RESUMEN
Vesicles derived from the endoplasmic reticulum of sea cucumber smooth muscle retain a membrane bound Ca(2+)-ATPase that is able to transport Ca(2+) into the vesicles at the expense of ATP hydrolysis. In contrast with vesicles obtained from rabbit muscles, the activity of the Ca(2+)-dependent ATPase from sea cucumber is dependent on monovalent cations (K(+)>Na(+)>Li(+)). With the addition of highly sulfated polysaccharide to vesicle preparations from rabbit muscle, Ca(2+) uptake decreases sharply and becomes highly sensitive to monovalent cations, as observed with vesicles from sea cucumber muscle. These results led us to investigate the possible occurrence of a highly sulfated polysaccharide on vesicles from the endoplasmic reticulum of sea cucumber smooth muscle, acting as an "endogenous" Ca(2+)-ATPase inhibitor. In fact, vesicles derived from the invertebrate, but not from rabbit muscle, contain a highly sulfated polysaccharide. This compound inhibits Ca(2+) uptake in vesicles obtained from rabbit muscle and the inhibition is antagonized by monovalent cation. In addition, sea cucumber muscles contain high concentrations of another polysaccharide, which surrounds the muscle fibers, and was characterized as a fucosylated chondroitin sulfate. Possibly the occurrence of sulfated polysaccharides in the sea cucumber muscles is related with unique properties of the invertebrate body wall, which can rapidly and reversibly alter its mechanical properties, with change in length by more than 200%.
Asunto(s)
ATPasas Transportadoras de Calcio/antagonistas & inhibidores , Inhibidores Enzimáticos/farmacología , Músculo Liso/química , Polisacáridos/farmacología , Animales , Calcio/metabolismo , Inhibidores Enzimáticos/aislamiento & purificación , Transporte Iónico , Peso Molecular , Músculo Liso/metabolismo , Polisacáridos/química , Polisacáridos/aislamiento & purificación , Potasio/metabolismo , Conejos , Retículo Sarcoplasmático/química , Retículo Sarcoplasmático/metabolismo , Pepinos de Mar , Sodio/metabolismo , Ácidos Sulfúricos/químicaRESUMEN
Dermatan sulfates with the same backbone structure [4-alpha-L-IdceA-1-->3-beta-D-GalNAc-1]n but with different patterns of sulfation substitutions have been isolated from the ascidian body. All the ascidian dermatan sulfates have a high content of 2-O-sulfated alpha-L-iduronic acid residues but differ in the pattern of sulfation of the N-acetyl-beta-D-galactosamine units. Styela plicata and Halocynthia pyriformis have 4-O-sulfated units, but in Ascidian nigra they are 6-O-sulfated. This collection of ascidian dermatan sulfates (together with native and oversulfated mammalian dermatan sulfate), where the extent and position of sulfate substitution have been fully characterized, were tested in anticoagulant assays. Dermatan sulfate from A. nigra has no discernible anticoagulant activity, which indicates that 4-O-sulfation of the N-acetyl-beta-D-galactosamine is essential for the anticoagulant activity of this glycosaminoglycan. In contrast dermatan sulfates from S. plicata and H. pyriformis are potent anticoagulants due to potentiation of thrombin inhibition by heparin cofactor II. These ascidian dermatan sulfates have approximately 10-fold and approximately 6-fold higher activity with heparin cofactor II than native and an oversulfated mammalian dermatan sulfate, respectively. They have no effect on thrombin or factor Xa inhibition by antithrombin. These naturally oversulfated ascidian dermatan sulfates are sulfated at selected sites required for interaction with heparin cofactor II and thus have specific and potent anticoagulant activity.