The calcium-sensing receptor (CaR) is a G protein-coupled receptor. The CaR stimulation elicits phospholipaseC-mediated inositol triphosphate formation, leading to an elevation in the level of intracellular calcium released from endoplasmicreticulum (ER). Depletion of ER Ca2+ leads to ER stress, which is thought to induce apoptosis. Intracellular calciumoverload-induced apoptosis in cardiac myocytes during hypoxia–reoxygenation (H ?Re) has been demonstrated. However, thelinks between CaR, ER stress and apoptosis during H?Re are unclear. This study hypothesized that the CaR could induceapoptosis in neonatal rat cardiomyocytes during H?Re via the ER stress pathway. Neonatal rat cardiomyocytes were subjectedto 3 hr of hypoxia, followed by 6 hr of reoxygenation. CaR expression was elevated and the number of apoptotic cells wassignificantly increased, as shown by transferase-mediated dUTP nick end-labelling, with exposure to CaCl2, a CaR activator,during H?Re. The intracellular calcium concentration was significantly elevated and the Ca2+ concentration in the ER wasdramatically decreased during H?Re with CaCl2; both intracellular and ER calcium concentrations were detected by laserconfocal microscopy. Expression of GRP78 (glucose-regulated protein 78), the cleavage products of ATF6 (activating transcriptionfactor 6), phospho-PERK [pancreatic ER kinase (PKR)-like ER kinase], the activated fragments of caspase-12, andphospho-JNK (c-Jun NH2-terminal kinase) were increased following exposure to CaCl2 during H?Re. Our results confirmedthat the activated CaR can induce cardiomyocyte apoptosis via ER stress-associated apoptotic pathways during H? Re.

Cardiac hypertrophy is a common pathological change accompanying cardiovascular disease. Recently, some evidence indicated thatcalcium-sensing receptor (CaSR) expressed in the cardiovascular tissue. However, the functional involvement of CaSR in cardiac hypertrophyremains unclear. Previous studies have shown that CaSR caused accumulation of inositol phosphate to increase the release ofintracellular calcium. Moreover, Ca2+-dependent phosphatase calcineurin (CaN) played a vital role in the development of cardiac hypertrophy.Therefore, we investigated the expression of CaSR in cardiac hypertrophy-induced by angiotensin II (AngII) and the effects ofCaSR activated by GdCl3 on the related signaling transduction pathways. The results showed that AngII induced cardiac hypertrophyand up-regulated the expression of CaSR, meanwhile increased the intracellular calcium concentration ([Ca2+]i) and activated CaNhypertrophic signaling pathway. Compared with AngII alone, the above changes were further obvious when adding GdCl3. But theeffects of GdCl3 on the cardiac hypertrophy were attenuated by CsA, a specific inhibitor of CaN. In conclusion, these results suggestthat CaSR is involved in cardiac hypertrophy-induced by AngII through CaN pathway in cultured neonatal rat cardiomyocytes.

1. Acute myocardial infarction (AMI) is strongly associatedwith atherosclerosis, and is responsible for significant morbidityand mortality worldwide. The pathogenic mechanisms thatunderlie atherosclerosis and AMI are undefined at present. Thecalcium-sensing receptor (CaSR) is a member of the superfamilyof G-protein coupled receptors. It has been demonstrated previouslythat the expression of CaSR is increased in atheroscleroticcardiac tissue of rats. It has also been suggested that CaSR has acrucial role in cardiac ischaemia–reperfusion injury, apoptosisand hypertrophy. However, it remains to be determined whetheran increase in the expression of CaSR influences the sensitivity ofcardiomyocytes to AMI.2. The present study used cultured ventricular cardiomyocytesfrom neonatal rats to investigate the effect of oxidized low-densitylipoprotein (ox-LDL), ischaemia–reperfusion, GdCl3 (an agonistof CaSR) and NPS-2390 (an antagonist of CaSR) on the expressionof CaSR. The amount of apoptosis, alterations in the morphologyof the cells, the intracellular calcium concentration([Ca2+]i) and components of critical mitochondrial pathwayswere also analysed.3. Cardiomyocytes treated with ox-LDL showed upregulatedexpression of CaSR, cytochrome c (cyt-c), Bax and activated caspase3 (17 kD) and downregulated expression of Bcl-2, as well aselevated [Ca2+]i and apoptosis. Application of GdCl3 augmentedthese effects, and NPS-2390 decreased the expression of CaSRand reduced apoptosis.4. In conclusion, ox-LDL was found to increase the expressionof CaSR in a manner that was dependent on time anddose. It also augmented apoptosis during simulated ischaemia-reperfusion in cultured ventricular cardiomyocytes fromneonatal rats.

