Identified taste bud cell proliferation in the perihatching chick [published erratum appears in Chem Senses 1998 Aug;23(4):459]

Developing taste buds in the anterior mandibular floor of perihatching chicks were studied by high voltage electron microscopic autoradiography in order to identify proliferating gemmal cell types. Montaged profiles of 29 taste buds in five cases euthanized between embryonic day 21 and posthatching day 2 were analyzed after a single [3H]thymidine injection administered on embryonic day 16, 17 or 18. Results showed that dark cells comprised 55% of identified (n = 900 cells) and 62% of labeled (n = 568 cells) gemmal cells as compared with light, intermediate, basal or perigemmal bud cells. Dark cells had both a greater (P < 0.05) number of labeled cells and a greater amount of label (grains/nucleus) than the other four bud cell types, irrespective of injection day. The nuclear area (micron 2) of dark cells was not significantly larger (P > 0.05) than that of the other gemmal cell types and therefore cannot account for the greater amount for label in the dark cells. Interestingly, only dark cells showed a positive correlation (P < 0.003) between amount of label and nuclear area. Results suggest that, during the perihatching period of robust cell proliferation, dividing dark cells may give rise primarily, but not exclusively, to dark cell progeny.      

TTX-induced muscle disuse alters Ca2+ activation characteristics of myofibril ATPase.

1. Previous reports of the effects of disuse induced by tetrodotoxin (TTX) have demonstrated alterations in muscle function suggesting changes in the quality of contractile proteins. 2. We extended these studies to the effects of TTX-induced disuse on the Ca2+ activation characteristics of myofibrillar ATPase of the rat gastrocnemius. 3. Atrophic responses were as previously reported (St-Pierre, D.M.M. and Gardiner P.F. (1985) Effect of disuse on mammalian fast-twitch muscle: joint fixation compared with neurally applied tetrodotoxin. Exp. Neurol. 90, 635-651; St-Pierre, D.M.M. et al. (1987). Recovery of muscle from tetrodotoxin-induced disuse and the influence of daily exercise; 1. Contractile properties. Exp. Neurol. 98, 472-488.) with a significant decrease in left gastrocnemius weight compared to control (C) (1.25 +/- 0.06 for C vs 0.72 +/- 0.04 for TTX, X +/- SEM, P less than or equal to 0.01). 4. Myofibrillar protein yield (mg/g wet weight) was also depressed (92.8 +/- 4.5 for C vs 70.3 +/- 3.7 for TTX; P less than or equal to 0.01). 5. Maximum ATPase of myofibrils (nmol Pi/mg/min) was decreased (441 +/- 28 for C vs 181 +/- 30 for TTX, P less than or equal to 0.01). 6. Furthermore, the Hill n which reflects the cooperative aspects of Ca2+ activation of the myofibrillar ATPase was depressed (1.58 +/- 0.07 for C vs 1.29 +/- 0.09 for TTX; P less than or equal to 0.01). 7. The results suggest that muscle perturbations resulting from disuse are partially related to changes in the myofibril.     

Multiple binding components for methyltrienolone in canine prostatic epithelial cells

Using a whole cell assay system, the androgen binding capacity of canine prostatic epithelial cells was evaluated in relation to their function. Radiolabeled Methyltrienolone (R1881) was used as the ligand in the presence of an excess of Triamcinolone acetonide and the amount of [3H]R1881 bound to the cells at equilibrium was determined by either displacement or saturation studies. With immature cells in culture (3 days of attachment), displacement analysis revealed the presence of high affinity binding sites which were also present in cells cultured for 10 days. With freshly dispersed prostatic cells (mostly secretory epithelial cells) as well as with older cells in culture (17 and 24 days), only less specific binding sites were observed with both unlabeled R1881 and/or dihydrotesterone (DHT). In contrast, only the high affinity androgen receptor (AR) was present in cytosolic extracts prepared from normal glands. Displacement studies performed with cultured cells at different stages of growth also showed that the basal level as well as the degree of low affinity binding increased during the maturation of non-proliferating cells. The presence of multiple binding components was demonstrated by saturation studies performed with either cultured or freshly dispersed cells. The first component, that was saturated at 5 nM of [3H]R1881, was due to AR while the other two binding components, showing positive-cooperativity (Hill coefficients of 1.90 and 5.07, respectively), were saturated at concentrations of 15 and 30 nM of [3H]R1881. In contrast, the Hill coefficient for the AR was 0.88 indicating the presence of an independent component. It was calculated that only 11.4% of the total uptake of R1881 was attributed to AR binding, suggesting that the remainder may represent an intracellular pool of androgens. Thus, a whole cell binding assay represents a dynamic system for the detection, by saturation studies, of binding components that are not revealed using the conventional displacement studies or cell-free systems. It is proposed that these acceptor sites may play a role in differentiated prostatic function rather than in cell proliferation.