Effects of noradrenaline on45Ca2+ efflux from isolated rat islets of Langerhans

Noradrenaline caused a prompt but transient increase in the rate of⁴⁵Ca²⁺ efflux from isolated rat islets of Langerhans perifused in Ca²⁺ depleted medium. The response was modest in size and was unaffected by isosmotic replacement of NaCl with choline chloride or by inclusion of 0.5 mM dibutyryl cAMP in the perifusion medium, suggesting that it was not mediated by Na+: Ca²⁺ exchange nor by lowered cAMP. Despite its effect on⁴⁵Ca²⁺ efflux, noradrenaline treatment did not alter the kinetics of⁴⁵Ca²⁺ efflux in response to the muscarinic agonist, carbamylcholine, nor did it change the magnitude of the response to this agent. Simultaneous introduction of 20 mM glucose with noradrenaline prevented a rise in⁴⁵Ca²⁺ efflux and indeed resulted in inhibition of⁴⁵Ca²⁺ efflux. The data suggest that noradrenaline does not directly activate the mechanisms which regulate Ca²⁺ extrusion from islets cells, and they do not support a primary role for the Ca²⁺ efflux response in mediating adrenergic inhibition of insulin secretion.     

A soluble chloroplast protein catalyzes ribulosebisphosphate carboxylase/oxygenase activation in vivo

Ribulosebisphosphate carboxylase/oxygenase (EC 4.1.1.39) (rubisco) must be fully activated in order to catalyze the maximum rates of photosynthesis observed in plants. Activation of the isolated enzyme occurs spontaneously, but conditions required to observe full activation are inconsistent with those known to occur in illuminated chloroplasts. Genetic studies with a nutant of Arabidopsis thaliana incapable of activating rubisco linked two chloroplast polypeptides to the activation process in vivo. Using a reconstituted light activation system, it was possible to demonstrate the participation of a chloroplast protein in rubisco activation. These results indicate that a specific chloroplast enzyme, rubisco activase, catalyzes the activation of rubisco in vivo.     

Intraspinal Tumors in Children

Thirty cases of intraspinal neoplasms occurring during the first two decades of life are reviewed. Histologic examination showed 13 of these to be astrocytomas, 6 neuroblastomas, 5 sarcomas, 3 ependymomas, 2 neurofibromas and 1 a schwannoma. Orthopedic deformities developed or worsened in 60 percent of patients surviving longer than a year after diagnosis. In five patients some form of endocrine deficiency developed after irradiation. For treatment of radiosensitive extradural malignant lesions, biopsy followed by irradiation is advocated.     

Taurodontism: A biometric study

This study has been carried out in order to clarify various aspects of the phenomenon known as taurodontism. Samples of both taurodont and non-taurodont teeth were measured and statistical analyses were performed on the resultant data from which various conclusions may be drawn. The most important conclusion is that this phenomenon may be defined metrically. The distributions have shown that the taurodont trait grades into the normal and it is quite difficult to make a subjective judgment at the low end of the taurodont range. It is for this reason that an accurate mathematical means for performing this task is so invaluable. The question of the nature of cuneiform single rooted molars was also investigated, and they were found not to be true taurodonts although the statistical procedure classed them as such. It was demonstrated that through the construction of simple plots these teeth could be eliminated from any group classed by analysis as taurodonts. Various metrical attributes were evaluated with respect to their ability to distinguish taurodonts, and two were found to be satisfactory for this purpose in most cases. Certain changes in molar morphology regarding caries and age were also investigated.     

Hormone-dependent processing of the avian progesterone receptor

Avian progesterone receptor exists as two forms, A and B, with molecular weights of 79,000 and 110,000 daltons, respectively. The origin and significance of these two forms is an area of active investigation and debate. Monoclonal antibodies produced against these two forms were used to examine receptor stability in cytosol and changes in the receptor forms induced by hormone binding. The lability of hormone binding at elevated temperatures is well documented. Analysis by Western blotting showed the receptor was stable in freshly prepared oviduct cytosol for 2 hr at 37°C, while hormone binding was lost within 30 min. However, loss of receptor through degradation was seen when cytosol was prepared from frozen tissue or when homogenization was excessive. Progesterone was injected into diethylstilbestrol-stimulated chicks to examine, in vivo, effects of hormone treatment on receptor forms in the cytosol and nuclear fractions. Progesterone treatment caused a time- and dose-dependent conversion of the A receptor to a form (A′) with a slower electrophoretic mobility. The cytosolic progesterone receptor was divided equally between the B and A forms, while the nuclear receptor was predominantly A′. The amount of nuclear receptor was consistently less than cytosolic receptor. Receptor phosphorylation was analyzed by incubating tissue minces with [³²P]orthophosphate with or without progesterone followed by immune isolation of receptor forms. Progesterone treatment caused a time-dependent increase in cytosol receptor phosphorylation which was evident after 5 min of treatment. This phosphorylation was observed with both the A and B receptor forms. The results indicate that receptor phosphorylation is a very early event during progesterone action.