Biomedical subjects

Markus Rehm

Publications and source records attributed to Markus Rehm.

16 recordsLinked to original sources

PubMed2006

The endothelial glycocalyx affords compatibility of Starling's principle and high cardiac interstitial albumin levels.

OBJECTIVE: To test the role of an oncotic pressure gradient across the endothelial glycocalyx with respect to extravasation of fluid and colloids and development of tissue edema in a whole organ setting. METHODS: We measured filtration in the intact coronary system of isolated guinea pig hearts, comparing colloid-free perfusion and perfusion with 1.67% albumin or 2% hydroxyethylstarch (oncotic pressures 5.30 vs. 11.10 mm Hg, respectively). Heparinase was used to alter the endothelial glycocalyx. RESULTS: Extremely high net organ hydraulic conductivity was obtained with colloid-free perfusion (9.14 microl/min/g tissue). Supplementing perfusate with albumin caused a significant decrease, also vs. hydroxyethylstarch (1.04 vs. 2.67 microl/min/g, p < 0.05). Albumin also lowered edema formation vs. the other perfusion modes (p < 0.05). Stripping the glycocalyx of heparan sulfate reduced the effect of colloids, especially that of albumin. The steady-state concentrations of hydroxyethylstarch and albumin in the mixed interstitial fluid leaving the intact coronary bed averaged about 95% of the intravascular level. Electron and light microscopy indicated that colloid extravasated mainly in the venular sections. CONCLUSION: We propose a low-filtration model for the coronary system with different barrier properties in arteriolar/capillary and venular sections. Arteriolar/capillary: very little fluid and colloid extravasation due to the endothelial surface layer formed by the glycocalyx and albumin plus the endothelial strand barrier; venular: little net extravsation of fluid and colloids despite large pores, because of low hydrostatic and oncotic pressure differences between intra- and extravascular spaces. The latter sites provide physiological access of large solutes (colloids) to the tissue.

Albumins↗

PubMed2006

Technical and physiological background of plasma volume measurement with indocyanine green: a clarification of misunderstandings.

The indocyanine green (ICG) dilution technique (DT) is frequently used for plasma volume (PV) measurement. However, because of inadequate knowledge about the properties of this dye, lack of accuracy has been attributed to the method. The aim of this report is to provide physiological background information about the ICG-DT to avoid some profound misunderstandings. When performing tracer dilution, one has to consider the tracer's distribution space before interpreting the result. For ICG, the distribution space is the total PV, i.e., circulating + noncirculating PV, fixed within the endothelial glycocalyx. The distribution space of red blood cells and large molecules, in contrast, is only the circulating part of PV. Therefore, it is erroneous to compare directly PV derived from different tracer dilution methods. The transcapillary escape rate of ICG should not relevantly influence measured PV if the method is performed properly, i.e., if a short time window of measurement is subjected to monoexponential extrapolation. A major problem of PV measurement in general is that the target itself is very inconstant. Thus, checking for constancy of ICG-DT with two consecutive measurements is unreliable. Nevertheless, the ICG-DT is a useful tool for determining PV, provided it is well understood by the investigator to enable correct interpretation of the results.

Blood Volume Determination↗

PubMed2006

Systems analysis of effector caspase activation and its control by X-linked inhibitor of apoptosis protein.

Activation of effector caspases is a final step during apoptosis. Single-cell imaging studies have demonstrated that this process may occur as a rapid, all-or-none response, triggering a complete substrate cleavage within 15 min. Based on biochemical data from HeLa cells, we have developed a computational model of apoptosome-dependent caspase activation that was sufficient to remodel the rapid kinetics of effector caspase activation observed in vivo. Sensitivity analyses predicted a critical role for caspase-3-dependent feedback signalling and the X-linked-inhibitor-of-apoptosis-protein (XIAP), but a less prominent role for the XIAP antagonist Smac. Single-cell experiments employing a caspase fluorescence resonance energy transfer substrate verified these model predictions qualitatively and quantitatively. XIAP was predicted to control this all-or-none response, with concentrations as high as 0.15 microM enabling, but concentrations >0.30 microM significantly blocking substrate cleavage. Overexpression of XIAP within these threshold concentrations produced cells showing slow effector caspase activation and submaximal substrate cleavage. Our study supports the hypothesis that high levels of XIAP control caspase activation and substrate cleavage, and may promote apoptosis resistance and sublethal caspase activation in vivo.

