1,721,056 research outputs found
Phosphorylation of specific polypeptides induced by 12-O-tetradecanoylphorbol-13-acetate in chick embryo fibroblasts.
No full textThe tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induces, in cultured chick embryo fibroblasts, a generalised increase of the incorporation of labelled inorganic phosphate, and stimulates the phosphorylation of at least two polypeptide bands, 26 K and 65 K. Stimulation of the phosphorylation of 26 K and 65 K occurs within minutes of the addition of TPA to the culture medium of chick embryo fibroblasts, but it can also be evidenced at later times. Removal of TPA from the culture medium causes reversion of this effect. Stimulation of the phosphorylation of 26 K is also induced by the Ca2+-ionophore A23187, but the calmodulin inhibitor trifluoperazine does not inhibit the TPA induced stimulation of polypeptide phosphorylation. Agents increasing the intracellular cAMP concentration do not stimulate the phosphorylation of 26 K and 65 K. The results obtained suggest that the phosphorylation of specific polypeptides, probably induced by TPA through a Ca2+-phospholipid dependent mechanism, may represent an early regulative event which may be relevant for the pleiotropic effect of TPA in cultured normal cells
Cyclic AMP regulates the life time of acetylcholine-activated channels in cultured myotubes
No full text'Giga-seal' patch-clamp recording was performed in embryonic chick myotubes at day 3 to 4 of culture. Myotubes were exposed to agents that enhance the concentration of cytosolic cyclic AMP (cAMPi) and their action on acetylcholine- (ACh) activated channels was investigated. While the conductance and the closed time was unaffected by forsokolin, cholera toxin, dibutyryl cyclic AMP and 8-bromo-cyclic AMP, these agents lengthened the ACh-activated channel life time with efficacy that paralleled with their capability to increase the cAMPi
ARGININE-VASOPRESSIN INDUCES DIFFERENTIATION OF SKELETAL MYOGENIC CELLS AND UP-REGULATION OF MYOGENIN AND MYF-5
No full textThe neurohypophyseal nonapeptide arginine(8)-vasopressin (AVP) induces phosphoinositide turnover and calcium and pH changes in skeletal myogenic cells in culture. In order to investigate the effect of AVP on skeletal myogenesis, we examined the effect of this hormone on proliferating mononucleated L6 myoblast cultures. Addition of AVP to the medium resulted in the formation of much larger myotubes than those formed in its absence and in a significant increase (2.2-fold) of the percentage of fusion within 3-4 days of treatment. The effect of AVP was dose dependent, in the 10 nM to 1 mu M range, and was observed also in primary cultures of mouse satellite cells. The rate of growth of L6 cells was not affected by AVP treatment. The induction of morphological differentiation by AVP correlated with an increased expression of muscle-specific gene products, such as myosin, and an increased number of acetylcholine receptor sites. The accumulation of mRNA transcripts of the acetylcholine receptor subunits was also enhanced by AVP. The mechanism involved in the myogenic action of AVP was investigated. Using AVP-related peptides and antagonists, we found that a specific chemical structure is required and that V1 receptors probably mediate the effect on myogenesis. Expression of muscle-specific transcription factor genes Myf-5 and myogenin and their products are strongly upregulated by AVP. Our findings support the hypothesis that AVP may represent a novel physiological modulator of skeletal muscle differentiation through its action on muscle regulatory genes
Cell fusion and creatine kinase activity in cultures of chick embryo myoblasts
No full textIn primary cultures of myoblasts from embryonic chick skeletal muscle, cells undergo a period of proliferation lasting 2 days, and then fuse into multinucleated myotubes. It is a generally accepted idea that cell fusion represents a critical event followed by the synthesis of specific proteins. It was reported that no specific enzymes are synthesized by mononucleated myoblasts (COLEMANan d CoLEhiAN, 1968; SHAINBEReGt ul., 1971; LOOMIS el al., 1973). We investigated the relationship between cell fusion and the activity of specific enzymes, in order to verify whether the expression of these phenomena is linked to a common regulative signal. The activity of creatine kinase (CPK; E.C. 2. 7. 3 2.) has been investigated in culture conditions which prevent cell fusion without affecting cell growth. These culture conditions consisted of the use of a nutritional medium at low serum concentration (MOLINAROet al., 1974). The inhibition of cell fusion obtained by low serum concentration depends primarily on the reduced Ca++ concentration, since the addition of Ca++ restores cell fusion
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