Polyamines (putrescine, spermidine, and spermine)play an essential role in cell growth, differentiation, andapoptosis. Protein kinase C (PKC) stimulates polyaminebiosynthesis through the induction of ornithine decarboxylase(ODC), a rate-limiting enzyme in polyaminebiosynthesis. Activation of PKC mediates ischemic preconditioningto reduce necrosis and apoptosis in intacthearts and in isolated culture cardiomyocytes. In this study,we examined whether the ODC/polyamine system isinvolved in the ischemic preconditioning signaling pathwayand whether this system interacts with PKC inpreconditioning-induced cardioprotection. Hearts werepreconditioned with three cycles of 5-min ischemia and5-min reflow, which caused an increase of ODC expressionand spermidine, spermine, and total polyamine pool levels.a-Difluoromethylornithine (DFMO) and ethylglyoxal bis(guanylhydrazone) (EGBG) inhibited the key enzymesinvolved in polyamine biosynthesis, and abolished thepreconditioning-induced reduction in infarct size andimprovement in postischemic heart contractility function.They also increased cell apoptosis extent and aggravatedmyocardium ultrastructure damage. Inhibition also attenuatedthe preconditioning-induced translocation and activationof the PKC-d,-e isoforms from the cytosol to theparticulate. Conversely, activation of PKC by phorbol 12-myristate 13-acetate (PMA) upregulated the ODC/polyaminesystem, whereas the PKC inhibitor chelerythrine(Che) downregulated the ODC/polyamine system. Thesefindings suggest that upregulation of the polyamine synthesismetabolism occurs in response to preconditioningand mediates preconditioning-induced cardioprotection.The ODC/polyamine system and PKC signals may "crosstalk" in preconditioned hearts such that inhibiting onepathway leads to a reduction in the activity of the otherpathway and vice versa.

1. Myocardial hypertrophy is a common pathologicalchange that accompanies cardiovascular disease. Dopamine D2receptors have been demonstrated in cardiovascular tissues.However, the pathophysiological involvement of D2 receptorsin myocardial hypertrophy is unclear. Therefore, the effects ofthe D2 receptor agonist bromocriptine and the D2 receptorantagonist haloperidol on angiotensin (Ang) II-or endothelin(ET)-1-induced hypertrophy of cultured neonatal rat ventricularmyocytes were investigated in the present study.2. Protein content and protein synthesis, determined byexamining [3H]-leucine uptake, were used as estimates of cardiomyocytehypertrophy. The expression of D2 receptor proteinin neonatal rat ventricular myocytes was determined usingwestern blotting. Changes in [Ca2?]i in cardiomyocytes wereobserved by laser scanning confocal microscopy.3. Angiotensin II and ET-1, both at 10 nmol/L, inducedmyocyte hypertrophy, as demonstrated by increased proteincontent and synthesis, [Ca2?]i levels, protein kinase C (PKC)activity and phosphorylation of extracellular signal-regulatedkinase, c-Jun N-terminal kinase and mitogen-activated proteinkinase (MAPK) p38 (p38). Concomitant treatment of cells with10 nmol/L AngII plus 10mol/L bromocriptine significantlyinhibited cardiomyocyte hypertrophy, MAPK phosphorylationand PKC activity in the membrane, as well as [Ca2?]i signallingpathways, compared with the effects of AngII alone. In addition, 10 mol/L bromocriptine significantly inhibited cardiomyocytehypertrophy induced by 10 nmol/L ET-1. However, pretreatmentwith haloperidol (10mol/L) had no significant effects oncardiomyocyte hypertrophy induced by either AngII or ET-1.4. In conclusion, D2 receptor stimulation inhibits AngIIinducedhypertrophy of cultured neonatal rat ventricularmyocytes via inhibition of MAPK, PKC and [Ca2?]i signallingpathways.