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At least 829 records · Page 46Linked to original sources
PubMed1981

Immunocytochemical localization of fibronectin in limb tissues of the adult newt, Notophthalmus viridescens.

This study describes the immunocytochemical localization of fibronectin, a defined connective tissue and plasma glycoprotein, and its relationship to collagen and reticulin in adult newt limb tissues. We have also isolated the plasma form of fibronectin in a related species, the adult mudpuppy. The insoluble form of fibronectin was detected with immunoperoxidase stain in basement membranes and loose connective tissue. The endoneurium and perineurium of nerve bundles and the connective tissue elements of striated muscle stained heavily for fibronectin. The dermis and blood vessel walls also reached positively with the immunoperoxidase stain. A similar distribution was observed for reticulin with conventional histologic techniques with the exception of the dermis where only trace amounts of the protein were observed. Fibronectin and collagen were codistributed in the tissues studies. Fibronectin appeared to be intercalated among larger collagenous fibers. Collagen and fibronectin form an extracellular connective tissue scaffold that abuts against many types of adherent cells in different tissues. This supports the possible role of fibronectin in cell-matrix interactions and normal cell and tissue organization.

Animals↗
PubMed1984

Retinal carbonic anhydrase: a comparative study.

Activity levels of carbonic anhydrase (E.C. 4.2.1.1) were measured in the retina and pigment epithelium of thirteen vertebrate species. The animals cover five taxonomic classes and among them illustrate four different retinal vascular supply patterns. The species can also be grouped according to their temperature regulatory mechanisms; i.e., homeothermic or poikilothermic. Significant differences are observed when the enzyme activities are examined by taxonomic class-birds and reptiles appear to have very high levels of enzyme activity; mammals and fish, moderate levels; and amphibia, low levels. When the enzyme activities are regrouped according to either vascular structure or temperature regulation, no significant differences are observed. From this, it is concluded that the level of carbonic anhydrase required by retinal tissue is not directly related to either of these factors. Carbonic anhydrase activity in kidney was compared with that in retina/pigment epithelium. Retina/pigment epithelium values are as great or greater than those in kidney but show a wider range. Only mammalian and avian kidney CA activity levels are high. We suggest that carbonic anhydrase levels in retina/pigment epithelium may be responsive to factors which influence vitreo-retinal ion and pH gradients.

Animals↗
PubMed1991

Probing the structure and function of the nuclear pore complex.

Nucleocytoplasmic transport is a bi-directional process mediated by the nuclear pore complex (NPC), which results in a segregation of cytoplasmic and nuclear macromolecules within cells. Some progress has been made in understanding the mechanistic basis of this selective transport phenomenon. In particular, cryo-electron microscopy of frozen-hydrated nuclear envelopes coupled with image processing and labeling studies, has provided a glimpse of the transporter at the center of the NPC.

Amino Acid Sequence↗
PubMed1990

Regulation of renal proximal tubule basolateral potassium channels.

In summary, these studies report a voltage-gated, stretch-activated K channel at the basolateral membrane of amphibian proximal tubule. In the normal range of potential, any reduction in metabolic activity leading to membrane depolarization would reduce the open-probability of the basolateral K channel, thereby preventing excessive loss of K out of the cell. This type of voltage gating is consistent with the decrease in macroscopic K conductance observed in perfused frog tubules after cell depolarization (Messner et al., 1985). However, it does not account for the delayed increase in basolateral K conductance that accompanies Na-substrate cotransport across the apical membrane. The stretch-activation property of basolateral K channels may explain both electrolyte and volume homeostasis in the amphibian proximal tubule. Na-substrate cotransport produces a gradual increase in cell volume in several preparations (Hempling and Hare 1961; Hacking and Eddy 1981; Hudson and Schultz 1988;). Hence, the observed increase in K conductance during luminal addition of Na-cotransported substrates may be mediated by small changes in cell volume. For example, a stretch-activated K channel, stimulated by a 1% increase in cell volume, would allow K to exit the cell down its electrochemical gradient, thereby balancing the increased K uptake associated with greater Na pump activity. A number of studies have provided evidence that cell swelling increases macroscopic K conductance (Davis and Finn 1982; Germann et al. 1986; Grinstein et al. 1982; Grinstein et al. 1984; Hamill 1983; Hoffmann 1985; Lau et al. 1984; Lopes and Guggino 1987; Richards and Dawson 1986) as well as chloride channel activity (Hudson and Schultz 1988). However, the present study is the first to suggest that the swelling-induced increase in basolateral K conductance results from stretch-activated K channels. This same stretch-activation property may also be involved in the VRD that occurs during exposure of proximal tubule cells to hypotonic media (Dellesaga and Grantham 1973; Welling et al. 1985; Lopes and Guggino 1987; Kirk et al 1987). Since cell swelling undoubtably increases membrane tension (Kelly and Macklem 1988), swollen amphibian proximal tubule cells would lose K because of an increase in the open probability of stretch-activated K channels. The additional exit of bicarbonate and water would restore the cells to their original volume.

