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Heimo Ehmke

Publications and source records attributed to Heimo Ehmke.

At least 19 recordsLinked to original sources
PubMed2006

NADPH oxidase accounts for enhanced superoxide production and impaired endothelium-dependent smooth muscle relaxation in BKbeta1-/- mice.

OBJECTIVE: Nitric oxide (NO)-induced vasorelaxation involves activation of large conductance Ca2+-activated K+ channels (BK). A regulatory BKbeta1 subunit confers Ca2+, voltage, and NO/cGMP sensitivity to the BK channel. We investigated whether endothelial function and NO/cGMP signaling is affected by a deletion of the beta1-subunit. METHODS AND RESULTS: Vascular superoxide in BKbeta1-/- was measured using the fluorescent dye hydroethidine and lucigenin-enhanced chemiluminescence. Vascular NO formation was analyzed using electron paramagnetic resonance (EPR), expression of NADPH oxidase subunits, the endothelial NO synthase (eNOS), the soluble guanylyl cyclase (sGC), as well as the activity and expression of the cyclic GMP-dependent kinase I (cGK-I) were assessed by Western blotting technique. eNOS, sGC, cGK-I expression and acetylcholine-induced NO production were unaltered in Bkbeta1-/- animals, whereas endothelial function was impaired and the activity of the cGK-I was reduced. Vascular O2- and expression of the NADPH oxidase subunits p67phox and Nox1 were increased. Endothelial dysfunction was normalized by the NADPH oxidase inhibitor apocynin. Potassium chloride- and iberiotoxin-induced depolarization mimicked the effect of BKbeta1-deletion by increasing vascular O2- in an NADPH-dependent fashion. CONCLUSIONS: The deletion of BKbeta1 causes endothelial dysfunction by increasing O2- formation via increasing activity and expression of the vascular NADPH oxidase.

Animals↗
PubMed2006

Engineered heart tissue grafts improve systolic and diastolic function in infarcted rat hearts.

The concept of regenerating diseased myocardium by implantation of tissue-engineered heart muscle is intriguing, but convincing evidence is lacking that heart tissues can be generated at a size and with contractile properties that would lend considerable support to failing hearts. Here we created large (thickness/diameter, 1-4 mm/15 mm), force-generating engineered heart tissue from neonatal rat heart cells. Engineered heart tissue formed thick cardiac muscle layers when implanted on myocardial infarcts in immune-suppressed rats. When evaluated 28 d later, engineered heart tissue showed undelayed electrical coupling to the native myocardium without evidence of arrhythmia induction. Moreover, engineered heart tissue prevented further dilation, induced systolic wall thickening of infarcted myocardial segments and improved fractional area shortening of infarcted hearts compared to controls (sham operation and noncontractile constructs). Thus, our study provides evidence that large contractile cardiac tissue grafts can be constructed in vitro, can survive after implantation and can support contractile function of infarcted hearts.

Animals↗
PubMed2006

Neurogenic mechanisms contribute to hypertension in mice with disruption of the K-Cl cotransporter KCC3.

The neurodegenerative disorder Andermann syndrome is caused by mutations of the K-Cl cotransporter KCC3. Mice with a targeted disruption of the corresponding gene, Slc12a6, reproduce neurodegeneration of the peripheral and central nervous system (CNS) and display arterial hypertension. Kcc3 is expressed in numerous tissues, including the CNS and vascular smooth muscle cells. As the intracellular chloride concentration may influence myogenic tone and hence blood pressure, we measured the chloride concentration in vascular smooth muscle cells. It was indeed increased in superficial brain arteries and saphenous arteries of Kcc3(-/-) mice. Isolated saphenous arteries and their third-order branches, however, reacted indistinguishably to changes in intravascular pressure, stimulation of alpha1-adrenoreceptors, exogenous nitric oxide, or blockade of calcium-activated chloride channels. Likewise, the responses to alpha1-adrenergic stimulation or exogenous nitric oxide in vivo were identical in both genotypes. These results argue against a major vascular-intrinsic component of arterial hypertension in Kcc3(-/-) mice. In contrast, either alpha1-adrenergic blockade or inhibition of ganglionic transmission abolished the difference in arterial blood pressure between both genotypes. This demonstrates a neurogenic component in the maintenance of this phenotype, which is further supported by an increase of urinary norepinephrine and epinephrine excretion in Kcc3(-/-) mice. Our data indicate that local control of myogenic tone does not require KCC3 and that hypertension in Kcc3(-/-) mice depends on an elevated sympathetic tone.

