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C Collin

Publications and source records attributed to C Collin.

10 recordsLinked to original sources
PubMed1992

Long-term transformation of an inhibitory into an excitatory GABAergic synaptic response.

For a constant membrane potential, a predominantly inhibitory GABAergic synaptic response is shown to undergo long-term transformation into an excitatory response after pairing of exogenous gamma-aminobutyric acid (GABA) with postsynaptic depolarization or pairing of pre- and postsynaptic stimulation. Current- and voltage-clamp experiments suggest that this synaptic transformation is due to a shift from a net increase of conductance to a net decrease of conductance in response to GABA. GABA-induced elevation of intracellular calcium is prolonged after the same stimulus pairing and may, therefore, contribute to this synaptic transformation via Ca(2+)-activated phosphorylation pathways. This synaptic transformation, which does not follow unpaired stimulus presentations, occurs in a neuronal compartment spatially separated from the soma, which also changes during stimulus pairing.

Animals↗
PubMed1992

Characterization of human cytokeratin 2, an epidermal cytoskeletal protein synthesized late during differentiation.

Among the more than 30 different human proteins of the cytokeratin (CK) group of intermediate filament (IF) proteins, the significance of the epidermal polypeptide CK 2 (Moll et al., 1982, Cell 31, 11-24) has been repeatedly questioned in the literature. Here, we show, by in vitro translation and protein gel electrophoresis, that human epidermis from various body sites does indeed contain relatively large amounts of mRNA encoding a distinct polypeptide comigrating with native epidermal CK 2. We also report the isolation of a cDNA clone encoding the complete sequence of CK 2, which is a type II CK different from--but related to--epidermal CKs 1 and 5 on the one hand and corneal CK 3 on the other. The mRNA of approximately 2.6 kb encodes a polypeptide of 645 amino acids and M(r) 65,852, in good agreement with the value of 65.5 kDa previously estimated from gel electrophoresis. This human CK, the largest so far known, displays several features typical of CKs of stratified epithelia, including numerous repeats of glycine-rich tetrapeptides in the head and tail domains. Northern blot and in situ hybridizations have shown that CK 2 is expressed strictly suprabasally, usually starting in the third or fourth cell layer of epidermis, and this was confirmed at the protein level by immunohistochemistry using CK 2-specific antibodies. The protein has been detected as a regular epidermal component in skin samples from different body sites, albeit as a minor CK in "soft skin" (e.g., breast nipple, penile shaft, axilla), but not in foreskin epithelium and in other epithelia, in squamous metaplasias and carcinomas, or in cultured cell lines derived therefrom. We propose that CK 2 is a late cytoskeletal IF addition synthesized during maturation of epidermal keratinocytes which probably contributes to terminal cornification.

Amino Acid Sequence↗
PubMed1992

The role of calcium in prolonged modification of a GABAergic synapse.

Caudal hair cell impulses cause postsynaptic inhibition of ipsilateral type B photoreceptors in the snail Hermissenda. This inhibition is shown to be GABAergic according to a number of criteria. HPLC, mass spectrophotometric, and immunocytochemical techniques demonstrated the presence of GABA in the hair cells and their axons. GABA agonists and antagonists mimic and block the synaptic effect in a manner consistent with endogenous GABAergic transmission. Other properties, including I-V relations, conductance changes and reversal potentials, are comparable for exogenous GABA responses and endogenous effects of the hair cell impulses. This inhibitory synapse has been found to undergo a long-lasting transformation into an excitatory synapse if GABA release is paired with post-synaptic depolarization. GABA, via GABAA and GABAB receptors in the B cell, causes the opening of calcium sensitive chloride and potassium channels that leads to the post-synaptic hyperpolarization. GABA also induces a long-lasting intracellular calcium elevation at the terminal branches of the B cell that greatly outlasts the voltage responses. Synaptic transformation induced by pairings is caused by a decrease in both GABA induced chloride and potassium conductances in the post-synaptic B cell, as well as a significant prolongation of the intracellular calcium accumulation in the B cell's terminal axonal branches.