Animals↗
PubMed1988

Do N-methyl-D-aspartate receptors mediate synaptic responses in the mudpuppy retina?

Whole-cell recordings of amacrine and ganglion cells in the superfused retina-eyecup preparation of the mudpuppy were obtained in order to determine which excitatory amino acid receptor (EAAR) subtype mediates the synaptic responses of these neurons. All third-order retinal neurons tested were depolarized by kainic acid (KA, N-methyl-D-aspartate (NMDA), and quisqualate (QQ). The responses evoked by NMDA were blocked by the addition of D-2-amino-5-phosphonovaleric acid (D-AP5) and D-2-amino-7 phosphonoheptonoic acid (D-AP7) to the perfusate. When the actions of exogenously applied NMDA were completely blocked by D-AP5 and D-AP7, the light-evoked responses of inner retinal neurons persisted without any apparent reduction or, alternatively, a slight enhancement of the response was observed. Light-evoked responses of bipolar, amacrine, and ganglion cells associated with the On pathway were attenuated by L-AP5 in a manner similar to its lower-order homolog L-2-amino-4-phosphonobutyrate (AP4); nevertheless, L-AP5 was not an effective NMDA antagonist. Although synaptic transmission between retinal second- and third-order neurons appears to be mediated by EAARs, the NMDA receptor does not appear to play a prominent role under our experimental conditions. Nevertheless, our results suggest that the racemic mixture of AP5 should not be used as an NMDA antagonist in retinal research, due to the AP4-like actions of its L-enantiomer.

2-Amino-5-phosphonovalerate↗
PubMed1985

Characterization of an extended glutamate receptor of the on bipolar neuron in the vertebrate retina.

The synaptic receptors of ON bipolar neurons are selectively activated by 2-amino-4-phosphonobutyrate, a glutamate analogue. This agent uniquely distinguishes these receptors from other types of excitatory amino acid receptors found in the retina. Various glutamate and aspartate analogues were used to assess the structure-activity characteristics of this receptor. The results suggest that it represents one class of glutamate receptor which can be distinguished by its preferential activation by acidic amino acid analogues that match the extended conformation of glutamate.

Aminobutyrates↗
PubMed1985

Polarity of marginal-band microtubules in vertebrate erythrocytes.

Erythrocytes from three different vertebrate species (bullfrog, mudpuppy, and stinkpot) were isolated, and the polarity of the marginal-band microtubules was determined using a modification of the method described by Heidemann and McIntosh [12]. A considerable part of each marginal band was examined in serial sections to see whether any changes in the polarity pattern occurred along the length of the band. On the basis of analyses of over 45 marginal bands, the following observations were made: (i) different polarity patterns were present within a given species; (ii) the polarity pattern seen in one cross-section of the marginal band remained the same along its entire length; no evidence for a limited zone of overlap was obtained; (iii) centrioles were found in erythrocytes from all three species. The data on the polarity patterns and the presence of centrioles in erythrocytes are compatible with a model recently proposed for the organization of marginal-band microtubules in blood clams that invokes the activity of a microtubule organizing center [20]. We suggest that a modification of the process of marginal-band formation described in that model can account for our observations on the polarity of marginal-band microtubules.

Animals↗
PubMed1983

The role of excitatory amino acid transmitters in the mudpuppy retina: an analysis with kainic acid and N-methyl aspartate.

A variety of glutamate and aspartate analogues were used to characterize the excitatory amino acid receptors in the mudpuppy retina. This approach revealed two general classes of receptors which were represented by the agonists kainic acid and N-methyl aspartic acid. Kainic acid was found to be a potent photoreceptor transmitter agonist on all three types of second-order neurons, and it was a powerful excitant of amacrine and ganglion cells. N-Methyl aspartate had little effect in the outer retina, but it had potent stimulatory effects on inner retinal neurons. N-Methyl aspartate antagonists selectively blocked light responses in some sustained OFF ganglion cells. These results suggest that both photoreceptors and bipolar neurons may use glutamate Or an analogue, whereas aspartate may be utilized by a class of sustained ON amacrine cells.

Animals↗