Biomedical subjects

Hans Michael Piper

Publications and source records attributed to Hans Michael Piper.

23 records · Page 2Linked to original sources

PubMed2003

Reoxygenation-induced rigor-type contracture.

The hypothesis tested was that reoxygenation-induced contracture of myocardial cells, a form of reperfusion injury, can be due to a rigor-type mechanism. Isolated adult cardiomyocytes were exposed to 30- or 60-min anoxia (pH 6.4) and reoxygenation (pH 7.4). In cardiomyocytes, cytosolic Ca(2+) and cell length, and in isolated rat hearts left ventricular end-diastolic pressure (LVEDP) were measured. During reoxygenation, cardiomyocytes developed contracture. When energy recovery was slowed down, less Ca(2+) overload was required for contracture: (1) after 30-min anoxia Ca(20) (cytosolic Ca(2+) concentration in cells with 20% cell length reduction) was 1.42 +/- 0.11 micromol/l; (2) after 30-min anoxia with partial mitochondrial inhibition during reoxygenation (NaCN, 0.1 mmol/l) Ca(20) was reduced to 0.69 +/- 0.05 micromol/l; (3) after 60-min anoxia Ca(20) was reduced to 0.78 +/- 0.05 micromol/l and (4) when energy recovery was accelerated (succinate, 0.2 mmol/l), Ca(20) rose to 1.35 +/- 0.05 micromol/l. In isolated hearts, the reperfusion-induced rise in LVEDP was modulated by the same interventions. Slow recovery of energy production favors reoxygenation-induced contracture in cardiomyocytes and hearts. This shows that rigor contracture contributes to reoxygenation-induced cell injury.

Animals↗

PubMed2002

Inhibition of apoptotic responses after ischemic stress in isolated hearts and cardiomyocytes.

Recent findings on the induction of anti-apoptotic gene expression in ischemic/reperfused hearts encouraged us to investigate whether ischemic/reperfused hearts may be protected against apoptosis induction. To analyze this hypothesis we performed studies on isolated perfused hearts of rat. For apoptosis induction, hearts were perfused with the NO donor (+/-)-S-nitroso-N-acetylpenicillamine (SNAP, 10 microM) for 30 minutes. Four hours thereafter apoptosis was detected by DNA laddering and TUNEL assay. Under normoperfusion SNAP induced 5.5 +/- 1.4 TUNEL-positive myocytes per tissue section (vs. 1.8 +/- 0.5 in controls). But when hearts were subjected to 20 minutes of no flow ischemia, which was sufficient for energy depletion of the hearts without inducing severe necrotic or apoptotic cell death, reperfusion in the presence of SNAP did not induce apoptosis. To analyze if this mode of protection is a property of the cardiomyocytes, we performed corresponding experiments on ventricular cardiomyocytes of rat. Again, under normoxic conditions SNAP (100 (microM) increased the number of TUNEL-positive cells to 12.6 +/- 4.9 % (vs. 5.4 +/- 0.7 % in controls). But when SNAP was added after 3 h of simulated ischemia, which was sufficient for energy depletion of the cells without inducing apoptotic cell death, the number of apoptotic cells did not increase. The ischemia-induced protection of hearts and cardiomyocytes goes along with an increased expression of several anti-apoptotic genes, mainly of the bcl-2 family. This indicates that ischemic conditions induce an anti-apoptotic gene program in cardiomyocytes, which may also be responsible for the observed anti-apoptotic actions in the intact ischemic/reperfused myocardium.

Animals↗

PubMed2002

Neuropeptide Y modifies the hypertrophic response of adult ventricular cardiomyocytes to norepinephrine.

OBJECTIVE: The hypertrophic response of adult rat cardiomyocytes to norepinephrine via alpha-adrenoceptor stimulation is limited by an inhibitory cross-talk of simultaneously beta-adrenoceptor stimulation. On the other hand, neuropeptide Y (NPY), known to be co-secreted with norepinephrine from intramural nerve endings of the heart, exerts an anti-beta-adrenergic effect. Therefore, it should be expected that NPY enhances the hypertrophic response to norepinephrine. This hypothesis was addressed in the present study. METHODS: Isolated adult ventricular cardiomyocytes from rats were used. As parameters of hypertrophic growth we investigated cell volume, cross-sectional area, protein mass. Protein and RNA synthesis were determined by incorporation of [(14)C]phenylalanine or [(14)C]uridine, respectively. RESULTS: Norepinephrine (1 micromol/l) did not significantly increase protein or RNA synthesis. In co-presence of NPY (100 nmol/l), however, norepinephrine increased protein synthesis by 44% and RNA synthesis by 18%. Under the same conditions, NPY enhanced the effect of norepinephrine on cell volume from +6.4 to +18.2%, its effect on cross-sectional area from +16 to +23%, and increased the protein/DNA ratio from 32.5 to 35.6 mg/mg. In parallel, norepinephrine caused a translocation of PKC-alpha and PKC-delta into the particular fractions and this effect of norepinephrine was also enhanced by co-presence of NPY. In contrast, NPY did not enhance ERK-activation caused by norepinephrine. CONCLUSION: Our study indicates the anti-beta-adrenergic effect of NPY is sufficient to modulate the hypertrophic response of adult ventricular cardiomyocytes to norepinephrine. The results suggest that the hypertrophic effect of norepinephrine via alpha-adrenoceptor stimulation can be modulated by co-release of NPY from intramural nerve endings.

