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- Komai, Ali, 1987, et al.
(författare)
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PKA-independent cAMP stimulation of white adipocyte exocytosis and adipokine secretion: Modulations by Ca2+ and ATP
- 2014
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Ingår i: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 592:23, s. 5169-5186
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Tidskriftsartikel (refereegranskat)abstract
- We examined the effects of cAMP, Ca2+ and ATP on exocytosis and adipokine release in white adipocytes by a combination of membrane capacitance patch-clamp recordings and biochemical measurements of adipokine secretion. 3T3-L1 adipocyte exocytosis proceeded even in the complete absence of intracellular Ca2+ ([Ca2+]i; buffered with BAPTA) provided cAMP (0.1 mm) was included in the intracellular (pipette-filling) solution. Exocytosis typically plateaued within ~10 min, probably signifying depletion of a releasable vesicle pool. Inclusion of 3 mm ATP in combination with elevation of [Ca2+]i to ≥700 nm augmented the rate of cAMP-evoked exocytosis ∼2-fold and exocytosis proceeded for longer periods (≥20 min) than with cAMP alone. Exocytosis was stimulated to a similar extent upon substitution of cAMP by the Epac (exchange proteins activated by cAMP) agonist 8-Br-2′-O-Me-cAMP (1 mm included in the pipette solution). Inhibition of protein kinase A (PKA) by addition of Rp-cAMPS (0.5 mm) to the cAMP-containing pipette solution was without effect. A combination of the adenylate cyclase activator forskolin (10 μm) and the phosphodiesterase inhibitor IBMX (200 μm; forsk-IBMX) augmented adiponectin secretion measured over 30 min 3-fold and 2-fold in 3T3-L1 and human subcutaneous adipocytes, respectively. This effect was unaltered by pre-loading of cells with the Ca2+ chelator BAPTA-AM and 2-fold amplified upon inclusion of the Ca2+ ionophore ionomycin (1 μm) in the extracellular solution. Adiponectin release was also stimulated by the membrane-permeable Epac agonist 8-Br-2′-O-Me-cAMP-AM but unaffected by inclusion of the membrane-permeable PKA inhibitor Rp-8-Br-cAMPS (200 μm). The adipokines leptin, resistin and apelin were present in low amounts in the incubation medium (1-6% of measured adiponectin). Adipsin was secreted in substantial quantities (50% of adiponectin concentration) but release of this adipokine was unaffected by forsk-IBMX. We propose that white adipocyte exocytosis is stimulated by cAMP/Epac-dependent but Ca2+- and PKA-independent release of vesicles residing in a readily releasable pool and that the release is augmented by a combination of Ca2+ and ATP. We further suggest that secreted vesicles chiefly contain adiponectin.
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| 2. |
- Åström-Olsson, Karin, 1959, et al.
(författare)
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Impact of hypoxia, simulated ischemia and reperfusion in HL-1 cells on the expression of FKBP12/FKBP12.6 and intracellular calcium dynamics
- 2012
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Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 422:4, s. 732-738
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Tidskriftsartikel (refereegranskat)abstract
- Aims: To establish a cardiac cell culture model for simulated ischemia and reperfusion and in this model investigate the impact of simulated ischemia and reperfusion on expression of the calcium handling proteins FKBP12 and FKBP12.6, and intracellular calcium dynamics. Methods: HL-1 cell cultures were exposed to normoxia (as control), hypoxia, simulated ischemia (HEDA) or HEDA + reactive oxygen species (ROS) for up to 24 h and after HEDA, with or without ROS, followed or not by simulated reperfusion (REPH) for 6 h. Viability was analyzed with a trypan blue exclusion method. Cell lysates were analyzed with real-time PCR and Western blot (WB) for FKBP12 and FKBP12.6. Intracellular Ca(2+)measurements were performed using dual-wavelength ratio imaging in fura-2 loaded cells. Results: A time-dependent drop in viability was shown after HEDA (P < 0.001). Viability was not further influenced by addition of ROS or REPH. The general patterns of FKBP12 and FKBP12.6 mRNA expression showed upregulation after hypoxia, downregulation after ischemia and normalization after reperfusion, which was partially attenuated if ROS was added during HEDA. The protein contents were unaffected after hypoxia, tended to increase after ischemia and, for FKBP12.6, a further increase after reperfusion was shown. Hypoxia or HEDA, with or without REPH, resulted in a decreased amplitude of the Ca2+ peak in response to caffeine. In addition, cells subjected to HEDA for 3 h or HEDA for 3 h followed by 6 h of REPH displayed irregular Ca2+ oscillations with a decreased frequency. Conclusion: A threshold for cell survival with respect to duration of ischemia was established in our cell line model. Furthermore, we could demonstrate disturbances of calcium handling in the sarcoplasmic reticulum as well as alterations in the expressions of the calcium handling proteins FKBP12 and FKBP12.6, why this model may be suitable for further studies on ischemia and reperfusion with respect to calcium handling of the sarcoplasmic reticulum. (C) 2012 Elsevier Inc. All rights reserved.
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