Are ions involved in the gating of calcium channels?

The rates of activation and deactivation of the currents carried by calcium, strontium, or barium ions through the voltage-sensitive calcium channel of Paramecium are different. The differences cannot be attributed to complications due to internal ion concentration, calcium channel inactivation, potassium current activation, surface charge effects, or incomplete space clamping. The findings indicate participation of the divalent cations in the voltage-driven calcium channel gating process.

Abnormal rheology of oxygenated blood in sickle cell anemia.

The viscosity of oxygenated blood from patients with sickle cell anemia (Hb SS disease) was found to be abnormally increased, a property which contrasts with the well recognized viscous aberration produced by deoxygenation of Hb SS blood. Experiments designed to explain this finding led to considerations of deformation and aggregation, primary determinants of the rheologic behavior of erythrocytes as they traverse the microcirculation. Deformability of erythrocytes is in turn dependent upon internal viscosity (i.e. the state and concentration of hemoglobin in solution) and membrane flexibility. Definition of the contribution made by each of these properties to the abnormal viscosity of oxygenated Hb SS blood was made possible by analysis of viscosity measurements, made over a wide range of shear rates and cell concentrations, on Hb SS erythrocytes and normal erythrocytes suspended in Ringer's solution (where aggregation does not occur) and in plasma. Similar measurements were made on the two cell types separated by ultracentrifugation of Hb SS erythrocytes: high density erythrocytes composed of 50 to 70% irreversibly "sickled" cells (ISC) and low density erythrocytes composed of over 95% non-ISC. Under all experimental conditions (hematocrit, shear rate, and suspending medium) the viscosity of ISC exceeds that of normal erythrocytes. The viscosity of non-ISC is elevated only in the absence of aggregation and over intermediate ranges of hematocrit. Analyses of the data reveal (a) an elevated internal viscosity of ISC: (b) a reduced membrane flexibility of both ISC and non-ISC, particularly at low shear rates; and (c) a reduced tendency for aggregation displayed by both cell types. The abnormal viscosity of oxygenated Hb SS blood can be attributed to the altered rheology of ISC and, to a lesser extent, of non-ISC. These studies assign a role to the abnormal rheology of Hb SS erythrocytes in the pathogenesis of sickle cell anemia, even under conditions of complete oxygenation.

Abnormal membrane sodium transport in Liddle's syndrome.

We have documented the presence of abnormal sodium transport in Liddle's syndrome by measuring sodium concentration, sodium influx, and fractional sodium outflux in vitro in erythrocytes from normal subjects, two patients with Liddle's syndrome, and one patient with primary hyperaldosteronism. Sodium influx and fractional sodium outflux, but not sodium concentration, were significantly increased in patients with Liddle's syndrome. Sodium outflux in a patient with primary hyperaldosteronism did not differ significantly from normal. These alterations of sodium transport in erythrocytes from patients with Liddle's syndrome were not attributable to circulating levels of aldosterone, renin, angiotensin, or serum potassium. Furthermore, changes in aldosterone secretory rate and levels of circulating renin produced by varying dietary sodium intake, did not alter sodium influx or fractional sodium outflux in either patients with Liddle's syndrome or normal subjects. The response of fractional sodium outflux and sodium influx to ouabain, ethacrynic acid, and to changes in the cation composition of the incubation medium suggests that the increased sodium fluxes in Liddle's syndrome do not result solely from a quantitative increase in those components of sodium transport which occur in normal human erythrocytes. Instead, at least a portion of the increased erythrocyte sodium transport in Liddle's syndrome represents a component of sodium transport which does not occur in normal human erythrocytes.

Role of platelet membrane in enhancement of tumor cell adhesion to endothelial cell extracellular matrix.

