Ruo Hishikawa

Phorbol ester stimulates calcitonin secretion synergistically with A23187, and additively with dibutyryl cyclic AMP in a rat C-cell line.

The mechanism of action of 12-O-tetradecanoyl phorbol-13-acetate (TPA) on calcitonin secretion was studied in a rat C-cell line, rMTC 6-23. TPA stimulated calcitonin secretion at the concentration of 16nM. This effect was synergistically enhanced with calcium ionophore, A23187. Synthetic diacylglycerol, 1-oleoyl-2-acetyl-glycerol (OAG), also showed a synergism with A23187 on calcitonin secretion. When dibutyryl cyclic AMP was added with TPA, an additive effect was obtained. These data suggest that C-kinase might be a possible regulator of calcitonin secretion in addition to the cyclic AMP-mediated pathway.

Effect of calcium channel agonist Bay K 8644 on calcitonin secretion from a rat C-cell line.

Bay K 8644, a novel dihydropyridine, stimulates calcitonin secretion in a dose-dependent manner from a rat medullary thyroid carcinoma cell line, rMTC 6-23, and causes an increase in cytosolic free calcium concentration, as measured by quin-2. These effects are competitively inhibited by nifedipine, and completely abolished in the absence of extracellular calcium. These data suggest that calcium influx via voltage-dependent calcium channels plays a crucial role in the regulation of cytosolic free calcium concentration and calcitonin secretion.

Phorbol esters stimulate phosphate accumulation synergistically with A23187 in cultured renal tubular cells.

The effects of phorbol esters and diacylglycerol on phosphate accumulation in the cultured mouse kidney cells were investigated to assess the possible role of Ca2+-activated, phospholipid dependent protein kinase (protein kinase C) on the renal phosphate handling. 12-O-tetradecanoyl phorbol-13-acetate (TPA) stimulated phosphate accumulation dose-dependently. TPA-induced phosphate accumulation was synergistically enhanced with A23187. 4 alpha-phorbol 12,13-didecanoate did not stimulate the phosphate accumulation, while 4 beta-phorbol 12,13-didecanoate stimulated it. Additionally, 1-oleoyl-2-acetyl-glycerol exhibited a stimulatory effect on phosphate accumulation. These data indicated that protein kinase C is one of possible regulators of phosphate transport at the renal tubules.

A case of membranous lipodystrophy complicated by Fanconi's syndrome

A case of membranous lipodystrophy complicated by Fanconis syndrome is described. A 40-year old man complaining of pain in his legs was admitted to our hospital. Roentgenograms showed cystic changes in the long bones. Biopsy of the affected lesion of the femur revealed a peculiar membranocystic structure in the marrow that is typical of membranous lipodystrophy. He had a neuropsychiatric disorder which is often associated with this disease. Laboratory studies were remarkable for renal proximal tubular dysfunction, i.e., Fanconis syndrome. Membranous lipodystrophy is a rare, hereditary disease that has been reported mainly from Japan and Finland. This is the first case of this disease complicated by Fanconis syndrome. The possible relationship between these disorders is discussed.