Animals↗

PubMed2002

Effect of inhibition of Na(+)/Ca(2+) exchanger at the time of myocardial reperfusion on hypercontracture and cell death.

OBJECTIVE: There is recent evidence that Ca(2+) influx via reverse mode Na(+)/Ca(2+) exchange (NCX) at the time of reperfusion can contribute to cardiomyocyte hypercontracture. However, forward NCX is essential for normalization of [Ca(2+)](i) during reperfusion, and its inhibition may be detrimental. This study investigates the effect of NCX inhibition with KB-R7943 at the time of reperfusion on cell viability. METHODS: The effect of several concentrations of KB-R7943 added at reperfusion was studied in Fura-2 loaded quiescent cardiomyocytes submitted to 40 min of simulated ischemia (NaCN 2 mM, pH 6.4), and in rat hearts submitted to 60 min of ischemia. [Ca(2+)](i) and cell length were monitored in myocytes, and functional recovery and LDH release in isolated hearts. From these experiments an optimal concentration of KB-R7943 was identified and tested in pigs submitted to 48 min of coronary occlusion and 2 h of reperfusion. RESULTS: In myocytes, KB-R7943 at concentrations up to 15 microM reduced [Ca(2+)](i) rise and the probability of hypercontracture during re-energization (P<0.01). Nevertheless, in rat hearts, the effects of KB-R7943 applied during reperfusion after 60 min of ischemia depended on concentration and timing of administration. During the first 5 min of reperfusion, KB-R7943 (0.3-30 microM) induced a dose-dependent reduction in LDH release (half-response concentration 0.29 microM). Beyond 6 min of re-flow, KB-R7943 had no effect on LDH release, except at concentrations > or = 15 microM, which increased LDH. KB-R7943 at 5 microM given during the first 10 min of reflow reduced contractile dysfunction (P=0.011), LDH release (P=0.019) and contraction band necrosis (P=0.014) during reperfusion. Intracoronary administration of this concentration during the first 10 min of reperfusion reduced infarct size by 34% (P=0.033) in pigs submitted to 48 min of coronary occlusion. CONCLUSIONS: These results are consistent with the hypothesis that during initial reperfusion NCX activity results in net reverse mode operation contributing to Ca(2+) overload, hypercontracture and cell death, and that NCX inhibition during this phase is beneficial. Beyond this phase, NCX inhibition may impair forward mode-dependent Ca(2+) extrusion and be detrimental. These findings may help in the design of therapeutic strategies against lethal reperfusion injury, with NCX as the target.

Analysis of Variance↗

PubMed2002

Hypertrophic responsiveness of cardiomyocytes to alpha- or beta-adrenoceptor stimulation requires sodium-proton-exchanger-1 (NHE-1) activation but not cellular alkalization.

The influence of the sodium-proton-exchanger-1 (NHE-1) inhibitor HOE694 on alpha- or beta-adrenoceptor mediated stimulation of protein synthesis was investigated in cultured ventricular cardiomyocytes from adult rat pre-treated with fetal calf serum to induce hypertrophic responsiveness to beta-adrenoceptor stimulation. Stimulation of alpha-adrenoceptors with phenylephrine (10 microM) in bicarbonate-free medium caused cellular alkalization (Delta pH(i): + 0.17 +/- 0.02, n = 5, P < 0.05). HOE694, an NHE-1 inhibitor, completely abolished this effect. [14C]phenylalanine incorporation into cellular protein mass increased in the presence of phenylephrine by 23+/-8%, and this effect was also abolished in the presence of HOE694. HOE694 (1 mciroM) neither influenced basal protein synthesis nor interfered with alpha-adrenoceptor mediated activation of ERK2. Phorbol myristate acetate, a direct stimulator of protein kinase C, mimicked the effect of alpha-adrenoceptor stimulation in regard to protein synthesis, but did not lead to cellular alkalization. Protein synthesis increased in the presence of isoprenaline, a beta-adrenoceptor agonist also. Again, HOE694 attenuated the stimulation of protein synthesis although isoprenaline did not cause cellular alkalization. In conclusion, the growth response to different hypertrophic stimuli, namely alpha- or beta-adrenoceptor stimulation, is attenuated in the presence of the NHE-1 inhibitor HOE694 and this inhibition is independent from cellular alkalization.

Analysis of Variance↗