These results demonstrate the selective involvement of gamma crystallins in opacification (and brunescence) in the human lens nucleus, and strongly suggest the presence of covalent changes of the gamma crystallin molecule during development of the human nuclear cataract.

Aged↗
PubMed1985

tau-Crystallin from the turtle lens: purification and partial characterization.

A lens protein with a molecular mass near 46 000 daltons has been purified from the turtle lens. It is a monomeric protein which differs from other lens crystallins in its antigenicity, near-UV circular dichroism spectrum and amino acid composition. Like delta-crystallin, it has appreciable secondary structure (52% alpha-helix). This lens protein has been named tau-crystallin. tau-Crystallin cross-reacts with the novel 48 000 dalton protein identified recently in lenses of the sea lamprey. Although distinct, the possibility that tau-crystallin shares an ancestral relationship with delta-crystallin is discussed.

Amino Acids↗
PubMed1985

Spatial and temporal mapping of the age-related changes in human lens crystallins.

Using the techniques of high performance liquid chromatography (HPLC), gel electrophoresis in the presence of sodium dodecyl sulfate (SDS), and immunoblotting, we have analyzed the age-related changes in soluble crystallins of the human lens. A 3 mm core along the optical axis of each lens was frozen-sectioned and the sections were biochemically analyzed for distribution and quantity of the various soluble protein species. Both cortical and nuclear samples show a monotonic decrease in the concentration of the 19 000 and 21 000 MW proteins with age. We find that these proteins behave anomalously on SDS-polyacrylamide gels, running near the top of the gel when the samples are not boiled before loading; this permitted us to observe the gradual, age-related loss of these bands from the gels of both nuclear and cortical samples. The high molecular weight, or TSK-3000 void volume, fraction (greater than 350,000) of the cortex contained alpha crystallin at all ages. However, in the nucleus, while this fraction is primarily composed of alpha crystallin early in life (i.e. before 15 years of age), there is a gradual incorporation of other crystallins into the void volume. This change in the composition of the high-molecular-weight, soluble protein fraction is reflected in: a change in the subunit mobility on SDS-polyacrylamide gels; reactivity of the fraction to crystallin antibodies, i.e. in the young nucleus there is reactivity to anti-alpha crystallin only, with a gradual increase in reactivity to anti-beta and anti-gamma crystallins. The void volume fraction of the nucleus persists as a major component of the soluble protein pool until 42-44 years of age, at which time the proportion of the total soluble protein represented by this void volume fraction decreases precipitously. These changes in the soluble protein profile are discussed in terms of their potential influence on the functioning of the lens.

Adolescent↗
PubMed1985

Antisera to synthetic peptides of lens MIP26K (major intrinsic polypeptide): characterization and use as site-specific probes of membrane changes in the aging human lens.

Based upon the amino acid sequence of bovine lens MIP26K obtained from cDNA cloning (Gorin, Yancey, Cline, Revel and Horwitz, 1984), two octapeptides (amino acid nos 252-259, 240-247) near the C-terminus have been synthesized. Rabbit antisera to these peptides recognize the intact MIP26K molecule from bovine, human and chick lens membrane. When compared with rabbit antisera to intact MIP26K or to its major cyanogen bromide fragment (CB-1), the antiserum to the sequence 252-259 was able to recognize age-related changes in human MIP26K not detectable by the conventional anti-MIP26K or anti-CB-1 sera.

Adult↗
PubMed1985

Low-Na+ medium increases the activity and the phosphorylation of tyrosine hydroxylase in the superior cervical ganglion of the rat.

Incubation of the rat superior cervical ganglion in Na+-free or low-Na+ medium increased the rate of synthesis of 3,4-dihydroxyphenylalanine (DOPA) in the ganglion fourfold and caused a concomitant stable activation of tyrosine hydroxylase. DOPA synthesis was half-maximal in medium containing about 20 mM Na+. Low-Na+ medium also increased the incorporation of 32Pi into tyrosine hydroxylase; the dependence of tyrosine hydroxylase phosphorylation on the Na+ concentration resembled that of DOPA synthesis. The stimulatory effects of low-Na+ medium on DOPA production and on tyrosine hydroxylase activity in vitro were dependent on extra-cellular Ca2+. The stimulation of DOPA synthesis in low-Na+ medium was inhibited by methoxyverapamil, an inhibitor of Ca2+ uptake, and was partially blocked by tetrodotoxin, but it was not affected by the cholinergic antagonists hexamethonium and atropine. Ionomycin, a calcium ionophore, stimulated DOPA synthesis to about the same extent as low-Na+ medium and also increased the incorporation of 32Pi into tyrosine hydroxylase. 8-Bromo cyclic AMP (1 mM) also stimulated DOPA production in the ganglion, and this stimulation was more than additive with that produced by low-Na+ medium. These data support the hypothesis that low-Na+ medium stimulates DOPA synthesis by raising intracellular Ca2+, which then promotes the phosphorylation of tyrosine hydroxylase.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1985

Effects of neuronal activity on inositol phospholipid metabolism in the rat autonomic nervous system.

