ABSTRACT
Intracellular exchangeable calcium and calcium efflux were investigated in cultured amoebocytes of land snails. Low extracellular calcium concentration (0.32 mM) initiated a rapid increase of outward calcium currents and decrease of intracellular exchangeable calcium. On the other hand, high extracellular calcium concentration (32 mM) increased intracellular exchangeable calcium. Actions of vitamin D metabolites were most prominent under non-physiological concentrations of extracellular calcium. Metabolite E activated a calcium pump while 25-hydroxy-vitamin D3 deactivated the pump. Both metabolites increased calcium transfer into stored pools.
Subject(s)
Calcifediol/pharmacology , Calcitriol/pharmacology , Calcium Channels/metabolism , Calcium/metabolism , Hemocytes/metabolism , Animals , Calcium/pharmacology , Calcium Channels/drug effects , Cytoplasmic Granules/drug effects , Cytoplasmic Granules/metabolism , Hemocytes/drug effects , In Vitro Techniques , Kinetics , Snails , Time FactorsABSTRACT
Calcium is one of the most important substances affecting the life of molluscs, and vitamin D was shown to be an essential nutrient for land snails. In an attempt to elucidate the role that vitamin D plays in calcium metabolism of land snails, we have developed a procedure for the isolation of specialized calcium cells from digestive gland of land snails, and were able to culture these cells. The effect of vitamin D metabolites on the intracellular exchangeable calcium and alkaline phosphatase activity was studied. The metabolites tested were 25-hydroxycholecalciferol (25(OH)D3), 24,25-dihydroxycholecalciferol (24,25(OH)2D3), 1,25-dihydroxycholecalciferol (1,25(OH)2D3), and the molluscan metabolite E. 25(OH)D3 was found to be the most active sterol in elevating intracellular exchangeable calcium and the activity of alkaline phosphatase, and the molluscan metabolite E was found to be the most potent sterol in the suppression of alkaline phosphatase activity. 1,25(OH)2D3 was shown to suppress both activities at high concentrations, and 24,25(OH)2D3 increased the intracellular exchangeable calcium only at high concentrations. Thus, 25(OH)D3 which is regarded as a storage form of vitamin D and devoid of biological activity, seems to be biologically active in invertebrates.
Subject(s)
Calcium/analysis , Digestive System/chemistry , Digestive System/cytology , Snails/metabolism , Vitamin D/pharmacology , 24,25-Dihydroxyvitamin D 3/metabolism , 24,25-Dihydroxyvitamin D 3/pharmacology , Alkaline Phosphatase/physiology , Animals , Calcitriol/metabolism , Calcitriol/pharmacology , Calcium/metabolism , Cells, Cultured , Digestive System/metabolism , Vitamin D/metabolismABSTRACT
The effect of 24,25-dihydroxyvitamin D3 on some of the activities of 1,25-dihydroxyvitamin D3 was studied in cultures of cartilage cells obtained from the tibial growth plate of rachitic chicks. The activities that were tested are those associated with intracellular exchangeable calcium, alkaline-phosphatase activity and the incorporation of thymidine and proline. 24,25-dihydroxyvitamin D3 was shown in this system to antagonize the suppressive effect of 1,25-dihydroxyvitamin D3 on intracellular exchangeable calcium and on proline incorporation. A similar effect on alkaline phosphatase activity and thymidine incorporation was not observed.