Tumor cell adhesion to subendothelial matrix in the presence of platelets and plasma has been examined in vitro using an entirely homologous system of rat Walker 256 carcinosarcoma cells, matrix laid down by rat aortic endothelial cells and rat platelets and plasma. In the presence of platelets or platelets plus plasma, tumor cell adhesion was significantly enhanced when compared to adhesion in the absence of platelets. In the presence of plasma alone (0.1%), we observed no significant increase in tumor cell adhesion. In order to determine which platelet factors contribute to the enhancement of tumor cell adhesion by platelets, we subjected washed rat platelets to mechanical lysis or thrombin stimulation followed by centrifugation. The membrane fractions and supernatant fractions containing platelet attachment proteins were compared for their abilities to support tumor cell adhesion to subendothelial matrix. Platelet membranes were also recombined with platelet supernatant fractions to determine if platelet attachment proteins or platelet membranes required the presence of the other to enhance tumor cell adhesion. Platelet supernatant fractions which contained release reaction proteins (confirmed by polyacrylamide gel electrophoresis) did not enhance tumor cell adhesion. Purified thrombospondin, fibronectin, beta-thromboglobulin, platelet derived growth factor, and serotonin had no effect on tumor cell adhesion. Platelet membrane containing fractions affected tumor cell adhesion to subendothelial matrix as follows: (a) platelets formed an adhesive bridge between tumor cells and the subendothelial matrix as demonstrated by scanning electron microscopy; (b) intact platelets and thrombin stimulated platelets were the most effective at facilitating tumor cell adhesion; (c) preparations containing partially lysed platelet ghosts were more effective in supporting tumor cell adhesion to subendothelial matrix than were preparations containing completely lysed platelet membrane fragments; (d) recombination of platelet supernatant fractions with mechanically lysed platelets did not enhance their ability to support adhesion; (e) fixed platelets, either alone or in combination with platelet supernatant fractions, failed to enhance adhesion. These data indicate that platelet enhanced tumor cell adhesion appears to be dependent on platelet membrane factors including receptor mobility, rather than intraplatelet components.

The blood vessels of the skin.

During the last 25 years, cutaneous biologists have been particularly interested in abnormal cutaneous vascular patterns, the profusion of capillary anastomoses, the leakiness of venules, clotting, fibrinolysis, and blood viscosity. As a result, the effects of hypoxia and the factors that encourage new vessel proliferation are better understood than before. Only when the biologic behavior of the two extremes of growth from hypoplasia to hyperplasia is studied and compared can the blood supply of a tissue be understood. Hyperplastic tissues are seen in wounds, psoriasis, cancer, and in selected sites of chronic stasis and hypoxia where the vessels are extremely permeable, where blood cells easily escape, and where lymphatics dilate and proliferate. The proliferation of other tissues, such as endothelium, epithelium, mast cells, and probably of locally infective organisms, is also encouraged in hyperplasia. Moreover, fibrinolysis does not occur and fibrin is deposited, the electrostatic charge on the internal vascular surface becomes more positive, and the organ is more vulnerable to subsequent injury. Atrophic or hypoplastic tissues have a reduced cellular turnover and are less hypoxic. The vessels are less permeable, blood cells do not escape, there is only a slight tendency to clot, and fibrinolysis is often increased. Lymphatics are sparse and infection is not a feature. The electrostatic charge on the internal surface of the vessel is negative.

Duchenne dystrophy: electron microscopic findings pointing to a basic or early abnormality in the plasma membrane of the muscle fiber.

In seven patients with Duchenne dystrophy, high-resolution phase microscopy demonstrated a population on non-necrotic fibers with one or more focal lesions. The typical lesion was wedge-shaped, with the base resting on the fiber surface. In the electron microscope, the plasma membrane overlying the lesion was either absent or disrupted, while the basement membrane was always preserved. Within the lesion, there were cytoplasmic abnormalities, and in the neighboring fiber region, the myofibrils were usually highly contracted. The structural defect in the plasma membrane suggested that this site was an ineffective cellular barrier. This was confirmed by the frequent ingress of peroxidase-containing extracellular fluid into the lesions. In two control subjects, peroxidase penetration into fibers was seen only rarely and only with other evidence of mechanical injury to the specimen. The findings point to an early and possibly basic abnormality in the plasma membrane of the muscle fiber in Duchenne's dystrophy.

[Desmosomes in invasive laryngeal carcinoma (author's transl)]. / Desmosomen bei invasivem Larynxkarzinom.

The occurrence, morphology, and ultrastructural changes in intercellular desmosomes in squamous cell carcinoma of the larynx was examined by electron miscroscopy. The number of desmosomes in laryngeal carcinomas was decreased as compared to normal epithelia. Structural alterations in the desmosomal components were also observed. Desmosomal structures were also found within the cytoplasm of the malignant keratinocytes. These exhibited the typical features of an intercellular desmosome. These intracytoplasmic desmosomal structures may originate from the cell surface by a process of internalization of desmosome-studded invaginations of the surface membrane. The results indicate that a deficiency of desmosomes may contribute to a loss of the intercellular adhesion, a property which is known to occur in malignant epithelial tumors.