Aldosterone↗
PubMed2006

Impaired myocardial capillarogenesis and increased adaptive capillary growth in FGF2-deficient mice.

Basic fibroblast growth factor (FGF2) plays a major role in angiogenesis and capillary growth. In contrast to vascular endothelial growth factor, which is required for proliferation and survival of endothelial cells, FGF2 does not seem to be essential since the Fgf2 knockout is not lethal. Therefore, the precise genetic and physiological roles of FGF2 for capillary development and adaptation remain to be determined. Here we show that myocardial capillary supply is normal at birth, but significantly reduced by approximately 25% in adult Fgf2+/- and Fgf2-/- mice as compared with wild-type littermates. In contrast, after induction of myocardial hypertrophy by continuous infusion of angiotensin II (ANG II) for 6 days marked capillary growth was seen in both Fgf2+/- and Fgf2-/- mice, but not in wild-type littermates. These data demonstrate that two intact Fgf2 genes are necessary for normal capillary development after birth, whereas FGF2 seems to be dispensable for adaptive myocardial capillary growth in the adult mouse.

Angiotensin II↗
PubMed2005

Kv4.2 and KChIP2 transcription in individual cardiomyocytes from the rat left ventricular free wall.

Biophysical and genetic evidence suggests that Kv4-KChIP2 heteromeric ion channels are the molecular correlate of the dominating fast component of the cardiac transient outward K+ current (Itof). Since Itof is one of the essential currents contributing to the shape of the cardiac action potential in the rat, ferret, dog, and human heart, an important implication of this concept is that all ventricular cardiac myocytes from these species express members of the Kv4 and the KChIP2 gene family. To test this prediction, we developed a modified protocol for the collection and subsequent multiplex single-cell RT-PCR amplification of RNA from individual cardiomyocytes isolated from defined regions of the rat left ventricle. All cardiomyocytes investigated (n=61) were positive for alpha-MHC and Kv4.2 expression. KChIP2 mRNA could also be detected in the vast majority (approximately 87%) of cardiomyocytes. Nearly all of these myocytes co-expressed all three cardiac splice variants of KChIP2. In a small but distinct fraction of myocytes (13%), however, we failed to detect KChIP2 mRNA. The detection thresholds were similar for all target genes and approached a sensitivity of a few molecules of RNA per cell. Our findings support the hypothesis that Itof is mediated by Kv4-KChIP2 heteromeric ion channels in the great majority of cardiac myocytes. A small subpopulation of cardiomyocytes, however, appears to express KChIP2 mRNA at insignificant levels and may therefore use other accessory subunits to generate Itof.

Animals↗
PubMed2004

Ascending aortic stenosis selectively increases action potential-induced Ca2+ influx in epicardial myocytes of the rat left ventricle.

A decrease of the transient outward potassium current (Ito) has been observed in cardiac hypertrophy and contributes to the altered shape of the action potential (AP) of hypertrophied ventricular myocytes. Since the shape and duration of the ventricular AP are important determinants of the Ca2+ influx during the AP (QCa), we investigated the effect of ascending aortic stenosis (AS) on QCa in endo- and epicardial myocytes of the left ventricular free wall using the AP voltage-clamp technique. In sham-operated animals, QCa was significantly larger in endocardial compared to epicardial myocytes (803 +/- 65 fC pF(-1), n = 27 vs. 167 +/- 32 fC pF(-1), n = 38, P < 0.001). Ascending aortic stenosis significantly increased QCa in epicardial myocytes (368 +/- 54 fC pF(-1), n = 42, P < 0.05), but did not alter QCa in endocardial myocytes (696 +/- 65 fC pF(-1), n = 26). Peak and current-voltage relation of the AP-induced Ca2+ current were unaffected by AS. However, the time course of the current-voltage relation was significantly prolonged in epicardial myocytes of AS animals. Model calculations revealed that the increase in QCa can be ascribed to a prolonged opening of the activation gate, whereas an increase in inactivation prevents an excessive increase in QCa. In conclusion, AS significantly increased AP-induced Ca2+ influx in epicardial but not in endocardial myocytes of the rat left ventricle.

Action Potentials↗
PubMed2004

No aggravation of renal injury in apolipoprotein E knockout mice (ApoE(-/-)) after subtotal nephrectomy.

