Efficient degradationin vitro of all intermediate filament subunit proteins by the Ca2+-activated neutral thiol proteinase from Ehrlich ascites tumor cells and porcine kidney

Vimentin, desmin, glial fibrillary acidic protein, neurofilament triplet proteins, and a mixture of cytokeratins were digested with Ca²⁺-activated neutral thiol proteinase isolated from Ehrlich ascites tumor (EAT) cells and porcine kidney. All intermediate filament proteins were degraded by the proteinase, although with different rates and Ca²⁺ optima. These results are in part at variance with our previous statement that the Ca²⁺-activated proteinase from EAT cells is specific for vimentin and desmin.     

Model of synchronized population bursts in electrically coupled interneurons containing active dendritic conductances

We constructed a computer model of 128 interneurons, each with multiple dendritic branches and an axonal segment. The model neurons were interconnected by gap junctions between dendritic compartments, as are known to occur in rat and guinea-pig hilar interneurons. The model contained no excitatory synapses. In the presence of low-frequency spontaneous action potentials, the model generated synchronized population bursts, when gap junction resistance was 50 M and there were at least two gap junctions per neuron on average. Population bursts occurred only when the dendrites of model neurons were electrically excitable. Consistent with experiment, somatic hyperpolarization during the population burst uncovered partial spikes. In the model, partial spikes originated in electrically active dendrites driven by coupled dendrites. This model may account for population bursts in hilar interneurons that occur in 4-aminopyridine (4AP) together with blockers of GABA_A and excitatory amino acid (EAA) receptors.     

A model of a human neuromuscular system for small isometric tensions

A model is constructed of the motor units in the human first dorsal interosseus (FDI) muscle. Each motorneuron is simulated using a pseudo-steady-state model that omits the membrane capacity and the events underlying the action potential. Properties of individual twitches in the corresponding muscle units are based on the data of Milner-Brown et al. for the FDI, while the transduction between steady firing rate and percentage of maximum tension in a muscle unit is based on the work of Rack and Westbury on the cat soleus muscle. Since we are concerned only with small isometric tensions, we ignore effects due to muscle spindles and to recurrent inhibition. The model allows one to to determine, by simulation, the tension-time functions produced by different programs of input to an entire pool of 120 motorneurons. Thus, for example, in order to produce tension rising linearly with time, it suffices to deliver to each neuron in the pool a non-linearly rising conductance; the conductance can be the same for all neurons in the pool, but can NOT be scaled in proportion to the surface area of the respective neurons. The input may be delivered to any part of the neuron's dendritic tree, as long as the electrotonic distribution of input is the same for all the neurons. For a linearly rising force produced in this way, most of the motorneurons yield similar slopes for their frequency-force curves, as observed by Milner-Brown et al. To produce tensions greater than about 1 kg, mechanisms not included in this model must come into play, i.e. perhaps introduction of phasic motorneurons. The most important data needed to improve this model are sets of isometric frequency-force curves for muscle units of different twitch tensions.     

Serum Calcium Response Following Oral Zinc Oxide Administrations in Dairy Cows

Six non-pregnant cows were allocated into 3 groups. Group 1 comprised a pair of lactating cows, whereas groups 2 and 3 each comprised a pair of non-lactating cows. The cows in groups 1 and 2 were dosed intraruminally by stomach tube with zinc oxide at 120 mg Zn per kg of bodyweight at weekly intervals for a period of 33 days. Each cow received a total of 4 doses of zinc oxide. Group 3 served as non-treated control group. Blood samples were collected from all 6 cows daily. Serum was analysed for concentration of calcium. Within 12–24 h of each zinc oxide administration the serum calcium of the lactating cows dropped dramatically indicating the existence of an antagonistic effect between Zn and Ca. The first Zn induced hypocalcaemic episode in the lactating cows was followed by a rise in serum calcium to a level above the pre-dosing level and above the mean value of the control group. The depth of the hypocalcaemic response decreased with the number of zinc oxide dosings. This effect was explained as a response from the stimulation of the calcium homeostatic mechanisms. In the Zn dosed non-lactating cows responses were similar but less clear. The perspective of these findings is discussed in relation to resistance towards parturient hypocalcaemia.     

Membrane phenotype and response to deoxycoformycin in mature T cell malignancies.