The effect of nerve stimulation on inositol phospholipid hydrolysis in autonomic tissue was assessed by direct measurement of [3H]inositol phosphate production in ganglia that had been preincubated with [3H]inositol. Within minutes, stimulation of the preganglionic nerve increased the [3H]inositol phosphate content of the superior cervical sympathetic ganglion indicating increased hydrolysis of inositol phospholipids. This effect was blocked in a low Ca2+, high Mg2+ medium. It was also greatly reduced when nicotinic and muscarinic antagonists were present together in normal medium. However, neither the nicotinic antagonist nor the muscarinic antagonist alone appeared to be as effective as both in combination. In other experiments, stimulation of the vagus nerve caused dramatic increases in [3H]inositol phosphate in the nodose ganglion but did not increase [3H]inositol phosphate in the nerve itself. This effect was insensitive to the cholinergic antagonists. Thus, neuronal activity increased inositol phospholipid hydrolysis in a sympathetic ganglion rich in synapses, as well as in a sensory ganglion that contains few synapses. In the sympathetic ganglion, synaptic stimulation activated inositol phospholipid hydrolysis and this was primarily due to cholinergic transmission; both nicotinic and muscarinic pathways appeared to be involved.

Animals↗
PubMed1985

The distribution of the main intrinsic membrane polypeptide in ocular lens.

The Main Intrinsic Polypeptide (MIP) of the ocular lens fiber cell plasma membrane was immunocytochemically localized at the ultrastructural level on ultrathin frozen sections of rat lens, and on extracted, gradient-purified bovine lens membranes. The results indicate that both the junctional and non-junctional membrane domains of the cortical lens fiber cell are MIP immunoreactive. Frozen thin section immunocytochemistry of the lens epithelium and hepatocytes, also using anti-MIP antibodies, revealed that these cells, and their intercellular junctions, are not MIP-immunoreactive. From these findings we conclude that 1) MIP, a putative fiber cell junctional protein, is present throughout the plasma membrane of the lens fiber cell, and is not confined to the fiber cell junctional domain, 2) MIP is not a detectable component of the lens epithelial cell membrane, or its intercellular junctions, 3) MIP is not detectable in gap junctions of hepatocytes.

Animals↗
PubMed1985

Aging-related cataract: laboratory investigation and clinical management.

Cataract disrupts the crystalline lens, a transparent, elastic, avascular, biconvex structure composed of a capsule, lens epithelium, and lens fiber cells. Many factors contribute to the progression of lens opacity, but aging is most frequently associated with cataract. As aging-related cataract develops, many biochemical and biophysical changes occur, most notably a marked increase in the insolubilization of the crystallin and extensive oxidation damage to many of the lens constituents. Cataract management should include ophthalmologic history and examination, medical evaluation, optical correction, control of ocular and systemic disease that may contribute to cataract, discontinuation of cataractogenic drugs, and periodic reexamination. Surgery is indicated when cataract is associated with vision decrease interfering with activities important to the patient, intraocular inflammation or glaucoma, or interference with management of posterior segment disease. More than 600 000 cataract operations are done in the United States each year; in 1982 an estimated 496 000 cataract operations were combined with intraocular lens implantation.

Aged↗
PubMed1985

Muscarine stimulates the hydrolysis of inositol-containing phospholipids in the superior cervical ganglion.

Previous studies have shown that muscarine increases the incorporation of 32Pi and [3H]inositol into phosphatidylinositol in the superior cervical ganglion of the rat. Because the first event in agonist-stimulated phospholipid turnover is thought to be the hydrolysis of phosphatidylinositol or of phosphatidylinositol phosphates, we measured the accumulation of [3H]inositol phosphates in ganglia in which these lipids had been labeled by preincubation with [3H]inositol. The production of [3H]inositol phosphates under these conditions presumably reflects the activity of a phospholipase C in the ganglion. Muscarine caused a large increase in the formation of [3H]inositol phosphates. Most of this increase was in the form of [3H]inositol-1-phosphate. The stimulation of [3H]inositol phosphate accumulation by muscarine was not dependent upon the presence of extracellular Ca++. Agents that increase Ca++ influx caused only a small increase in the accumulation of [3H]inositol phosphates. We also measured the formation of [3H]inositol phosphates in extracts of the ganglion. These extracts contained a phospholipase C activity that was stimulated by deoxycholate and that hydrolyzed phosphatidylinositol phosphates more actively than phosphatidylinositol. This phospholipase C activity was Ca++-dependent. We propose that muscarine may activate this phospholipase C in the intact ganglion and that muscarine increases phospholipase C activity by some mechanism other than by increasing the influx of Ca++.

Animals↗
PubMed1985

Localization of hydroxyindole-O-methyltransferase in the mammalian pineal gland and retina.

The pineal hormone, melatonin, has been reported to be synthesized in the retina by the enzyme, hydroxyindole-O-methyltransferase (HIOMT). Several laboratories have suggested that melatonin may be involved in photoreceptor outer segment disc shedding, photomechanical movements, and neuromodulation, but the cellular location of the retinal synthesizing enzymes has not been determined yet. Antiserum to HIOMT was obtained from rabbits immunized with bovine pineal extract. The monospecific immunoglobulins to HIOMT were isolated by positive-negative selection using pineal extract-sepharose and brain extract-sepharose affinity chromatography. The purity and specificity of the antibody to HIOMT was confirmed by immunodiffusion, electroblot immunolabeling, SDS-PAGE, and immunoprecipitin titration. Using the peroxidase-antiperoxidase (PAP) technique, HIOMT was localized in the pinealocytes of bovine and human pineal glands obtained during the light period. Rat pineal glands obtained during the dark period exhibited HIOMT immunoreactivity, whereas rat pineal glands obtained during the light period did not. Some pinealocytes of the bovine pineal did not exhibit HIOMT immunoreactivity, suggesting that not all pinealocytes are actively involved in melatonin synthesis. HIOMT was localized in the photoreceptors of bovine, rat, and human retinas, and some labeling also was observed in the inner retina, although the latter showed some species variation. This observation supports the hypothesis that photoreceptors are capable of melatonin synthesis.

Acetylserotonin O-Methyltransferase↗