Structural alterations of tapetal cells in the retina of cats induced by prolonged treatment with chloroquine

Summary Cats were treated with high doses of chloroquine for one year during which the ocular fundus was periodically examined. After completion of the treatment, the tapetal cells were investigated by light and electron microscopy. Prolonged treatment with the retinotoxic drug chloroquine reduced the light reflection of the fundus, and examination by light and electron microscopy revealed a destruction of the rod-like structures in the cytoplasm of the tapetal cells.     

The structure and distribution of satellite cells of cardiac muscles in decapod crustaceans

Summary The structure and distribution of satellite cells of cardiac muscles were examined in twenty-one species of animals chosen from each tribe within the order Decapoda (Arthropoda, Crustacea). The satellite cells were found in all animals observed. Most of them are morphologically identical with those described in different striated muscles of other species, but some cells have unusual features. The decapod satellite cell occasionally lies right over the region corresponding to the intercalated disc between the apposed cardiac muscle cells. The cell sends cytoplasmic processes into the adjacent muscle cells, enabling the plasma membrane to make close contact with the cleft opening of the intercalated disc, and with the myofibril at the level of the Z-line. Another characteristic feature is the presence of paired cells. Such cells are clearly separated from each other over most of the contact area by the respective plasma membranes, which are smooth in appearance and devoid of specialized regions. The significance of the presence of satellite cells in decapod cardiac muscle and its possible role are discussed and compared with those described for other species.     

Fine structure of Merkel cells in lampreys

Summary The structure of Merkel cells occurring in the epidermis of adult and larval stages of Lampetra spp. is described; it is comparable to that reported from the gnathostome classes. The cells bear microvilli, grouped on the distal and proximal aspects, and are associated with sparsely branching and varicose nerve fibres. One branch of the neurite bears a spur-like process which indents the proximal side of the Merkel cell. Most of the specific Merkel granules are situated in the vicinity of this neurite projection; the cell membrane adjacent to the tip of the spur process bears structures resembling presynaptic densities. Occasionally, desmosome-like junctions are found between the neurite and the Merkel cell.The authors thank the Fresh Water Biological Association and the Department of Biological Sciences, University of Bath, for supplying the material, Dr. H. Fox for giving some prepared blocks of Lampetra planeri adults, Mr. B.L. Pirie for technical assistance, and the Science Research Council for support through grant GR/A/3740.6     

Induction by progesterone of a sexual dimorphism of estrogen uptake by anterior pituitary cells in situ

Summary The effects of progesterone pretreatment on in vivo ³H-estrogen uptake by five anterior pituitary cell types was analyzed by means of a quantitative autoradiographic-immunocytochemical technique. Male and female rats castrated for 14 days show nuclear concentration of label in all five cell types one h after injection of ³H-estradiol, whether progesterone treated or not. The order of labeling intensity is gonadotropes lactotropes = somatotropes > thyrotropes = corticotropes. Progesterone treatment induces a dramatic sexual dimorphism in estrogen uptake; it significantly increases ³H-estrogen uptake in all female cell types. In males, progesterone decreases uptake in gonadotropes while not altering uptake in other cell types.Supported by PHS grant HD 12173 and Research Career Development Award HD 00243. Portions of these data were presented at the American Association of Anatomists meeting, Omaha, 1980I wish to acknowledge Mr. Sing Kung Lau for his excellent technical assistance and Dr. P. Rodier for her advice and assistance with the statistical analyses. I also wish to thank Dr. A.F. Parlow and NIAMDD for antisera against rLH, hFSH, rPRL and rTSH and Dr. Peter Petrusz, University of North Carolina, for antisera against bGH and h endorphin     

Observations on the marginal ruffles of an established fibroblast-like cell line

Summary LW13K2 cells, a clone of a spontaneously in vitro transformed derivative of embryonic Lewis rat fibroblastic cells, were studied by phase contrast cine-light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ruffles found at the advancing edge of cells grown on glass substrates in vitro form and recede in a period of less than one min if they do not make an attachment of the substrate. If they fail to make an attachment they may form pinocytotic channels near the leading edge as described by Price (1972) and/or collapse, generally backwards, towards the cell body. The spines which appear to reinforce the membranous ruffles are the last structures to disappear, and accumulate in an irregular array behind the ruffling edge; this area is behind that in which pinocytosis occurs. In comparison with the sparse numbers of ribosomes found in the trailing edge, they are present in notable concentrations near the leading, ruffling edge of the cell. No membrane vesicles have been found in or near the ruffling edges at the ruffle-spine concentration zone.     

Tubular extensions of the plasmalemma in leaf cells of Zea mays L.

Leaf tissues of Zea mays were examined with a transmission electron microscope and a high-voltage electron microscope. Tubular extensions (invaginations) of the plasmalemma were found in vascular parenchyma cells and thick-walled, lateformed sieve elements of intermediate and small veins, and in epidermal, mesophyll, and sheath cells of all leaves examined. No continuity seems to exist between the tubules and other cellular membranes.     