Apoptosis↗

PubMed2006

Contrasting effects of colloid and crystalloid resuscitation fluids on cardiac vascular permeability.

BACKGROUND: Fluid extravasation may lead to myocardial edema and consequent reduction in ventricular function. Albumin is presumed to interact with the endothelial glycocalyx. The authors' objective was to compare the impact of different resuscitation fluids (human albumin, hydroxyethyl starch, saline) on vascular integrity. METHODS: In an isolated perfused heart model (guinea pig), Krebs-Henseleit buffer was augmented with colloids (one third volume 5% albumin or 6% hydroxyethyl starch 130/0.4) or crystalloid (0.9% saline). Perfusion pressure and vascular fluid filtration (epicardial transudate formation) were assessed at different flow rates. After global, stopped-flow ischemia (37 degrees C, 20 min), hearts were reperfused with the same resuscitation fluid additives. In a second series, the authors applied the respective perfusates after enzymatic digestion of the endothelial glycocalyx (heparinase, 10 U over 15 min). RESULTS: Both 5% albumin and 6% hydroxyethyl starch decreased fluid extravasation versus saline (68.4 +/- 5.9, 134.8 +/- 20.5, and 436.8 +/- 14.7 microl/min, respectively, at 60 cm H(2)O perfusion pressure; P < 0.05), the corresponding colloid osmotic pressures being 2.95, 5.45, and 0.00 mmHg. Digestion of the endothelial glycocalyx decreased coronary integrity in both colloid groups. After ischemia, a transient increase in vascular leak occurred with Krebs-Henseleit buffer containing hydroxyethyl starch and saline, but not with albumin. The authors observed no difference between intravascular and bulk interstitial colloid concentration in the steady state. Notwithstanding, electron microscopy revealed an intact endothelial glycocalyx and no interstitial edema in the albumin group. CONCLUSION: Ex vivo, albumin more effectively prevented fluid extravasation in the heart than crystalloid or artificial colloid. This effect was partly independent of colloid osmotic pressure and may be attributable to an interaction of albumin with the endothelial glycocalyx.

Albumins↗

PubMed2005

Real time single cell analysis of Bid cleavage and Bid translocation during caspase-dependent and neuronal caspase-independent apoptosis.

Bcl-2 homology domain (BH) 3-only proteins couple stress signals to evolutionarily conserved mitochondrial apoptotic pathways. Caspase 8-mediated cleavage of the BH3-only protein Bid into a truncated protein (tBid) and subsequent translocation of tBid to mitochondria has been implicated in death receptor signaling. We utilized a recombinant fluorescence resonance energy transfer (FRET) Bid probe to determine the kinetics of Bid cleavage and tBid translocation during death receptor-induced apoptosis in caspase 3-deficient MCF-7 cells. Cells treated with tumor necrosis factor-alpha (200 ng/ml) showed a rapid cleavage of the Bid-FRET probe occurring 75.4 +/- 12.6 min after onset of the tumor necrosis factor-alpha exposure. Cleavage of the Bid-FRET probe coincided with a translocation of tBid to the mitochondria and a collapse of the mitochondrial membrane potential (DeltaPsim). We next investigated the role of Bid cleavage in a model of caspase-independent, glutamate-induced excitotoxic apoptosis. Rat cerebellar granule neurons were transfected with the Bid-FRET probe and exposed to glutamate for 5 min. In contrast to death receptor-induced apoptosis, neurons showed a translocation of full-length Bid to the mitochondria. This translocation occurred 5.6 +/- 1.7 h after the termination of the glutamate exposure and was also paralleled with a collapse of the DeltaPsim. Proteolytic cleavage of the FRET probe also occurred, however, only 25.2 +/- 3.5 min after its translocation to the mitochondria. Subfractionation experiments confirmed a translocation of full-length Bid from the cytosolic to the mitochondrial fraction during excitotoxic apoptosis. Our data demonstrate that both tBid and full-length Bid have the capacity to translocate to mitochondria during apoptosis.

Animals↗

PubMed2005

Changes in acid-base balance following bolus infusion of 20% albumin solution in humans.

