Effect of triamcinolone on parathyroid hormone-stimulated second messenger systems and phosphate transport in opossum kidney cells

Regulation of phosphate uptake in primary cultured rabbit renal proximal tubule cells by glucocorticoids: evidence for nongenomic as well as genomic mechanisms

We have investigated the nongenomic as well as the genomic effects of glucocorticoids on phosphate (Pi) uptake in primary rabbit renal proximal tubule cells (PTCs) and have defined the involved signaling pathways. In the present study, cortisol-BSA (cortisol-BSA) (>10(-9) M, 30 min) was found to inhibit Pi uptake in a time- and concentration-dependent manner. However, progesterone-BSA (P(4)-BSA), 17ss-estradiol-BSA (E(2)-BSA), testosterone-BSA (T(4)-BSA), aldosterone, P(4), E(2), and T(4) (10(-9) M, 1 h) had no effect on Pi uptake. In addition, cortisol-BSA (10(-9) M) did not affect either Na(+) uptake or alpha-methylglucopyranoside (alpha-MG) uptake. The cortisol-BSA-induced inhibition of Pi uptake was associated with a decrease in the V(max) for Pi uptake, rather than the K(m). The inhibitory effect of cortisol-BSA was not blocked either by actinomycin D (an inhibitor of transcription), cycloheximide (an inhibitor of translation), or classical glucocorticoid receptor antagonists (RU 486 or P(4)). The cortisol-BSA-induced inhibition of Pi uptake was blocked by two phospholipase C (PLC) inhibitors (neomycin or U73122), and two protein kinase C (PKC) inhibitors (staurosporine or bisindolylmaleimide I) but not by two adenylate cyclase/protein kinase A inhibitors [SQ 22536 (an adenylate cyclase inhibitor) or myristoylated protein kinase A inhibitor amide 14-22]. Furthermore, cortisol-BSA promoted the translocation of PKC from the cytosolic fraction to the membrane fraction, while having no effect on the activity of adenylate cyclase. Our observations may thus be interpreted as indicating that cortisol does indeed inhibit renal Pi uptake via a nongenomic mechanism, which involves the PLC/PKC pathway.

Stage-specific expression patterns of alkaline phosphatase during development of the first arch skeleton in inbred C57BL/6 mouse embryos

Timing and pattern of expression of alkaline phosphatase was examined during early differentiation of the 1st arch skeleton in inbred C57BL/6 mice. Embryos were recovered between 10 and 18 d of gestation and staged using a detailed staging table of craniofacial development prior to histochemical examination. Expression of alkaline phosphatase is initiated at stage 20.2 in the plasma membrane of mesenchymal cells in the distal region of the first arch. Expression is strongest in osteoid (unmineralised bone matrix) and presumptive periosteum at stage 21.32. Mineralisation begins at stage E23. Expression is present in the mineralised bone matrix. Secondary cartilages form in the condylar and angular processes by stage M24. The cartilaginous cells and surrounding cells in the processes are all alkaline phosphatase-positive and surrounded by the common periosteum, suggesting that progenitor cells of the processes, dentary ramus and secondary cartilages all originate from a common pool. Nonhypertrophied chondrocytes of Meckel's cartilage express alkaline phosphatase at stage M23. Expression in these chondrocytes is preceded by the expression in their adjacent perichondrium. This is true of chondrocytes in all other cranial cartilages examined. 3-D reconstruction of expression in Meckel's cartilage also revealed that the chondrocytes of Meckel's cartilage which express alkaline phosphatase and the matrix of which undergoes mineralisation are those surrounded by the alkaline phosphatase-positive dentary ramus. By stage 25, coincident with mineralisation in the distal section of Meckel's cartilage, most chondrocytes are strongly positive. The perichondria of malleus and incus cartilages express alkaline phosphatase at stage M24. Nonhypertrophied chondrocytes along these perichondria also express alkaline phosphatase. Superficial and deep cells in the dental laminae of incisor and 1st molar teeth become alkaline phosphatase-positive at the bud stage, stages 21.16 and 21.32, respectively. Dental papillae are negative until stage M24 when alkaline phosphatase expression begins in the dental papillae and follicles of the incisor teeth and the dental follicles of the 1st molar teeth. The dental papillae of the 1st molar teeth express alkaline phosphatase at stage 25. Expression in the dental papillae and follicles appears to coincide with cellular differentiation of follicle from papilla. The presumptive squamosal, ectotympanic and gonial membrane bones, lingual oral epithelial cells connected to the dental laminae of the incisor teeth, hair follicle papillae and sheath and surrounding dermis all express alkaline phosphatase in a stage-specific manner.

Abnormalities of parathyroid hormone-mediated signal transduction mechanisms in opossum kidney cells

The second-messengers cAMP, diacylglycerol and inositol 1,4,5-trisphosphate (IP3)-Ca2+ ([Ca2+]i) have been implicated in parathyroid hormone (PTH) receptor-mediated inhibition of sodium/phosphate (Na/P(i)) cotransport across the apical membrane of the proximal tubule. Studies on opossum kidney (OK) cells have been used to study regulatory cascades involved in these PTH actions. In the present study, we further characterized PTH regulatory pathways in two stable mutant cell sublines (J01 and J141) compared to control OK (J09) cells. In J09 cells, addition of PTH resulted in a dose-dependent decrease in Na/P(i) uptake which was associated with an increase in cAMP and cytosolic Ca2+ concentration as well as with activation of protein kinase A, protein kinase C, and MAP kinase. Activation of protein kinase C and of MAP kinase can be detected at PTH concentrations lower than those required for protein kinase A activity. PTH led to similar changes in J01 cells except for the absence of PTH-induced Ca2+ transients. These data confirm the important role of protein kinase C and suggest further that [Ca2+]i transients are not necessary for PTH-mediated inhibition of Na/P(i) cotransport. The J141 subline possessed all of the measured PTH signal pathways but PTH was without effect on Na/P(i) cotransport. The absence of PTH response on Na/P(i) cotransport in J141 cells is likely beyond the PTH-dependent activation of protein kinase A and/or protein kinase C. These studies suggest that Na/P(i) cotransport may be uncoupled from the normal regulatory process. These defined OK cell sublines may be useful in further characterization of PTH action on Na/P(i) cotransport.