The adenosine deaminase inhibitor deoxycoformycin was used in low doses to treat 19 patients with clinically aggressive T cell malignancy with a mature membrane phenotype. The patients comprised eight with prolymphocytic leukaemia, two with chronic lymphocytic leukaemia, four with adult T cell leukaemia-lymphoma, three with Sézary syndrome, and two with T cell lymphoma. Two thirds of the patients had been resistant or minimally responsive to combination chemotherapy. Complete remission was obtained in five patients (two with prolymphocytic leukaemia and one each with chronic lymphocytic leukaemia, adult T cell leukaemia-lymphoma, and Sézary syndrome) and partial remission in two others. Unmaintained complete remission lasting more than one year was seen in three patients. Responses were obtained only in patients with CD4+,CD8-membrane markers (seven out of 10), and no responses were recorded in any of the nine patients with a different phenotype. In this series remission appeared to correlate with the membrane phenotype of the neoplastic cell and not with the cytopathological diagnosis. Future studies should establish the biochemical basis for the greater sensitivity of CD4+ lymphoid cells to deoxycoformycin.     

The diabetic rat kidney mediates inosituria and selective urinary partitioning of D-chiro-inositol

Diabetic nephropathy is a serious complication of diabetes mellitus with a pressing need for effective metabolic markers to detect renal impairment. Of potential significance are the inositol compounds, myo-inositol (MI), and the less abundant stereoisomer, D-chiro-inositol (DCI), which are excreted at increased levels in the urine in diabetes mellitus, a phenomenon known as inosituria. There is also a selective urinary excretion of DCI compared to MI. As the biological origins of altered inositol metabolism in diabetes mellitus are unknown, the aim of this study was to determine whether the diabetic kidney was directly responsible. Kidneys isolated from four-week streptozotocin-induced diabetic rats were characterized by a 3-fold reduction in glomerular filtration rate (GFR) compared to matched non-diabetic kidneys. When perfused with fixed quantities of MI (50 µM) and DCI (5 µM) under normoglycemic conditions (5 mM glucose), GFR-normalized urinary excretion of MI was increased by 1.7-fold in diabetic vs. non-diabetic kidneys. By comparison, GFR-normalized urinary excretion of DCI was increased by 4-fold. Perfusion conditions replicating hyperglycemia (20 mM glucose) potentiated DCI but not MI urinary excretion in both non-diabetic and diabetic kidneys. Overall, there was a 2.4-fold increase in DCI urinary excretion compared to MI in diabetic kidneys that was independent of glucose ambience. This increased urinary excretion of DCI and MI in diabetic kidneys occurred despite increased renal expression of the inositol transporters, sodium myo-inositol transporter subtype 1 and 2 (SMIT1 and SMIT2). These findings show that the diabetic kidney primarily mediates inosituria and altered urinary partitioning of MI and DCI. Urinary inositol levels might therefore serve as an indicator of impaired renal function in diabetes mellitus with wider implications for monitoring chronic kidney disease.     

Gap junctions in several tissues share antigenic determinants with liver gap junctions.

Using affinity-purified antibodies against mouse liver gap junction protein (26 K), discrete fluorescent spots were seen by indirect immunofluorescence labelling on apposed membranes of contiguous cells in several mouse and rat tissues: pancreas (exocrine part), kidney, small intestine (epithelium and circular smooth muscle), Fallopian tube, endometrium, and myometrium of delivering rats. No reaction was seen on sections of myocardium, ovaries and lens. Specific labelling of gap junction plaques was demonstrated by immunoelectron microscopy on ultrathin frozen sections through liver and the exocrine part of pancreas after treatment with gold protein A. Weak immunoreactivity was found on the endocrine part of the pancreas (i.e., Langerhans islets) after glibenclamide treatment of mice and rats, which causes an increase of insulin secretion and of the size as well as the number of gap junction plaques in cells of Langerhans islets. Furthermore, the affinity purified anti-liver 26 K antibodies were shown by immunoblot to react with proteins of similar mol. wt. in pancreas and kidney membranes. Taken together these results suggest that gap junctions from several, morphogenetically different tissues have specific antigenic sites in common. The different extent of specific immunoreactivity of anti-liver 26 K antibodies with different tissues is likely due to differences in size and number of gap junctions although structural differences cannot be excluded.     

Clathrin-associated adaptor proteins - putting it all together

Adaptors are multifunctional linker proteins that, as a coated vesicle assembles, tether the clathrin lattice to the underlying membrane bud site. Each adaptor is composed of four distinct protein submits, but how these assemble into the functional complex is not clear. Here, some features of the protein sequences are discussed in an attempt to develop a speculative, low-resolution structural model of possible subunit interactions.