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Rudolf Schubert

Publications and source records attributed to Rudolf Schubert.

10 recordsLinked to original sources
PubMed2006

Impaired endothelium-derived hyperpolarizing factor-mediated dilations and increased blood pressure in mice deficient of the intermediate-conductance Ca2+-activated K+ channel.

The endothelium plays a key role in the control of vascular tone and alteration in endothelial cell function contributes to several cardiovascular disease states. Endothelium-dependent dilation is mediated by NO, prostacyclin, and an endothelium-derived hyperpolarizing factor (EDHF). EDHF signaling is thought to be initiated by activation of endothelial Ca(2+)-activated K(+) channels (K(Ca)), leading to hyperpolarization of the endothelium and subsequently to hyperpolarization and relaxation of vascular smooth muscle. In the present study, we tested the functional role of the endothelial intermediate-conductance K(Ca) (IK(Ca)/K(Ca)3.1) in endothelial hyperpolarization, in EDHF-mediated dilation, and in the control of arterial pressure by targeted deletion of K(Ca)3.1. K(Ca)3.1-deficient mice (K(Ca)3.1(-/-)) were generated by conventional gene-targeting strategies. Endothelial K(Ca) currents and EDHF-mediated dilations were characterized by patch-clamp analysis, myography and intravital microscopy. Disruption of the K(Ca)3.1 gene abolished endothelial K(Ca)3.1 currents and significantly diminished overall current through K(Ca) channels. As a consequence, endothelial and smooth muscle hyperpolarization in response to acetylcholine was reduced in K(Ca)3.1(-/-) mice. Acetylcholine-induced dilations were impaired in the carotid artery and in resistance vessels because of a substantial reduction of EDHF-mediated dilation in K(Ca)3.1(-/-) mice. Moreover, the loss of K(Ca)3.1 led to a significant increase in arterial blood pressure and to mild left ventricular hypertrophy. These results indicate that the endothelial K(Ca)3.1 is a fundamental determinant of endothelial hyperpolarization and EDHF signaling and, thereby, a crucial determinant in the control of vascular tone and overall circulatory regulation.

Acetylcholine↗
PubMed2006

Evidence for a functional role of endothelial transient receptor potential V4 in shear stress-induced vasodilatation.

OBJECTIVE: Ca2+-influx through transient receptor potential (TRP) channels was proposed to be important in endothelial function, although the precise role of specific TRP channels is unknown. Here, we investigated the role of the putatively mechanosensitive TRPV4 channel in the mechanisms of endothelium-dependent vasodilatation. METHODS AND RESULTS: Expression and function of TRPV4 was investigated in rat carotid artery endothelial cells (RCAECs) by using in situ patch-clamp techniques, single-cell RT-PCR, Ca2+ measurements, and pressure myography in carotid artery (CA) and Arteria gracilis. In RCAECs in situ, TRPV4 currents were activated by the selective TRPV4 opener 4alpha-phorbol-12,13-didecanoate (4alphaPDD), arachidonic acid, moderate warmth, and mechanically by hypotonic cell swelling. Single-cell RT-PCR in endothelial cells demonstrated mRNA expression of TRPV4. In FURA-2 Ca2+ measurements, 4alphaPDD increased [Ca2+]i by &140 nmol/L above basal levels. In pressure myograph experiments in CAs and A gracilis, 4alphaPDD caused robust endothelium-dependent and strictly endothelium-dependent vasodilatations by &80% (K(D) 0.3 microL), which were suppressed by the TRPV4 blocker ruthenium red (RuR). Shear stress-induced vasodilatation was similarly blocked by RuR and also by the phospholipase A2 inhibitor arachidonyl trifluoromethyl ketone (AACOCF3). 4alphaPDD produced endothelium-derived hyperpolarizing factor (EDHF)-type responses in A gracilis but not in rat carotid artery. Shear stress did not produce EDHF-type vasodilatation in either vessel type. CONCLUSIONS: Ca2+ entry through endothelial TRPV4 channels triggers NO- and EDHF-dependent vasodilatation. Moreover, TRPV4 appears to be mechanistically important in endothelial mechanosensing of shear stress.

