Uptake and binding of prostaglandins in a marine bivalve, Modiolus demissus

Abstract

The existence of specific PGA2 binding sites was demonstrated in the 12,000 x g supernatant fraction of homogenized gill tissue from Modiolus demissus (Geukensia demissus). The binding of prostaglandins at these sites was pH-dependent, time-dependent, and reversible. The binding was more specific for prostaglandin A2 (PGA,) than prostaglandin E2 (PGE2) or prostaglandin F2. (PGF,,). Binding was enhanced by calcium and magnesium. For calcium the binding kinetics exhibited a K, of 7 mM; for magnesium the K, was 15 mM. The amount of PGA2 bound/mg protein at saturating cation concentration was determined to be 0.20 pmoles/mg for both calcium and magnesium. A dissociation constant (Kd) of 9.8 x M was calculated by Scatchard plot analysis for the PGA2 binding site. Binding was inhibited by 20 mM Cu++, M ATP and M GTP. These low-affinity binding sites may perform an important role in the physiological action of prostaglandins in marine bivalves.Marine bivalves take up prostaglandins from the surrounding seawater (Bito, '72a). These animals also synthesize prostaglandins (Freas and Grollman, '80). In gill tissue from Modiolus demissus (Geukensia demissus) synthesis of prostaglandin E2 (PGE,) is dependent on the ionic and osmotic state of the surrounding seawater (Freas and Grollman, '80). Also, the pharmacological addition of PGE, to seawater increases the in vitro uptake of 45calcium by this tissue (Freas, '78). In freshwater bivalves PGE2 inhibits sodium transport (Graves and Dietz, '79). Therefore, the uptake and binding of prostaglandins was investigated in Modiolus demissus gill tissue in order to determine a physiological role for these compounds in marine bivalves. Although prostaglandin receptors have been identified in numerous mammalian tissues (reviewed by Samuelsson et al., '75), their presence in invertebrate tissue has not been established.Unlike mammalian tissue, some invertebrate tissues, most notably the gorgonian Plexaura homomalla, contain high concentrations of prostaglandin A2 (PGA,) (Light and Samuelsson, '72). The object of this research is to determine if PGE or PGA binding sites are present in Modiolus demissus, and if they are, to determine their binding characteristics. MATERIALS AND METHODS Animals and reagentsSpecimens of Modiolus demissus were collected and maintained as previously described (Freas and Grollman, '80). Labeled prostaglandins were obtained from New England Nuclear. Their purity was periodically checked and if necessary, they were repurified by thinlayer chromatography (Ramwell and Daniels, '69). Labeled prostaglandins used were prostaglandin A2 [5,6,8, 11 ,12,14, prostaglandin Al [5,6, prostaglandin E2[5,6,8,11,12,14,

Carbocyclic oxylipins of marine origin

“…A lowaffinity PGA2 binding site has been described from M. demissus. 69 The red alga Gracilaria verrucosa was a source of small amounts of PGA2 ( 16); however, this may be a dehydration artifact of the more major metabolite in the alga, PGE2 (14, see above).26 Proposed biosynthesis of (15f? )-prostaglandin A2 (33) by the Caribbean octocoral Plexaura homomalla (from ref 5).…”

“…A number of derivatives of these clavulone natural products have subsequently been isolated from C. viridis and defined using similar techniques, including the 20acetoxy derivatives of clavulones I-III (63-65),80 CIO chlorine-containing metabolites chlorovulones I-IV (66)(67)(68)(69),'75)81 the bromo and iodo analogs (70 and 71) of chlorovulone I,82 and the CIO,11-epoxide analog of chlorovulone I (72) . 83 The biosynthesis of these C. viridis prostanoids has been the source of intense interest and experimentation.…”

A novel multifunctional metabolic pathway in a marine mollusc leads to unprecedented prostaglandin derivatives (prostaglandin 1,15-lactones)

“…After the first report of PGs in an invertebrate organism, the gorgonian coral Plexaura homomalla (Weinheimer & Spraggins, 1969), evidence obtained using techniques such as mammalian smooth muscle bioassays, radioimmunoassays and labelled arachidonic acid (AA) incorporation experiments has led to the suggestion that prostanoids are present in, for example, the freshwater mussel Ligunia subrostrata (Saintsing et al, 1983), the freshwater snail Heliosoma durgi (Kunigelis & Saleuddin, 1986), the mussel Mytilus californianus (Morse et al, 1977) and several coelenterates (Morse et al, 1978). Specific PGA2 binding sites were detected in homogenates of gills, mantle, siphon, adductors, and upper and lower visceral masses from the marine bivalve Modiolus demissus (Freas & Grollman, 1981). However, the structures of the eicosanoids involved were elucidated completely in only a few cases, and usually evidence of eicosanoid participation was based on treatment of specimens with a single compound and observation of the response.…”

A specific prostaglandin E2 receptor and its role in modulating salivary secretion in the female tick, Amblyomma americanum (L.)

“…An exception is a receptor of a prostaglandin A2 iri the gill tissue of a marine bivalve Modiolus demissus (Freas and Grollman, 1981 ). Since PGE2 has been found to play a role in modulating tick salivary secretion, it is possible that the binding of PGE2 to a specific receptor may be the initial step leading to its physiological action on the tissue.…”