Effects of feeding a single or sequence of beta-adrenergic agonists on cull cow meat quality.

Sixty cull cows were implanted and assigned to four treatments: C = concentrate ration only; RH = supplemented with ractopmaine-HCl (8.33 mg/kg of feed) for 25 d; ZH = supplemented with zilpaterol-HCl (ZH) (200mg head (-1)d(-1)) for the last 20 d; and RH + ZH = supplemented with RH for 25 d followed by ZH for 20 d. All cows were fed a concentrate ration for 74 d. Infraspinatus steaks from cows supplemented with RH and/or ZH had lower (P<0.05) shear force than steaks from C cows. Longissimus (LM) steaks from the 6-8th rib section of ZH and RH+ZH cows had decreased (P<0.0001) desmin degradation at 10 and 21 d postmortem compared to steaks from C and RH cows. Collagen solubility of the LM was increased (P<0.05) by ZH and RH+ZH compared to C. There were no treatment differences in 12th rib LM tenderness when enhanced with calcium lactate. Color and sensory traits of meat from RH+ZH cows were not different from C but flavor intensity was greater and off-flavor less than for C cows.

Complete sequence of a cDNA encoding an active rat choline acetyltransferase: a tool to investigate the plasticity of cholinergic phenotype expression.

A cDNA clone encoding the complete sequence of an active rat choline acetyltransferase (ChoAcTase; acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6) has been isolated. Analysis of the deduced amino acid sequence reveals 85% and 31% identity with the porcine and Drosophila melanogaster enzymes, respectively. To further elucidate the molecular basis of neurotransmitter-related phenotypic plasticity, the expression of ChoAcTase mRNA was compared with that of tyrosine hydroxylase [TH; tyrosine 3-monooxygenase, L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2], in neurons from superior cervical ganglia grown in the following conditions: 1) normal medium, 2) high K+ medium, and 3) normal medium supplemented with 50% muscle-conditioned medium (CM). TH mRNA was expressed in all three media; its level rose in high K+ and decreased strikingly in the presence of CM. ChoAcTase mRNA could be visualized in CM, but fell to undetectable levels in normal and high K+ media. These results suggest that translational or post-translational mechanisms do not play a major role for the modulation of neurotransmitter-associated phenotype.

The use of a tyrosine-hydroxylase cDNA probe to study the neurotransmitter plasticity of rat sympathetic neurons in culture.

We have compared quantitatively the effects of muscle-conditioned medium (CM) and elevated K+ concentration (40 mM) on the enzymatic activity of tyrosine hydroxylase (TH) and on TH-mRNA levels in primary cultures of rat sympathetic neurons. Northern blot analysis of RNA from cultured neurons with a 32P-labeled rat TH-cDNA probe was performed. The probe hybridized strongly with a single RNA species of 1.9 kb, similar in size to the TH-mRNA from PC12 pheochromocytoma cells. In agreement with earlier data both CM and a partially purified factor from CM increased choline acetyltransferase activity up to 200-fold and depressed TH activity by 2- to 7-fold in cultured sympathetic neurons. These effects were accompanied by a decrease in TH-mRNA level, which correlated with the decrease in TH activity. On the other hand, a culture medium supplemented with 40 mM KCl caused a 1.5- to 5-fold increase in TH activity, which was accompanied by an increase in TH-mRNA level of the same order of magnitude. As a working hypothesis, we suggest that CM and neuronal depolarization control the transcription of the TH gene in an antagonistic manner.

Effect of membrane phospholipid composition changes on adenylate cyclase activity in normal and rous-sarcoma-transformed chicken embryo fibroblasts.

Adenylate cyclase specific activities in membranes isolated from chicken embryo fibroblasts transformed by Rous sarcoma virus are significantly lower than the specific activity of the enzyme in normal membranes. Since normal and transformed membranes have different phospholipid and fatty acid compositions, adenylate cyclase activities were examined in normal and transformed membranes which had been supplemented with polar head groups or fatty acids. Basal, fluoride, and prostaglandin E1-stimulated activities changed systematically with phospholipid composition. Increases in the primary amino group of the phospholipid polar head groups or the average degree of fatty acid unsaturation both inhibited adenylate cyclase activity. In general, adenylate cyclase activities in normal membranes were more sensitive to phospholipid compositional changes compared to adenylate cyclase in transformed membranes. The data indicate that the lower adenylate cyclase activities in transformed membranes are not solely attributable to phospholipid changes but do suggest that increases in the percentage of phosphatidylethanolamine may contribute to the lower adenylate cyclase activities in transformed membranes.

Potassium fluxes and ouabain binding in growing, density-inhibited and Rous sarcoma virus-transformed chicken embryo cells.

Potassium fluxes, ouabain binding, and Na+ and K+ intracellular concentrations were determined for cultures of growing normal, density-inhibited and Rous sarcoma virus-transformed chicken embryo fibroblasts. No significant differences in K+ influx or ouabain binding were detected between growing normal cells and Rous sarcoma virus-transformed cells; however, ouabain binding and ouabain-sensitive K+ influx were 1.5- to 1.8-fold lower in density-inhibited cells. Thus, potassium influx in this system can be classified as a growth-related, but not transformation-specific change. As determined by both flame photometry and radioisotopic (42K) equilibration, growing normal and density-inhibited cells had similar potassium contents, whereas transformed cells exhibited 1.4-fold higher potassium levels. Sodium ion levels, as measured by flame photometry, were also 2- to 4.5-fold higher in transformed than normal or density-inhibited cells. Complementary studies of potassium efflux showed a 1.3- to 1.5-fold higher rate (based on the percentage of pool exiting the cell) in growing normal versus density-inhibited or transformed fibroblasts. Because of the larger potassium pool in transformed cells, efflux based on absolute number of potassium ions is similar in normal and transformed chicken embryo fibroblasts.