Animals↗
PubMed2006

Urocortin-induced decrease in Ca2+ sensitivity of contraction in mouse tail arteries is attributable to cAMP-dependent dephosphorylation of MYPT1 and activation of myosin light chain phosphatase.

Urocortin, a vasodilatory peptide related to corticotropin-releasing factor, may be an endogenous regulator of blood pressure. In vitro, rat tail arteries are relaxed by urocortin by a cAMP-mediated decrease in myofilament Ca2+ sensitivity through a still unclear mechanism. Here we show that contraction of intact mouse tail arteries induced with 42 mmol/L KCl or 0.5 micromol/L noradrenaline was associated with a approximately 2-fold increase in the phosphorylation of the regulatory subunit of myosin phosphatase (SMPP-1M), MYPT1, at Thr696, which was reversed in arteries relaxed with urocortin. Submaximally (pCa 6.1) contracted mouse tail arteries permeabilized with alpha-toxin were relaxed with urocortin by 39+/-3% at constant [Ca2+], which was associated with a decrease in myosin light chain (MLC20Ser19), MYPT1Thr696, and MYPT1Thr850 phosphorylation by 60%, 28%, and 52%, respectively. The Rho-associated kinase (ROK) inhibitor Y-27632 decreased MYPT1 phosphorylation by a similar extent. Inhibition of PP-2A with 3 nmol/L okadaic acid had no effect on MYPT1 phosphorylation, whereas inhibition of PP-1 with 3 micromol/L okadaic acid prevented dephosphorylation. Urocortin increased the rate of dephosphorylation of MLC20Ser19 approximately 2.2-fold but had no effect on the rate of contraction under conditions of, respectively, inhibited kinase and phosphatase activities. The effect of urocortin on MLC20Ser19 and MYPT1 phosphorylation was blocked by Rp-8-CPT-cAMPS and mimicked by Sp-5,6-DCl-cBIMPS. In summary, these results provide evidence that Ca(2+)-independent relaxation by urocortin can be attributed to a cAMP-mediated increased activity of SMPP-1M which at least in part is attributable to a decrease in the inhibitory phosphorylation of MYPT1.

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↗
PubMed2005

Elevated blood pressure linked to primary hyperaldosteronism and impaired vasodilation in BK channel-deficient mice.

BACKGROUND: Abnormally elevated blood pressure is the most prevalent risk factor for cardiovascular disease. The large-conductance, voltage- and Ca2+-dependent K+ (BK) channel has been proposed as an important effector in the control of vascular tone by linking membrane depolarization and local increases in cytosolic Ca2+ to hyperpolarizing K+ outward currents. However, the BK channel may also affect blood pressure by regulating salt and fluid homeostasis, particularly by adjusting the renin-angiotensin-aldosterone system. METHODS AND RESULTS: Here we report that deletion of the pore-forming BK channel alpha subunit leads to a significant blood pressure elevation resulting from hyperaldosteronism accompanied by decreased serum K+ levels as well as increased vascular tone in small arteries. In smooth muscle from small arteries, deletion of the BK channel leads to a depolarized membrane potential, a complete lack of membrane hyperpolarizing spontaneous K+ outward currents, and an attenuated cGMP vasorelaxation associated with a reduced suppression of Ca2+ transients by cGMP. The high level of BK channel expression observed in wild-type adrenal glomerulosa cells, together with unaltered serum renin activities and corticotropin levels in mutant mice, suggests that the hyperaldosteronism results from abnormal adrenal cortical function in BK(-/-) mice. CONCLUSIONS: These results identify previously unknown roles of BK channels in blood pressure regulation and raise the possibility that BK channel dysfunction may underlie specific forms of hyperaldosteronism.

Adrenal Cortex↗
PubMed2005

Modulation of the myogenic response by neurogenic influences in rat small arteries.

