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Different pathways of inositol phosphate metabolism in intact neonatal rat hearts and isolated cardiomyocytes.

ABSTRACT: In most tissues stimulation of the phosphatidylinositol turnover pathway causes release of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], which is subsequently metabolized to a wide range of inositol phosphate isomers deriving from both phosphorylation and dephosphorylation reactions. However, addition of noradrenaline to isolated intact neonatal-rat hearts generated only those inositol phosphates produced by dephosphorylation of Ins(1,4,5)P3. Products of the InsP3 kinase pathway were absent from the profiles, except after prolonged stimulation. In contrast, addition of noradrenaline to isolated cultured neonatal-rat cardiomyocytes caused the release of Ins(1,4,5)P3, which was metabolized by both phosphorylation and dephosphorylation pathways to yield a complex range of inositol phosphate isomers, as observed in many other cell types. These differences between the responses in intact tissues and in isolated cell preparations were not caused by the different conditions used for [3H]inositol labelling. Furthermore, results could not be explained by overgrowth of other cell types in the isolated cell preparations. Thus the results demonstrate that the isolation and culture of rat neonatal cardiomyocytes produces alterations in the nature of the phosphatidylinositol turnover pathway.

SUBMITTER: Woodcock EA

PROVIDER: S-EPMC1130745 | biostudies-other | 1992 Feb

REPOSITORIES: biostudies-other

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Project description:Ischemic post-conditioning (iPoCo) by coronary re-occlusion/reperfusion during immediate reperfusion after prolonged myocardial ischemia reduces infarct size. Mechanical manipulation of culprit lesions, however, carries the risk of coronary microembolization which may obscure iPoCo's cardioprotection. Pharmacological post-conditioning with exogenous triiodothyronine (T3) could serve as an alternative conditioning strategy. Similar to iPoCo, T3 may activate cardioprotective prosurvival pathways. We aimed to study T3's impact on infarct size and its underlying signal transduction. Hearts were isolated from male Lewis rats (200-380 g), buffer-perfused and subjected to 30 min/120 min global zero-flow ischemia/reperfusion (I/R). In additional hearts, either iPoCo (2 × 30 s/30 s I/R) was performed or T3 (100-500 µg/L) infused at reperfusion. Infarct size was demarcated with triphenyl tetrazolium chloride staining and calculated as percent of ventricular mass. Infarct size was reduced with iPoCo to 16 ± 7% vs. 36 ± 4% with I/R only. The maximum infarct size reduction was observed with 300 µg/L T3 (14 ± 2%). T3 increased the phosphorylation of protein kinase B and mitogen extracellular-regulated-kinase 1/2, both key enzymes of the reperfusion injury salvage kinase (RISK) pathway. Pharmacological RISK blockade (RISK-BL) during reperfusion abrogated T3's cardioprotection (35 ± 10%). Adult ventricular cardiomyocytes were isolated from buffer-perfused rat hearts and exposed to 30 min/5 min hypoxia/reoxygenation (H/R); reoxygenation was initiated without or with T3, respectively, and without or with RISK-BL, respectively. Maximal preservation of viability was observed with 500 µg/L T3 after H/R (27 ± 4% of all cells vs. 5 ± 3% in time-matched controls). Again, RISK-BL abrogated protection (11 ± 3%). Mitochondria were isolated at early reperfusion from buffer-perfused rat hearts without or with iPoCo or 300 µg/L T3, respectively, at reperfusion. T3 improved mitochondrial function (i.e.: increased respiration, adenosine triphosphate production, calcium retention capacity, and decreased reactive oxygen species formation) to a similar extent as iPoCo. T3 at reperfusion reduces infarct size by activation of the RISK pathway. T3's protection is a cardiomyocyte phenomenon and targets mitochondria.

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Different pathways of inositol phosphate metabolism in intact neonatal rat hearts and isolated cardiomyocytes.

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