OBJECTIVE: To evaluate changes in acid-base balance following bolus infusions of a 20% albumin solution. DESIGN AND SETTING: Randomized prospective study in a university hospital. PATIENTS AND PARTICIPANTS: Two groups of eight patients each undergoing gynecological surgery. INTERVENTIONS: Patients were randomly assigned to receive either 0.9% saline or lactated Ringer's solution. At the end of surgery two boluses of 0.5 g/kg body weight of a 20% albumin solution were administered. Arterial blood gases, electrolytes, and total protein were measured. The strong ion difference and the amount of weak plasma acid were calculated. pH and titratable acidity of the 20% albumin solution were determined. MEASUREMENTS AND RESULTS: The infusion of a 20% albumin solution resulted in a significant decrease in pH from 7.284 to 7.262 in the saline group and from 7.422 to 7.394 in the Ringer's group. In both groups the 20% albumin solution caused an increase in strong ion difference and an increase in the amount of weak plasma acid. The observed changes in serum bicarbonate concentration were in good agreement with the changes in strong ion difference and the amount of weak plasma acid. The 20% albumin solution possessed a pH of 6.95 and a titratable acidity of 8.5 [corrected] mEq/l. CONCLUSIONS: According to the Stewart approach, the observed changes in acid-base balance are the net result of the two opposing effects of the strong ion difference and the amount of weak plasma acid. Alternatively, the acidifying effect of the 20% albumin solution may stem from the titratable acid content of the solution.

Acid-Base Equilibrium↗

PubMed2005

Atrial natriuretic peptide induces shedding of endothelial glycocalyx in coronary vascular bed of guinea pig hearts.

Atrial natriuretic peptide (ANP) is reported to enhance vascular permeability in vivo. Our aim was to evaluate the impact of ANP on coronary extravasation of fluids and macromolecules and on the integrity of the endothelial glycocalyx. Isolated guinea pig hearts (n = 6/group) were perfused with Krebs-Henseleit buffer in a Langendorff mode. A 6% hydroxyethyl starch (HES) solution was infused into the coronary system for 20 min without (Control group) and simultaneously with (ANP group) ANP at 10(-9) M. In two further series, the glycocalyx was enzymatically degraded by means of heparinase (Hep) application (10 IU over 15 min), followed again by the infusion of HES in the absence (Hep group) and presence (ANP+Hep group) of ANP. Net fluid filtration, extravasation of HES, electron microscopic visualization of the glycocalyx, and quantification of shedding of syndecan-1, a component of the glycocalyx, were determined. An increase in fluid leak was observed in ANP, ANP+Hep, and Hep hearts [+29%, +31%, +14%, respectively; a decrease was observed in Control hearts (-13%)]. Similarly, an accelerated extravasation of colloid was observed in these three groups. Coronary release of syndecan-1 increased 9- to 18-fold during infusion of ANP. Electron microscopy revealed a dramatic degradation of the glycocalyx after ANP. These results indicate that the endothelial glycocalyx serves as a barrier to transmural exchange of fluid and colloid in the coronary vascular system. ANP causes rapid shedding of individual components of the glycocalyx and histologically detectable degradation. Thus the permeability-increasing effect of ANP may be at least partially related to changes in the integrity of the endothelial glycocalyx.

Animals↗

PubMed2005

Effect of hypertonic saline dextran on acid-base balance in patients undergoing surgery of abdominal aortic aneurysm.

OBJECTIVE: To evaluate the magnitude and cause of metabolic acidosis after infusion of 7.5% sodium chloride 6% dextran 70. DESIGN: Randomized, prospective clinical study. SETTING: University hospital. PATIENTS: Two groups of 14 patients each, undergoing repair of abdominal aortic aneurysm. INTERVENTIONS: Patients were randomly assigned to receive either 250 mL of hypertonic saline dextran (HSD) or a conventional fluid regimen with 250 mL of hydroxyethyl starch in normal saline solution (H-NS) during the period of aortic clamping. Additionally, normal saline was used in both groups to reach a target pulmonary artery occlusion pressure of 15-18 mmHg. pH, Paco2, and serum concentrations of sodium, potassium, magnesium, calcium, chloride, lactate, albumin, and phosphate were measured. Strong ion difference was calculated as (sodium + potassium + magnesium + calcium) - (chloride + lactate). The amount of weak plasma acid was calculated. MEASUREMENTS AND MAIN RESULTS: The infusion of HSD resulted in an immediate large increase in serum sodium (19 mmol/L) and chloride (22 mmol/L), whereas the infusion of H-NS led only to mild increases in serum sodium (3 mmol/L) and chloride (6 mmol/L). Both HSD and H-NS caused concomitant and equal decreases in the amount of weak plasma acid, strong ion difference, and pH (7.28-7.30). The reduction of bicarbonate was also identical and proportional to the extent of dilution due to infusion of HSD and H-NS. This induced metabolic acidosis was corrected spontaneously in both groups 24 hrs after surgery. CONCLUSION: Both the intravenous administration of 7.5% sodium chloride and the conventional fluid regimen with saline-based 6% hydroxyethyl starch solution resulted in a metabolic acidosis of equal extent. This suggests dilution of plasma buffers or a decrease in strong ion difference to be the primary cause of metabolic acidosis.