BACKGROUND: There is substantial experimental evidence that various forms of dyslipidaemia aggravate the course of renal failure and that reversal of dyslipidaemia ameliorates progression of renal failure. The apolipoprotein E knockout mouse (ApoE(-/-)) is an established model of accelerated atherogenesis. We investigated whether the course of renal disease after uninephrectomy (UNX) and subtotal nephrectomy (SNX) is altered in ApoE(-/-) mice compared with their genetic controls. METHODS: Ten-week-old, male ApoE(-/-) mice (body weight 25+/-2 g) were subjected either to sham operation (sham), UNX or SNX. C57BL/6 sham, UNX and SNX mice served as controls (body weight 26+/-3 g). The food intake of ApoE(-/-) and C57BL/6 mice was kept identical by a pair-feeding protocol. After 12 weeks, mean arterial blood pressure and heart rate were measured in awake resting mice, the kidneys were perfusion fixed and analysed using quantitative histological methods, immunohistochemistry and RT-PCR. RESULTS: At baseline, the sham ApoE(-/-) mice had significantly higher (P<0.05) serum cholesterol and triglycerides than the controls. In parallel, mean arterial blood pressure was significantly elevated in sham ApoE(-/-) mice compared with controls (137+/-15 vs 116+/-4 mmHg; P<0.05). In the sham groups, the glomerulosclerosis index was significantly higher in the ApoE(-/-) mice (1.05+/-0.14 vs 0.57+/-0.07; P<0.05), whereas the tubulointerstitial damage score was comparable (0.06+/-0.04 vs 0.04+/-0.02; n.s.). After SNX there was a significant increase in glomerulosclerosis index, but no difference could be detected between ApoE(-/-) and controls (1.75+/-0.16 vs 1.61+/-0.01, n.s.). The same was true for the tubulointerstitial damage index. CONCLUSIONS: Despite some glomerulosclerosis and elevated mean arterial blood pressure at baseline, no acceleration of progression of renal disease was found in this genetic model of hyperlipoproteinaemia. This observation suggests that despite the known spontaneous histological changes in untouched kidneys, however, the presence of hyperlipidaemia in the ApoE(-/-) mouse does not cause more severe progression in the present models of moderate renal disease.

Animals↗
PubMed2003

Extracellular Na+ removal attenuates rundown of the epithelial Na+-channel (ENaC) by reducing the rate of channel retrieval.

Regulation of the epithelial sodium channel (ENaC) is important for the long-term control of arterial blood pressure as evidenced by gain of function mutations of ENaC causing Liddle's syndrome, a rare form of hereditary arterial hypertension. In Xenopus laevis oocytes expressing ENaC a spontaneous decline of ENaC currents over time, so-called rundown, is commonly observed. Mechanisms involved in rundown may be physiologically relevant and may be related to feedback regulation of ENaC by intra- or extracellular Na+. We tested the effect of extracellular Na+ removal on ENaC rundown. Spontaneous rundown of ENaC was largely prevented by extracellular Na+ removal and was partially prevented by primaquine suggesting that it is due to endocytic channel retrieval. Liddle's syndrome mutation caused a reduced rate of rundown, and in oocytes expressing the mutated channel extracellular Na+ removal not only prevented rundown but even increased the ENaC currents (runup). Acute exposure to high extracellular Na+ drastically reduced whole-cell currents and surface expression of wild-type ENaC, while these effects were much smaller in ENaC with Liddle's syndrome mutation consistent with a stabilization of the mutated channel in the plasma membrane. Interestingly, the apparent intracellular Na+ concentration [Na+](i-app) was high (>60 mM) in ENaC-expressing oocytes but rundown was not associated with a further increase in [Na+](i-app). We conclude that the inhibitory effect of extracellular Na+ removal on rundown is due to an inhibition of endocytic ENaC retrieval.

Animals↗
PubMed2003

Loss of K-Cl co-transporter KCC3 causes deafness, neurodegeneration and reduced seizure threshold.

K-Cl co-transporters are encoded by four homologous genes and may have roles in transepithelial transport and in the regulation of cell volume and cytoplasmic chloride. KCC3, an isoform mutated in the human Anderman syndrome, is expressed in brain, epithelia and other tissues. To investigate the physiological functions of KCC3, we disrupted its gene in mice. This severely impaired cell volume regulation as assessed in renal tubules and neurons, and moderately raised intraneuronal Cl(-) concentration. Kcc3(-/-) mice showed severe motor abnormalities correlating with a progressive neurodegeneration in the peripheral and CNS. Although no spontaneous seizures were observed, Kcc3(-/-) mice displayed reduced seizure threshold and spike-wave complexes on electrocorticograms. These resembled EEG abnormalities in patients with Anderman syndrome. Kcc3(-/-) mice also displayed arterial hypertension and a slowly progressive deafness. KCC3 was expressed in many, but not all cells of the inner ear K(+) recycling pathway. These cells slowly degenerated, as did sensory hair cells. The present mouse model has revealed important cellular and systemic functions of KCC3 and is highly relevant for Anderman syndrome.