The hypothesis that the amplitude of the myogenic response is modulated by factors released from nerve endings was tested in rat tail small arteries. A pressure myograph in conjunction with direct stimulation of nerve endings by electrical field stimulation (EFS) was used to determine rat small artery contractile reactions. Vessel pretreatment with 10(- 5) M phentolamine abolished EFS-induced reactions completely indicating that they are mediated mainly by an adrenoceptor agonist, probably noradrenaline. In the absence and presence of 10(- 5) M phentolamine, vessel diameter changes in the pressure range from 10 to 120 mmHg were not different. Vessel stimulation by (i) EFS, (ii) noradrenaline, (iii) selective stimulation of alpha1- and alpha2-receptors, (iv) serotonin, or (v) vasopressin significantly reduced the diameter change induced by stepping pressure from 10 to 40 mmHg compared to unstimulated, control vessels. Vessel diameter changes induced by stepping pressure from 40 to 80 and from 80 to 120 mmHg, however, were not different in vessels stimulated with EFS and noradrenaline compared to controls. In conclusion, these data show that factors released from unstimulated adrenergic nerve endings (i.e., not stimulated by EFS) are not involved in the myogenic response. In contrast, factors released upon stimulation of nerve endings can modulate the amplitude of the myogenic response, but only at low pressures. Thus, the pressure range for myogenic blood flow autoregulation is extended to lower pressures. Myogenic autoregulation of blood flow at physiological pressures is unaltered.

Adrenergic alpha-Antagonists↗
PubMed2004

Nitric oxide donor sodium nitroprusside dilates rat small arteries by activation of inward rectifier potassium channels.

The role of vascular smooth muscle inward rectifier K+ (K(IR)) channels in the mechanisms underlying vasodilation is still unclear. The hypothesis that K(IR) channels are involved in sodium nitroprusside (SNP)-induced dilation of rat-tail small arteries was tested. SNP relaxed tail small arteries with an EC50 of 2.6x10(-8) mol/L. Endothelium removal did not attenuate this effect. Vessel pretreatment with hydroxocobalamin, a nitric oxide (NO) scavenger, but not with rhodanese and sodium thiosulfate, inactivators of cyanide (CN), abolished the SNP effect. Vessel pretreatment with 10(-5) mol/L Ba2+, a specific blocker of K(IR) channels at micromolar concentrations, reduced the SNP effect. Low concentrations of K+ dilated the vessels; this effect was attenuated largely after pretreatment with 3x10(-5) mol/L Ba2+. In freshly isolated smooth muscle cells, a barium-sensitive current was observed at potentials negative to the potassium equilibrium potential. Application of 10(-4) mol/L SNP increased the barium-sensitive current 1.79+/-0.23-fold at -100 mV and hyperpolarized the membrane potential by 8.6+/-0.5 mV. In tissue from freshly dissected vessels, transcripts for K(IR) 2.1 and 2.2, but not for K(IR) 2.3 and 2.4, were found. However, only K(IR) 2.1 antibodies immunostained the tunica media of the vessel. These data suggest that vascular smooth muscle K(IR) 2.1 channels are involved in the SNP-induced dilation of rat-tail small arteries.

Animals↗
PubMed2002

Rho kinase inhibition partly weakens myogenic reactivity in rat small arteries by changing calcium sensitivity.

The hypothesis that Rho kinase is involved in myogenic reactivity was investigated in pressurized rat tail small arteries using videomicroscopic diameter determination and calcium fluorimetry. The potent Rho kinase inhibitor Y-27632 reversibly increased vessel diameter at 80 mmHg without changing the intracellular calcium concentration ([Ca](i)) shifting the relationship between diameter change and [Ca](i) to higher calcium levels. Neither endothelium removal nor inhibition of neural transmission affected the Y-27632-induced effect. Y-27632 at 3 x 10(-6) mol/l attenuated the myogenic response in the pressure range from 10 to 120 mmHg, shifting the relationship between vessel tone and [Ca](i) to higher calcium levels. In addition, the Y-27632-induced shift of the relationship between vessel tone and [Ca](i) was larger at 80 than at 10 mmHg. These results suggest that smooth muscle cell Rho kinase in rat tail small arteries 1) is in an active state partly determining the level of the myogenic tone, and 2) alters the strength of the myogenic response by changing calcium sensitivity, probably caused by the pressure-induced activation of the kinase.

Amides↗