Acid-Base Equilibrium↗

PubMed2005

Development and validation of a mathematical algorithm for quantifying preoperative blood volume by means of the decrease in hematocrit resulting from acute normovolemic hemodilution.

BACKGROUND: The interindividual variability of blood volume (BV) is high. The aim of this work was to use the decrease in large-vessel hematocrit (HK(LV)) during acute normovolemic hemodilution (ANH) as an instrument for estimating preoperative BV. STUDY DESIGN AND METHODS: In 39 patients, (Group 1) preoperative ANH was performed. Plasma volume, red cell volume, and HK(LV) were measured before and 30 minutes after ANH, respectively. In a retrospective analysis, a mathematical algorithm was developed for estimating BV before ANH by means of the measured changes in HK(LV) and the amount of blood removed during ANH. To validate the method prospectively, ANH was performed in an additional 10 patients (Group 2). Preoperative BV was estimated and measured in the same way as in Group 1. RESULTS: In Group 1, the mean difference between estimated and measured BV before ANH was 200 +/- 403 mL (5.14 +/- 10.12%; p > 0.05; r = 0.8). In Group 2, the estimated BV before ANH was 41 +/- 348 mL (-0.53 +/- 7.84%) lower than the measured BV (p > 0.05; r = 0.94). In this group, however, two patients with an extraordinarily small (2691 mL) and large (6172 mL) preoperative BV, respectively, were identified correctly by means of the algorithm. CONCLUSIONS: The changes in HK(LV) determined during ANH provide a good "bedside" estimation of preoperative BV.

Algorithms↗

PubMed2004

Endothelial glycocalyx as an additional barrier determining extravasation of 6% hydroxyethyl starch or 5% albumin solutions in the coronary vascular bed.

BACKGROUND: The impact on the endothelial glycocalyx for the extravasation of colloidal infusion solutions has not been investigated sufficiently. METHODS: Isolated guinea pig hearts were perfused with Krebs-Henseleit buffer in a Langendorff mode. Solutions of 0.9% saline, 5% albumin (70 kd), or 6% hydroxyethyl starch (200 kd) were infused into the coronary system for 20 min at a rate of one third of the coronary flow, also during reperfusion after 15 min of ischemia, and after enzymatic digestion of the endothelial glycocalyx by heparinase. Net coronary fluid filtration was assessed directly by measuring the formation of transudate on the epicardial surface, and solute extravasation was assessed by measuring albumin and hydroxyethyl starch in the coronary effluent and transudate. Hearts were perfusion fixed to visualize the endothelial glycocalyx using transmission electron microscopy. RESULTS: Only infusion of hydroxyethyl starch, not infusion of albumin, significantly decreased net coronary fluid filtration. Heparinase application without ischemia increased coronary leak by 25% but did not accelerate the passage of colloids. Ischemia alone did not alter permeability. However, there was a large (approximately +200%), transient (approximately 4 min) increase in permeability for water, albumin, and hydroxyethyl starch after ischemia with heparinase application. Also, histamine (10 m) only increased permeability after pretreatment of the hearts with heparinase. The thickness of the glycocalyx after colloid administration was 0.2-0.3 microm. No glycocalyx could be detected after application of heparinase. CONCLUSION: The endothelial glycocalyx acts as a competent barrier for water and colloids. Only after its destruction do changes in endothelial morphology (postischemic reperfusion or histamine application) become effective determinants of coronary extravasation.

Animals↗

PubMed2004

Severe metabolic acidosis resulting from a dislocated gastric band.

