concanavalin-a and lanthanum-chloride

Topics: Cell Adhesion; Cell Communication; Concanavalin A; Electrophysiology; Energy Metabolism; Erythrocyte Aggregation; Erythrocyte Membrane; Erythrocytes; Humans; Lanthanum; Male; Mathematics; Models, Cardiovascular; Neuraminidase; Osmolar Concentration; Sialic Acids; Surface Properties

Possible involvement of protein kinases in the serotonin (5-HT) transport system in platelets and the inhibitory effect of concanavalin A (Con A) on platelet 5-HT uptake were investigated. Staurosporine and K-252a, highly active inhibitors of protein kinases, did not inhibit 5-HT transport, but they antagonized the inhibitory effect of Con A on 5-HT uptake. KT5720, a protein kinase A inhibitor that has no effect on protein kinase C, neither affected 5-HT transport nor antagonized the inhibitory effect of Con A on 5-HT uptake. The Con A effect on 5-HT uptake was also antagonized by LaCl3, a Ca++ entry blocker. When the activity of Ca++ transport into platelets was estimated, Con A was shown to have a stimulative effect, which was antagonized by alpha-methyl-D-mannoside, a specific antagonist of Con A binding to cell membrane glycoproteins. Furthermore, Con A was shown to stimulate the protein kinase C activity of platelets, which phosphorylates a 40-kDa platelet protein; the Con A effects were antagonized by alpha-methyl-D-mannoside, staurosporine and K-252a, but not by KT5720. We suggest that the activation of protein kinase C and phosphorylation of 40-kDa protein might be involved in the inhibitory effect of Con A on platelet 5-HT transport.

Topics: Alkaloids; Animals; Biological Transport, Active; Blood Platelets; Blood Proteins; Calcium; Calcium Radioisotopes; Carbazoles; Concanavalin A; In Vitro Techniques; Indole Alkaloids; Indoles; Lanthanum; Phosphorylation; Protein Kinase C; Protein Kinase Inhibitors; Protein Kinases; Pyrroles; Rabbits; Serotonin; Staurosporine

A possible regulatory role of calcitonin (CT) upon liver calcium content was investigated by using a Ca2+ channel blocker in thyroparathyroidectomized (TPTX) rats. In bile duct-ligated TPTX rats, liver calcium content was not significantly increased by a single ip injection of calcium chloride (4.0 mg Ca2+/100 g body weight). Administration of CT (80 MRC mU/100 g) caused a remarkable elevation of liver calcium content. This hormonal effect was inhibited by administration of verapamil (1.0 mg/100 g) or lanthanum chloride (0.4 mg/100 g), Ca2+ channel blockers. CT administration markedly increased the transport of calcium into the bile through the liver cells of TPTX rats injected ip with calcium. This increase in the bile calcium content was prevented by administration of verapamil or lanthanum chloride. Administration of epinephrine (10 micrograms/100 g), vasopressin (10 micrograms/100 g), or concanavalin A (1.0 mg/100 g) produced a significant elevation of bile calcium content; these elevations were not significantly altered by addition of verapamil (1.0 mg/100 g). These data suggest the presence of CT receptors on liver cell plasma membranes which are involved in regulation of membrane Ca2+ channels. It is proposed that CT facilitates the entry of extracellular calcium into liver cells by opening Ca2+ channels located on their plasma membranes.

Topics: Animals; Bile Ducts; Calcitonin; Calcium; Concanavalin A; Epinephrine; Ion Channels; Lanthanum; Liver; Male; Parathyroid Glands; Rats; Rats, Inbred Strains; Thyroidectomy; Verapamil