Inositol 1,4,5-Trisphosphate 3-Kinase mRNA: High Levels in the Rat Hippocampal CA1 Pyramidal and Dentate Gyrus Granule Cells and in Cerebellar Purkinje Cells

The distribution of inositol 1,4,5-trisphosphate (InsP3) 3-kinase mRNA in the rat brain is reported using oligonucleotides based on a cDNA clone sequence that encodes rat brain InsP3 3-kinase and the in situ hybridization technique. Moderate levels were found in CA2-4 pyramidal neurons, in the cortex, and in the striatum. The cerebellar granule cells, thalamus, hypothalamus, brainstem, spinal cord, and white matter tracts were almost negative. The levels of InsP3 3-kinase mRNA were highest in the hippocampal CA1 pyramidal neurons, granule cells of the dentate gyrus, and cerebellar Purkinje cells. These results contrast with the lower concentration of the InsP3 receptor already reported in the hippocampus versus the Purkinje cells and suggest a special role for inositol 1,3,4,5-tetrakisphosphate in Ammon's horn.     

Enhancement by Cytidine of Membrane Phospholipid Synthesis

Cytidine, as cytidine 5'-diphosphate choline, is a major precursor in the synthesis of phosphatidylcholine in cell membranes. In the present study, we examined the relationships between extracellular levels of cytidine, the conversion of [14C]choline to [14C]phosphatidylcholine, and the net syntheses of phosphatidylcholine and phosphatidylethanolamine by PC12 cells. The rate at which cytidine (as [3H]cytidine) was incorporated into the PC12 cells followed normal Michaelis-Menten kinetics (Km = 5 microM; Vmax = 12 x 10(-3) mmol/mg of protein/min) when the cytidine concentrations in the medium were below 50 microM; at higher concentrations, intracellular [3H]cytidine nucleotide levels increased linearly. Once inside the cell, cytidine was converted mainly into cytidine triphosphate. In pulse-chase experiments, addition of cytidine to the medium caused a time- and dose-dependent increase (by up to 30%) in the incorporation of [14C]choline into membrane [14C]-phosphatidylcholine. When the PC12 cells were supplemented with both cytidine and choline for 14 h, small but significant elevations (p less than 0.05) were observed in their absolute contents of membrane phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine, all increasing by 10-15% relative to their levels in cells incubated with choline alone. Exogenous cytidine, acting via cytidine triphosphate, can thus affect the synthesis and levels of cell membrane phospholipids.     

Lan-1: A Human Neuroblastoma Cell Line With M1 and M3 Muscarinic Receptor Subtypes Coupled to Intracellular Ca2+ Elevation and Lacking Ca2+ Channels Activated by Membrane Depolarization

The LAN-1 clone, a cell line derived from a human neuroblastoma, possesses muscarinic receptors. The stimulation of these receptors with increasing concentrations of carbachol (CCh; 1-1,000 microM) caused a dose-dependent increase of the intracellular free Ca2+ concentration ([Ca2+]i). This increase was characterized by an early peak phase (10 s) and a late plateau phase. The removal of extracellular Ca2+ reduced the magnitude of the peak phase to approximately 70% but completely abolished the plateau phase. The muscarinic-activated Ca2+ channel was gadolinium (Gd3+) blockade and nimodipine and omega-conotoxin insensitive. In addition, membrane depolarization did not cause any increase in [Ca2+]i. The CCh-induced [Ca2+]i elevation was concentration-dependently inhibited by pirenzepine and 4-diphenylacetoxy-N-methylpiperidine methiodide, two rather selective antagonists of M1 and M3 muscarinic receptor subtypes, respectively, whereas methoctramine, an M2 antagonist, was ineffective. The coupling of M1 and M3 receptor activation with [Ca2+]i elevation does not seem to be mediated by a pertussis toxin-sensitive guanine nucleotide-binding protein or by the diacylglycerol-protein kinase C system. The mobilization of [Ca2+]i elicited by M1 and M3 muscarinic receptor stimulation seems to be dependent on an inositol trisphosphate-sensitive intracellular store. In addition, ryanodine did not prevent CCh-induced [Ca2+]i mobilization, and, finally, LAN-1 cells appear to lack caffeine-sensitive Ca2+ stores, because the methylxanthine was unable to elicit intracellular Ca2+ mobilization, under basal conditions, after a subthreshold concentration of CCh (0.3 microM), or after thapsigargin.     

Opioid Signal Transduction in Intact and Fragmented SH-SY5Y Neural Cells

Parameters of ligand binding, stimulation of low-Km GTPase, and inhibition of adenylate cyclase were determined in intact human neuroblastoma SH-SY5Y cells and in their isolated membranes, both suspended in identical physiological buffer medium. In cells, the mu-selective opioid agonist [3H]Tyr-D-Ala-Gly(Me)Phe-Gly-ol ([3H]DAMGO) bound to two populations of sites with KD values of 3.9 and 160 nM, with less than 10% of the sites in the high-affinity state. Both sites were also detected at 4 degrees C and were displaced by various opioids, including quaternary naltrexone. The opioid antagonist [3H]naltrexone bound to a single population of sites, and in cells treated with pertussis toxin the biphasic displacement of [3H]naltrexone by DAMGO became monophasic with only low-affinity binding present. The toxin specifically reduced high-affinity agonist binding but had no effect on the binding of [3H]naltrexone. In isolated membranes, both agonist and antagonist bound to a single population of receptor sites with affinities similar to that of the high-affinity binding component in cells. Addition of GTP to membranes reduced the Bmax for [3H]DAMGO by 87% and induced a linear ligand binding component; a low-affinity binding site, however, could not be saturated. Compared with results obtained with membranes suspended in Tris buffer, agonist binding, including both receptor density and affinity, in the physiological medium was attenuated. The results suggest that high-affinity opioid agonist binding represents the ligand-receptor-guanine nucleotide binding protein (G protein) complex present in cells at low density due to modulation by endogenous GTP.(ABSTRACT TRUNCATED AT 250 WORDS)