A 32-year-old morbidly obese woman with an obstructing dislocated gastric band is presented. Because of prolonged vomiting, a metabolic alkalosis would be expected, but instead an impressive high anion gap acidosis was observed. Because of a highly positive urine ketone test and a high serum concentration of beta-hydroxybutyrate, a ketoacidosis caused by starvation appears to be the primary cause of this metabolic acidosis. This type of acidosis was treated successfully with intravenous administration of glucose and insulin as well as sodium bicarbonate, with urgent removal of the band.

Acidosis↗

PubMed2003

Real-time single cell analysis of Smac/DIABLO release during apoptosis.

We examined the temporal and causal relationship between Smac/DIABLO release, cytochrome c (cyt-c) release, and caspase activation at the single cell level during apoptosis. Cells treated with the broad-spectrum caspase inhibitor z-VAD-fmk, caspase-3 (Casp-3)-deficient MCF-7 cells, as well as Bax-deficient DU-145 cells released Smac/DIABLO and cyt-c in response to proapoptotic agents. Real-time confocal imaging of MCF-7 cells stably expressing Smac/DIABLO-yellow fluorescent protein (YFP) revealed that the average duration of Smac/DIABLO-YFP release was greater than that of cyt-c-green fluorescent protein (GFP). However, there was no significant difference in the time to the onset of release, and both cyt-c-GFP and Smac/DIABLO-YFP release coincided with mitochondrial membrane potential depolarization. We also observed no significant differences in the Smac/DIABLO-YFP release kinetics when z-VAD-fmk-sensitive caspases were inhibited or Casp-3 was reintroduced. Simultaneous measurement of DEVDase activation and Smac/DIABLO-YFP release demonstrated that DEVDase activation occurred within 10 min of release, even in the absence of Casp-3.

Apoptosis↗

PubMed2003

Outer mitochondrial membrane permeabilization during apoptosis triggers caspase-independent mitochondrial and caspase-dependent plasma membrane potential depolarization: a single-cell analysis.

Little is known about the temporal relationship between mitochondrial and plasma membrane potential changes and outer mitochondrial membrane permeabilization during apoptosis. Confocal imaging of breast carcinoma and HeLa cells stably transfected with cytochrome-C-GFP demonstrated that mitochondria rapidly depolarized after the release of the fusion protein into the cytosol. Of note, mitochondria did not completely depolarize but established a new steady-state level that could be further dissipated by treatment with the protonophore carbonyl cyanide p-trifluoromethoxy-phenylhydrazone. Treatment with the F(O)F(1)-ATP-synthase inhibitor oligomycin likewise induced a collapse of this steady-state level, suggesting that F(O)F(1)-ATP-synthase reversal maintained mitochondrial potential after outer mitochondrial membrane permeabilization. Treatment with a broad spectrum caspase inhibitor failed to inhibit the partial depolarization of mitochondria during apoptosis, yet potently abolished the activation of effector caspases detected by fluorescence resonance energy transfer analysis in the same experiment. Interestingly, the onset of mitochondrial depolarization was always coupled with a depolarization of the plasma membrane potential. This was associated with the degradation of the regulatory Na(+)/K(+)-ATPase beta-subunit, and both events were blocked by caspase inhibition. Our results demonstrate that outer mitochondrial membrane permeabilization coordinates the depolarization of both membrane potentials during apoptosis.

Apoptosis↗

PubMed2003

Mitochondrial membrane permeabilization and superoxide production during apoptosis. A single-cell analysis.

The temporal relationship between mitochondrial membrane permeabilization and reactive oxygen species production during apoptosis remains unknown. We analyzed the rate of superoxide production of human breast carcinoma cells expressing a cytochrome c-green fluorescent protein (cyt-c-GFP) fusion protein at the single-cell level during apoptosis. In cells treated with the proapoptotic agents staurosporine (3 microm) or tumor necrosis factor-alpha (100 ng/ml), the release of cyt-c-GFP was individually set for each cell, and the majority of the fusion protein was released in less than 10 min. Prior to the release of the fusion protein, cells demonstrated a constant rate of superoxide production determined with the probe hydroethidine. After the release was completed, the superoxide concentration increased rapidly to a level more than 3-fold above baseline. Treatment with the broad spectrum caspase inhibitor z-Val-Ala-Asp(O-methyl)-fluoromethylketone (z-VAD-fmk; 200 microm) did not alter the kinetics of the cyt-c-GFP release but significantly reduced superoxide concentration after the release of cyt-c-GFP. Interestingly, treatment with z-VAD-fmk also reduced the increase in superoxide concentration in response to menadione in the absence of mitochondrial cyt-c-GFP release. Mitochondrial depolarization with the protonophore carbonyl cyanide p-trifluoromethoxy-phenylhydrazone per se did not trigger cyt-c-GFP release or an increase in superoxide production. Our data suggest that mitochondria increase their superoxide production during apoptosis directly after the quantitative release of soluble intermembrane proteins and demonstrate novel antioxidative effects of the commonly used caspase inhibitor z-VAD-fmk.