Animals↗
PubMed2003

Aquaporin-1 and HCO3(-)-Cl- transporter-mediated transport of CO2 across the human erythrocyte membrane.

Recent studies have suggested that aquaporin-1 (AQP1) as well as the HCO3(-)-Cl- transporter may be involved in CO2 transport across biological membranes, but the physiological importance of this route of gas transport remained unknown. We studied CO2 transport in human red blood cell ghosts at physiological temperatures (37 degrees C). Replacement of inert with CO2-containing gas above a stirred cell suspension caused an outside-to-inside directed CO2 gradient and generated a rapid biphasic intracellular acidification. The gradient of the acidifying gas was kept small to favour high affinity entry of CO2 passing the membrane. All rates of acidification except that of the approach to physicochemical equilibrium of the uncatalysed reaction were restricted to the intracellular environment. Inhibition of carbonic anhydrase (CA) demonstrated that CO2-induced acidification required the catalytic activity of CA. Blockade of the function of either AQP1 (by HgCl2 at 65 microM) or the HCO3(-)-Cl- transporter (by DIDS at 15 microM) completely prevented fast acidification. These data indicate that, at low chemical gradients for CO2, nearly the entire CO2 transport across the red cell membrane is mediated by AQP1 and the HCO3--Cl- transporter. Therefore, these proteins may function as high affinity sites for CO2 transport across the erythrocyte membrane.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2003

Myocyte loss in early left ventricular hypertrophy of experimental renovascular hypertension.

Left ventricular hypertrophy (LVH) develops very early in experimental renovascular hypertension after clipping of one renal artery and is accompanied by a remodeling of cardiac structure which has not yet been investigated in detail. It was the aim of the present study to analyze changes in cardiomyocyte number and volume in LVH after 2 weeks of renovascular hypertension. Sprague-Dawley rats were subjected to clipping of the left renal artery (2K1C) or sham operation (sham). One group of 2K1C rats received antihypertensive treatment with dihydralazine. The experiment was terminated after 2 weeks. Hearts were investigated using stereological methods, electron microscopy, immunohistology for the proliferation marker proliferating cell nuclear antigen, the pro- and anti-apoptotic proteins Bax and Bcl-2 as well as the TUNEL technique. After 2 weeks, systolic blood pressure and relative left ventricular weight were significantly higher in untreated 2K1C animals than in sham and dihydralazine-treated 2K1C rats. Volume fraction of interstitial tissue and capillary length density were not different, whereas wall thickness of intramyocardial arteries was significantly higher in untreated 2K1C (5.12+/-0.7 micro m) than in sham (3.92+/-0.6 micro m) and in dihydralazine-treated 2K1C (3.91+/-0.7 micro m) rats. Cardiomyocyte diameter and volume were significantly higher in untreated 2K1C than in sham animals. The number of cardiomyocytes per left ventricle was significantly lower in untreated 2K1C rats (5.5+/-1.6 vs 3.9+/-6.9 x10(7)). Using immunohistochemistry, no direct evidence of apoptosis was found, but a relative higher expression of the anti-apoptotic protein bcl-2 expression was seen in untreated 2K1C than in sham animals. This may reflect a protective mechanism as a consequence of earlier occurring apoptosis. These observations document that experimental renovascular hypertension induces a rapidly developing LVH characterized by marked cardiac remodeling and substantial loss of cadiomyocytes.

Animals↗
PubMed2003

A polycystin-2-like large conductance cation channel in rat left ventricular myocytes.

OBJECTIVE: Several members of the PKD gene family (PKD2, PKDL and PKD2L2) are expressed in the heart. Polycystin-2 and its homologues, which are encoded by these genes, have recently been shown to form Ca(2+)-regulated nonselective cation channels in heterologous expression systems. Previously, large conductance nonselective cation channels (LCC) have been described in cardiomyocytes, however, their molecular identity remained obscure. We therefore examined whether LCCs may be formed by polycystins. METHODS: Myocytes isolated from the rat left ventricle were investigated by the whole-cell patch-clamp technique and single-cell RT-PCR. RESULTS: Application of 10 mM caffeine to the bath solution to increase the intracellular Ca(2+) concentration led to activation of LCC in 56% of the myocytes investigated (total n=651), in approximately 10%, more than three LCCs were detected. The single channel conductance was approximately 300 pS for monovalent cations and the channel was relatively nonselective for the monovalent cations Na(+), K(+), Li(+), and Cs(+) and also permeable for the divalent cations Ca(2+) and Ba(2+), but impermeable for NMDG(+) and Cl(-). Amiloride (IC(50)=131+/-1.1 microM) and millimolar concentrations of the trivalent cations Gd(3+) and La(3+) inhibited the LCC. Single-cell RT-PCR analysis revealed that mRNA of PKD2 and PKD2L2, but not PKDL or PKD1 are expressed in individual rat left ventricular myocytes. CONCLUSION: The characteristics of LCC shown in the present study are nearly identical to those observed for polycystin-2 and its homologues suggesting that polycystin-2 or polycystin-2L2 underlie LCC in ventricular myocytes.

