The effect of short-wavelength ultraviolet light on antigens, lectin receptors and the ultrastructure of Crithidia fasciculata.

Crithidia fasciculata is an important trypanosomatid parasite commonly affecting insects and is used extensively as a model for the study of the biochemistry, ultrastructure and organization of the kDNA network of trypanosomatids. The present study describes the evolution of UV-induced morphological changes detectable by transmission electron microscopy in Crithidia fasciculata. Although only rare and minor changes in kinetoplast DNA were demonstrable 7 h after UV irradiation, alterations of this organelle were present in almost all flagellates observed 24 h and 48 h after irradiation. Other cell structures were apparently undamaged. Ultrastructural changes in kDNA did not correspond to changes in antigenicity of protein bands in western blotting against serum from Chagas' disease patients or in the presence of 3 different lectin receptors on the surface of the parasite.

Effect of in vivo gamma-irradiation on the binding of wheat germ agglutinin on lymphocyte plasma membranes.

Using quantitative fluorimetry with fluoresceinated wheat germ agglutinin, we have been able to investigate in vivo gamma radiation-induced damage at the outer membrane level of rat splenic lymphocytes, namely damage to the glucosidic moieties of membrane glycoproteins and glycolipids. This paper demonstrates that below an irradiation level of 1 gray (Gy), removal of sialic acid is the major feature leading to new exposed specific binding sites for wheat germ agglutinin, since this lectin is specific for sialic acid and N-acetyl-D-glucosamine. Our studies also suggest that above 1 Gy of irradiation more internal damage occurs, since we observed a striking decrease in wheat germ agglutinin binding sites.

Mobility of voltage-dependent ion channels and lectin receptors in the sarcolemma of frog skeletal muscle.

The mobility of lectin receptors and of two types of ion channels was studied in skeletal muscles of the frog Rana temporaria. Lectin receptors were labeled with fluorescent derivatives of succinyl-concanavalin A (Con A) or wheat germ agglutinin (WGA), and their mobility was measured by fluorescence recovery after photobleaching. Of the receptors for WGA, approximately 53% were free to diffuse in the plane of the membrane, with an average diffusion coefficient as found in other preparations (D = 6.4 X 10(-11) cm2/s). Con A receptors were not measurably mobile. The mobility of voltage-dependent Na and K (delayed rectifier) channels was investigated with the loose-patch clamp method, coupled with through-the-pipette photodestruction of channels by ultraviolet (UV) light. Na channels were not measurably mobile (D less than or equal to 10(-12) cm2/s). With K channels, photodestruction was followed by a small but consistent recovery of K current, which suggested that some K channels diffused in the plane of the membrane. Our results with K currents are best fit if 25% of the K channels diffuse with D = 5 X 10(-11) cm2/s, with the remainder being immobile. For both Na and K channels, photodestruction by UV was most effective at a wavelength of approximately 289 nm. At this wavelength, the energy density required for an e-fold reduction in the number of functional channels was 0.40 J/cm2 for Na channels and 0.94 J/cm2 for K channels. Irradiation at this wavelength and dose did not measurably diminish the mobility of WGA receptors; hence, the immobility of Na and most K channels is not due to UV irradiation. It is concluded that mobile and immobile membrane proteins coexist in the sarcolemma of frog skeletal muscle, and that voltage-dependent Na and K channels are singled out for immobilization.