Animals↗
PubMed1992

Biophysical and behavioral correlates of memory storage, degradation, and reactivation.

Neural correlates of associative memory and "forgetting" were observed 1, 6, and 14 days after acquisition of a conditioned response (CR) in the marine snail Hermissenda. Behavioral expression of a light-rotation association, as indexed by contraction of the animal's foot in response to light, dissipated throughout the 14-day interval such that a CR was observed 1 and 6 days after conditioning but was absent 14 days later. In relation to naive or pseudoconditioned animals, membrane resistance (inversely related to neuronal membrane conductance and directly related to excitability) of the isolated Type B photoreceptor (B cell) was elevated in conditioned animals on Days 1 and 6, whereas no elevation was detectable on Day 14. However, both the behavioral response and the elevated membrane resistance in conditioned animals were hypersensitive to light-rotation pairings (i.e., exhibited "savings") on Day 14, which is indicative of a latent memory trace. In a second experiment, a current-induced depolarization of the B cell after 14 retention days resulted in an increase in input resistance of the B cell membrane in previously conditioned animals but a weaker, transient rise in resistance in B cells from animals exposed to the nonassociative control procedure 14 days earlier. This effect was Ca(2+)-dependent because no rise in resistance was observed if Ca2+ was removed from the extracellular bath. These results indicate that modification of membrane conductance (i.e., elevated resistance), although apparently critical for the behavioral expression of the memory, is not essential for the maintenance of the latent memory trace, whereas Ca2+ hypersensitivity may be a principal contributor to the storage of a latent memory trace and memory reactivation.

Animals↗
PubMed1992

Suprabasal marker proteins distinguishing keratinizing squamous epithelia: cytokeratin 2 polypeptides of oral masticatory epithelium and epidermis are different.

Terminal differentiation of squamous epithelia is usually characterized by the synthesis of a subset of cytokeratins (CKs) in suprabasal cell layers which become major components of the intermediate filament (IF) bundle cytoskeleton of the maturing cells. We have examined the significance, molecular nature and pattern of synthesis of the elusive human CK 2 by analyzing mRNAs from certain stratified epithelia, using in vitro translation, cDNA cloning. Northern blotting and in situ hybridization. We show that genuine polypeptides with the typical gel electrophoretic mobility of CK 2 exist but that the CK 2 present in the masticatory epithelia of hard palate and gingiva (CK 2p) differs from that found in epidermis (CK 2e) by its amino acid sequence and is encoded by a different gene. The two CKs 2 show only limited sequence homology (71% identical amino acid positions in the rod domain), and the oral CK 2p is more closely related to the corneal CK 3 (86%), as is also indicated by the cross-reaction of monoclonal antibody AE5. By in situ hybridization and immunocytochemistry, we further show that both CK 2e and CK 2p are expressed only in suprabasal cell layers of the specific epithelia where they can accumulate to represent major cytoskeletal proteins. We discuss this tissue-type specificity of CK 2 synthesis in otherwise morphologically and biochemically similar epithelia in relation to differences of IF appearance and packing in upper strata between epidermal and masticatory epithelia as well as to tissue formation and differentiation during development.

Amino Acid Sequence↗
PubMed1975

Infusion thrombophlebitis and infection with various cannulas.

A prospective study was carried out of the frequency of thrombophlebitis and bacterial contamination of cannulas associated with four commonly used intravenous cannulas of differing length and chemical composition. For all cannulas the frequency of thrombophlebitis increased significantly with time. Long 'Teflon' cannulas were significantly more likely to be contaminated with bacteria and associated with thrombophlebitis than all other cannulas, while the low frequency of thrombophlebitis with butterfly stainless steel cannulas was shown to be due to their short duration of use. It is suggested that long teflon cannulas should be avoided and that infusion thrombophlebitis could be eliminated as a clinical problem by the use of intermittent short duration intravenous infusions.

Bacteriological Techniques↗