Amiloride↗
PubMed2003

Central sympathetic chemosensitivity and Kir1 potassium channels in the cat.

The possible involvement of potassium channels in central chemosensitivity, with special reference to the Kir1.1 potassium channel, was investigated by studying the CO(2) response of presympathetic neurons in the rostroventrolateral medulla (RVLM) in the absence or presence of various K(+) channel inhibitors. Synaptic input to RVLM neurons was blocked by local injection of omega-agatoxin and omega-conotoxin. Activity of RVLM neurons was measured by recording the electrical activity in preganglionic (WR-T(3)) or postganglionic (renal) sympathetic nerves after perfusion of the lower brainstem via the left vertebral artery with CO(2)-enriched saline solution. Unspecific K(+) channel blockade by BaCl(2) reduced the excitatory response of sympathetic activity after CO(2)-perfusion to 56% of control. A quantitatively similar inhibition of the central CO(2) response was obtained after administration of 9-fluorenylmethylchloroformate (FMOC-Cl) which eliminates pH sensitivity of Kir1 and Kir4.1. Furthermore, two structurally different Kir1 inhibiting toxins, tertiapin and Lq2, also reduced the central CO(2) response to approximately 50% of control. In contrast, charybdotoxin (CTX) had no effect on the CO(2) response. Using RT-PCR the expression of mRNA homologous to rat Kir1 mRNA was identified in the cat medulla oblongata. These data suggest that a modulation of potassium channel activity possibly via Kir1 may contribute to central chemosensitivity.

Animals↗
PubMed2003

The apolipoprotein e knockout mouse: a model documenting accelerated atherogenesis in uremia.

Rodents do not develop spontaneous atherosclerosis. Currently, there is no good animal model to study the effect of uremia on atherosclerosis. This study evaluated whether apolipoprotein E knockout (Apoe-/-) mice are useful to study the effect of renal dysfunction on cardiovascular risk. Apoe-/- mice have decreased serum apolipoprotein E and exhibit lipid abnormalities and atherosclerosis even on a low-cholesterol diet. Ten-wk-old Apoe-/- mice were subtotally nephrectomised (SNX Apoe-/-; n = 8), uninephrectomised (UNX Apoe-/-; n = 5), or sham-operated (sham Apoe-/-; n = 5) and compared with their genetic controls (SNX C57/BL6; UNX C57/BL6; sham C57/BL6). After 12 wk, BP was measured intraarterially, blood samples were taken, and the experiment was terminated by perfusion fixation. The heart weight was determined, and quantitative morphologic analysis of intramyocardial arteries and aortic changes was performed. At the end of the experiment, heart weight and relative left ventricular weight were comparable in all groups. Intraarterial BP was somewhat higher in Apoe-/- mice compared with controls. Baseline serum cholesterol and triglyceride levels were higher in Apoe-/- mice than in C57/BL6. Atherosclerotic plaques were not present in sham or UNX C57/BL6, but minor plaque formation was noted in some SNX control animals. In contrast, beginning plaques were seen even in untouched Apoe-/- mice, and strikingly increased plaque formation was noted in UNX and SNX Apoe-/- mice. Maximal plaque diameter (cross-section) was 37 +/- 74 micro m in SNX C57/BL6, 191 +/- 90 micro m in sham Apoe-/-, 323 +/- 66 micro m in UNX Apoe-/-, and 457 +/- 17 micro m in SNX Apoe-/-. The plaque morphology corresponded with that of early plaques characterized by foam cells and virtual absence of lymphocytes or smooth muscle cell infiltration. In conclusion, even mild renal dysfunction, i.e., after uninephrectomy, causes a dramatic increase in plaque size and aggressive morphology (foam cell rich soft plaques) in the animal model of the Apoe-/- mouse.

Animals↗