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C Frelin

Publications and source records attributed to C Frelin.

At least 145 records · Page 8Linked to original sources
PubMed1982

The Ca2+-dependent slow K+ conductance in cultured rat muscle cells: characterization with apamin.

The interaction of apamin, a bee venom neurotoxin, with rat skeletal muscle cell membranes has been followed using both an electrophysiological and a biochemical approach. Voltage-clamp analyses have shown that apamin, at low concentrations, specifically blocks the Ca2+-dependent slow K+ conductance in rat myotubes and myosacs . A specific binding site for apamin in rat muscle cell membranes has been characterized with the use of a highly radiolabelled apamin derivative [( 125I]apamin). The dissociation constant for the apamin-receptor complex is 36-60 pM and the maximal binding capacity is 3.5 fmol/mg of protein. [125I]Apamin binding to rat muscle membranes is displaced by quinine and quinidine with K0.5 values of 110 microM and 200 microM, respectively.

Action Potentials↗
PubMed1982

Na+ channels with binding sites of high and low affinity for tetrodotoxin in different excitable and non-excitable cells.

The properties of interaction of tetrodotoxin with its receptor site on the voltage-sensitive Na+ channel were analysed in two ways: (a) by titrating Na+ channels with a tetrodotoxin derivative, [3H]ethylenediamine-tetrodotoxin; (b) by studying the physiological properties of interaction of the toxin with its receptor from 22Na flux measurements. Using a variety of cell types in culture, three different kinds of situations were observed. 1. Cells like N1E 115 neuroblastoma, CCl 39 fibroblasts, embryonic chick cardiomyocytes and chick skeletal myotubes only have one family of Na+ channels with high-affinity binding sites (in the nanomolar range) for tetrodotoxin. These Na+ channels are the same ones as those that are activated by the alkaloid and polypeptide toxins that accelerate 22Na+ influx. 2. C9 cells have Na+ channels with low-affinity binding sites for tetrodotoxin. These Na+ channels are also the ones that are activated by alkaloid and polypeptide toxins (the median inhibitory concentration for tetrodotoxin inhibition of 22Na+ influx through these Na+ channels in 300 nM). 3. Rat myotubes that have differentiated in culture in the absence of neuronal influence have both high-affinity binding sites (in the nanomolar range) detected with the tritiated tetrodotoxin derivative and low-affinity binding sites (on the micromolar range) detected by 22Na+ flux experiments. Only low-affinity binding sites correspond to Na+ channels that can be activated with alkaloid and polypeptide toxins.

Animals↗
PubMed1981

Purification and pharmacological properties of eight sea anemone toxins from Anemonia sulcata, Anthopleura xanthogrammica, Stoichactis giganteus, and Actinodendron plumosum.

Eight different polypeptide toxins from sea anemones of four different origins (Anemonia sulcata, Anthopleura xanthogrammica, Stoichactis giganteus, and Actinodendron plumosum) have been studied. Three of these toxins are new; the purification procedure for the five other ones has been improved. Sea anemone toxins were assayed (i) for their toxicity to crabs and mice, (ii) for their affinity for the specific sea anemone toxin receptor situated on the Na+ channels of rat brain synaptosomes, and (iii) for their capacity to increase, in synergy with veratridine, the rate of 22Na+ entry into neuroblastoma cells via the Na+ channel. Some of the toxins are more active on crustaceans, whereas others are more toxic to mammals. A very good correlation exists between the toxic activity to mice, the affinity of the toxin for the Na+ channel in rat brain synaptosomes, and the stimulating effect on 22 Na+ uptake by neuroblastoma cells. The observation has also been made that the most cationic toxins are also the most active on mammals and the least active on crustaceans. Toxicities (LD50) to mice of the most active sea anemone toxins and of the most active scorpion toxins are similar, and sea anemone toxins at high enough concentrations prevent binding of scorpion toxins to their receptor. However, scorpion toxins have affinities for the Na+ channel which are approximately 60 times higher than those found for the most active sea anemone toxins. Three sea anemone toxins appear to be more interesting than toxin II from A. sulcata (the "classical" sea anemone toxin) for studies of the Na+ channel structure and mechanism when the source of the channel is of a mammalian origin. Two of these three toxins can be radiolabeled with iodine while retaining their toxic activity; they appear to be useful tools for future biochemical studies of the Na+ channel.

Animals↗
PubMed1980

The regulation of protein turnover in newborn rat heart cell cultures.

The regulation of myocardial protein turnover was studied using newborn rat heart cells in monolayer cultures. Protein accumulation in this model system was regulated by the presence of serum in the culture medium. The influences of serum on the rates of protein synthesis and degradation were investigated. Serum deprivation or arginine deprivation did not modify protein synthesis. In contrast serum strongly inhibited the rates of [3H]leucine release from prelabeled long-lived myocardial proteins. The inhibiting serum factor was found heat-stable, displayed slight species specificity, was of plasmatic origin, and its activity was decreased in the plasma of hypophysectomized rats. Platelet growth factor, which promotes DNA synthesis in heart cell cultures, did not inhibit protein degradation. The influence of known regulators of myocardial protein balance was investigated. Leucine had no influence on protein synthesis and degradation. Supraphysiological concentrations of insulin and growth hormone inhibited protein degradation but only in the absence of serum. It is suggested that these compounds may not be the natural regulators of myocardial protein balance.

Animals↗
PubMed1980

Uridine phosphorylase activity during postnatal development of the rat heart.

Uridine phosphorylase activity was assayed in heart extracts from rats of different postnatal age. Activity was low at birth, increased to a maximum at 8--14 days of postnatal development and then decreased to a low adult level. The switch from cellular hyperplasia to hypertrophy determined by the ratio proteins/DNA occurred at day 18 of development. It is suggested that the activation of uridine phosphorylase activity during the early life of the rat may be a critical element of the onset of hypertrophy.

Animals↗
PubMed1980

Progesterone metabolism in newborn rat heart cell cultures.

Progesterone metabolism was studied in newborn rat heart cell cultures. The following enzymatic activities have been identified: 20 alpha-hydroxysteroid dehydrogenase, 3 alpha- and 5 alpha-hydroxysteroid oxidoreductases, and 6 alpha-hydroxylate. These activities are independent of sex and are probably related to the neonatal origin of the cells.

20-Hydroxysteroid Dehydrogenases↗
PubMed1980

Regulation of growth of newborn rat heart cell cultures: influence of cell density, pH, and a platelet-derived factor.

The search for elements regulating cardiac cell growth was undertaken using heart cell cultures as a model system. This model, derived from newborn rats, allowed the approach of the regulation of growth both at the cellular level and at a stage of incomplete differentiation of the muscle cells. The major control elements that have been identified are: 1) availability of essential nutrients; 2) proper regulation of the pH in the surrounding medium; 3) presence of serum survival factors and serum growth factors; and 4) homotypic and heterotypic cellular interactions. Specific examples pertaining to these different control elements are presented.

Animals↗