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Original Articles
- Role of Protein kinase C in Desensitization of Somatostatin-induced Calcium Signalling in NG108-15 Cells.
- Kyoung Mi Kim, Jong Ho Sung, Myung Jun Kim, Duck Joo Rhie, Yang Hyeok Jo, Sang June Hahn, Myung Suk Kim, Shin Hee Yoon, Bu Seung Kim
- J Korean Endocr Soc. 2005;20(4):353-361. Published online August 1, 2005
- DOI: https://doi.org/10.3803/jkes.2005.20.4.353
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Abstract
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Activation of G-protein coupled-somatostatin receptors induces the release of calcium from inositol 1, 4, 5-trisphosphate-sensitive intracelluar stores. G-protein-coupled receptor signaling decreases with prolonged exposure to an agonist. SEBJECTS and METHODS: Fura-2-based digital Ca2+ imaging was used to study the effects of prolonged exposure to an agonist on the somatostatin-induced intracellular Ca2+ concentration([Ca2+]i) increases in NG108-15 cells, which were differentiated with CO2-independent medium and 10micrometer forskolin. RESULTS: Exposure to somatostatin(1micrometer) for 30 min completely desensitized the NG108-15 cells to a second somatostatin-induced response. The cells recovered gradually over 20 min following washout of the somatostatin. The desensitization was not due to depletion of the intracellular Ca2+ stores, and pretreatment for 30 min with bradykinin(100nM), which activates phospholipase C, or DADLE(D-Ala2-D-Leu5 enkephalin, 1microM), which activates phospholipase C, failed to cross-desensitize the somatostatin-evoked [Ca2+]i increases. Treatment with 8-cpt-cAMP(0.1mM) for 30min did not influence the somatostatin-induced[Ca2+]i increases. Phorbol 12, 13-dibutyrate(PdBu, 1microM) blocked the response completely. Down-regulation of PKC due to 24 h exposure of PdBu (1microM) inhibited the somatostatin-induced desensitization. CONCLUSION: Prolonged exposure of somatostatin to NG108-15 cells desensitized the somatostatin-induced release of Ca2+ from the intracelluar store, with protein kinase C also involved in the desensitization.
- Crosstalk Between cAMP and Phosphoinositide System in Signal Transduction Pathways Through TSH Receptor.
- Byung Sool Moon, Young Joo Park, Seong Yeon Kim, Bo Youn Cho, Hong Kyu Lee, Do Joon Park
- J Korean Endocr Soc. 2003;18(4):404-413. Published online August 1, 2003
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Abstract
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- BACKGROUND
TSH stimulates both the adenyl cyclase and phospholipase C (PLC) pathways by binding to a single cell surface receptor that is coupled to G protein, and we examined crosstalk between these two signaling pathways. METHODS: FRTL-5 rat thyroid cells were grown in 6H medium, then incubated with 5H medium before the stimulation. Then cells were incubated for 24 hours with 5H mix containing 1 mCi/L myo-(2-N-3H) inositol. After pretreatment of 100 microM Rp-cAMP, 100 microM forskolin, 50 nM staurosporine, or 100 nM PMA (phorbol-12-myristate-13-acetate), TSH were added in different experiments. After 30 min at 37 degrees C, cells were disrupted and IP formation was determined. RESULTS: Stimulation with 100 microU/mL TSH resulted in a 1.65 fold increase in IP generation. In pursuing the possibility that the two post-receptor events might be linked in some way, we examined the effect of exogenously administrated Rp-cAMP, protein kinase A antagonist, and forskolin, a direct stimulant of protein kinase A, on IP generation achieved at a dose of 100 microU/mL TSH. The pretreatment of 100 M Rp-cAMP at a concentration sufficient to inhibit protein kinase A enhanced TSH-induced IP production. This effect of Rp-cAMP was dose-dependent. Forskolin attenuatedTSH-stimulated increases in phosphatidylinositide turnover. PMA, a protein kinase C (PKC) activator and staurosporine, a PKC inhibitor did not affect TSH-induced IP generation. CONCLUSION: These data suggested that activation of adenylate cyclase/cAMP post-receptor signalling casacde, which results in the protien kinase A activation, has an inhibitory effect on IP turnover activated by TSH.
- Mechanism of Angiotensin 2-Stimulated Aldosterone Secretion in Adrenal Glomerulosa Cells of Diabetic Rats ; Normal Phospholipase Activity and Intracellular Calcium Mobilization.
- Yeon Ah Sung, Nan Ho Kyung
- J Korean Endocr Soc. 1997;12(2):230-244. Published online January 1, 2001
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Abstract
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- BACKGROUND
Diabetic patients develop hypoaldosteronism which frequently caused hyperkalemia and metabolic acidosis and diabetic hypoaldosteronism is associated with selective unresponsiveness of aldosterone to angiotensin A-II, but mechanism of defect in A-II stimulated aldosterone response still remain unclear. METHODS: To elucidate the mechanism of defect in A-II stimulated aldosterone response, author evaluated the responses of aldosterone production to A-II, K+, and ACTH in adrenal glomerulosa cells prepared from streptozotocin induced diabetic rats, Inositol triphosphate (IP3) generated by activation of phospholipase C (PLC) and arachidonic acid and lysophospholipids generated by activation of phospholipase A2 (PLA2) were measured in A-II stimulated glomerulosa cells. Radiocalcium efflux and aldosterone response to second messenger of A-II such as PLC, IP3, PLA, AA and protein kinase C activator, 12-o-tetradecanoylphorbol 13 acetate (TPA). RESULTS: 1. Plasma renin activity and aldosterone levels were not different among control rats, untreated and insulin treated diabetic rats. 2. Basal, ACTH and K+ -stimulated aldosterone production were similar in cells from the three groups (p<0.05), but A-II stimulated aldosterone production was significantly decreased in cells from untreated diabetic rats compared with control and insulin treated diabetic rats (p
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