Apoptosis↗

PubMed2003

Treating intraoperative hyperchloremic acidosis with sodium bicarbonate or tris-hydroxymethyl aminomethane: a randomized prospective study.

UNLABELLED: In this study, we evaluated the action of two buffer solutions on acid-base equilibrium in cases of hyperchloremic acidosis. Twenty-four patients undergoing major gynecological intraabdominal surgery received 40 mL. kg(-1). h(-1) of 0.9% saline per protocol. During surgery, in every patient, hyperchloremic acidosis occurred. At a standard base excess of -7 mmol/L, the patients were randomly assigned to receive within 20 min either a mean of 130 +/- 26 mmol of sodium bicarbonate (BIC, 1 M; n = 12) or a mean of 128 +/- 18 mmol of tris-hydroxymethyl aminomethane (THAM, 3 M; n = 12). PaCO(2), pH, serum bicarbonate concentration, standard base excess, and serum concentrations of sodium, potassium, chloride, lactate, phosphate, total protein, and albumin were determined before and 0, 10, and 20 min after buffering. The apparent strong ion difference was calculated as: serum sodium plus serum potassium minus serum chloride minus serum lactate. The effective strong ion difference and the amount of weak plasma acid were calculated by using a computer program. Immediately after buffering, standard base excess increased by 9.8 mmol/L in the BIC group and by 7.2 mmol/L in the THAM group. In both groups, PaCO(2) and the amount of weak plasma acid remained constant. Mainly because of hypernatremia, the apparent and effective strong ion difference increased in the BIC group by 8.5 and 7.9 mEq/L, respectively. In the THAM group, the apparent strong ion difference remained constant; however, the effective strong ion difference increased by 6.4 mEq/L and the anion gap decreased by 5.8 mmol/L because of the occurrence of an unmeasured cation. In conclusion, in case of buffering with BIC or THAM, the changes in pH were accompanied by, and probably caused by, an increase in strong ion difference. IMPLICATIONS: By comparing two groups of patients with intraoperative hyperchloremic acidosis receiving equal doses of either sodium bicarbonate or tris-hydroxymethyl aminomethane, we assessed the action of both drugs on acid-base equilibrium. In case of "buffering," the changes in pH were accompanied by, and probably caused by, an increase in strong ion difference.

Acid-Base Equilibrium↗

PubMed2002

Single-cell fluorescence resonance energy transfer analysis demonstrates that caspase activation during apoptosis is a rapid process. Role of caspase-3.

Activation of effector caspases is considered to be the final step in many apoptosis pathways. We transfected HeLa cells with a recombinant caspase substrate composed of cyan and yellow fluorescent protein and a linker peptide containing the caspase cleavage sequence DEVD, and we examined the cleavage kinetics at the single-cell level by fluorescence resonance energy transfer (FRET) analysis. Caspase activation in response to tumor necrosis factor-alpha, staurosporine, or etoposide resulted in cleavage of the linker peptide and subsequent disruption of the FRET signal. The time to caspase activation varied among individual cells, depending on the type of treatment and concentration used. However, once initiated, disruption of the FRET signal was always rapid (<or=15 min) and largely independent of these parameters. In contrast, FRET probe cleavage was significantly slower in the caspase-3-deficient MCF-7 cells, particularly at low concentrations of the pro-apoptotic agents. Under these conditions, MCF-7 cells required up to 90 min for the FRET probe cleavage, whereas MCF-7/Casp-3 cells displayed rapid cleavage kinetics. Interestingly, we could still observe comparable cell death rates in MCF-7 and MCF-7/Casp-3 cells. Our results suggest that caspase activation during apoptosis occurs in an "all or nothing" fashion. Caspase-3 is required for rapid cleavage kinetics when the onset of apoptosis is slow, suggesting the existence of caspase-3-dependent feedback loops.

Apoptosis↗