The kidney plays a key role in the correction of systemic acid-base imbalances. Central for this regulation are the intercalated cells in the distal nephron, which secrete acid or base into the ...urine. How these cells sense acid-base disturbances is a long-standing question. Intercalated cells exclusively express the Na
-dependent Cl
/HCO
exchanger AE4 (Slc4a9). Here we show that AE4-deficient mice exhibit a major dysregulation of acid-base balance. By combining molecular, imaging, biochemical and integrative approaches, we demonstrate that AE4-deficient mice are unable to sense and appropriately correct metabolic alkalosis and acidosis. Mechanistically, a lack of adaptive base secretion via the Cl
/HCO
exchanger pendrin (Slc26a4) is the key cellular cause of this derailment. Our findings identify AE4 as an essential part of the renal sensing mechanism for changes in acid-base status.
Large-conductance potassium (BK) channels in vascular smooth muscle cells (VSMCs) sense both changes in membrane potential and in intracellular Ca(2+) concentration. BK channels may serve as negative ...feedback regulators of vascular tone by linking membrane depolarization and local increases in intracellular Ca(2+) concentration (Ca(2+) sparks) to repolarizing spontaneous transient outward K(+) currents (STOCs). BK channels are composed of channel-forming BKalpha and auxiliary BKbeta1 subunits, which confer to BK channels an increased sensitivity for changes in membrane potential and Ca(2+). To assess the in vivo functions of this ss subunit, mice with a disrupted BKbeta1 gene were generated. Cerebral artery VSMCs from BKbeta1 -/- mice generated Ca(2+) sparks of normal amplitude and frequency, but STOC frequencies were largely reduced at physiological membrane potentials. Our results indicate that BKbeta1 -/- mice have an abnormal Ca(2+) spark/STOC coupling that is shifted to more depolarized potentials. Thoracic aortic rings from BKbeta1 -/- mice responded to agonist and elevated KCl with a increased contractility. BKbeta1 -/- mice had higher systemic blood pressure than BKbeta1 +/+ mice but responded normally to alpha(1)-adrenergic vasoconstriction and nitric oxide-mediated vasodilation. We propose that the elevated blood pressure in BKbeta1 -/- mice serves to normalize Ca(2+) spark/STOC coupling for regulating myogenic tone. The full text of this article is available at http://www.circresaha.org.
Cardiac atrophy as a consequence of mechanical unloading develops following exposure to microgravity or prolonged bed rest. It also plays a central role in the reverse remodelling induced by left ...ventricular unloading in patients with heart failure. Surprisingly, the intracellular Ca
2+
transients which are pivotal to electromechanical coupling and to cardiac plasticity were repeatedly found to remain unaffected in early cardiac atrophy. To elucidate the mechanisms underlying the preservation of the Ca
2+
transients, we investigated Ca
2+
cycling in cardiomyocytes from mechanically unloaded (heterotopic abdominal heart transplantation) and control (orthotopic) hearts in syngeneic Lewis rats. Following 2 weeks of unloading, sarcoplasmic reticulum (SR) Ca
2+
content was reduced by ~55 %. Atrophic cardiac myocytes also showed a much lower frequency of spontaneous diastolic Ca
2+
sparks and a diminished systolic Ca
2+
release, even though the expression of ryanodine receptors was increased by ~30 %. In contrast, current clamp recordings revealed prolonged action potentials in endocardial as well as epicardial myocytes which were associated with a two to fourfold higher sarcolemmal Ca
2+
influx under action potential clamp. In addition, Cav1.2 subunits which form the pore of L-type Ca
2+
channels (LTCC) were upregulated in atrophic myocardium. These data suggest that in early cardiac atrophy induced by mechanical unloading, an augmented sarcolemmal Ca
2+
influx through LTCC fully compensates for a reduced systolic SR Ca
2+
release to preserve the Ca
2+
transient. This interplay involves an electrophysiological remodelling as well as changes in the expression of cardiac ion channels.
Background and purpose:
Rho‐kinase (ROCK) has been implicated in the pathophysiology of altered vasoregulation leading to hypertension. Here we describe the pharmacological characterization of a ...potent, highly selective and orally active ROCK inhibitor, the derivative of a class of azaindoles, azaindole 1(6‐chloro‐N
4‐{3,5‐difluoro‐4‐(3‐methyl‐1H‐pyrrolo2,3‐bpyridin‐4‐yl)oxy‐phenyl}pyrimidine‐2,4‐diamine).
Experimental approach:
Pharmacological characterization of azaindole 1was performed with human recombinant ROCK in vitro. Vasodilator activity was determined using isolated vessels in vitro and different animal models in vivo.
Key results:
This compound inhibited the ROCK‐1 and ROCK‐2 isoenzymes with IC50 s of 0.6 and 1.1 nM in an ATP‐competitive manner. Although ATP‐competitive, azaindole 1was inactive against 89 kinases (IC50>10 μM) and showed only weak activity against an additional 21 different kinases (IC50=1 ‐ 10 μM). Only the kinases TRK und FLT3 were inhibited by azaindole 1in the sub‐micromolar range, albeit with IC50 values of 252 and 303 nM, respectively. In vivo, azaindole 1lowered blood pressure dose‐dependently after i.v. administration in anaesthetized normotensive rats. In conscious normotensive and spontaneously hypertensive rats azaindole 1induced a dose‐dependent decrease in blood pressure after oral administration without inducing a significant reflex increase in heart rate. In anaesthetized dogs, azaindole 1induced vasodilatation with a moderately elevated heart rate.
Conclusions and implications:
Azaindole 1is representative of a new class of selective and potent ROCK inhibitors and is a valuable tool for the elucidation of the role of ROCK in the cardiovascular system.
British Journal of Pharmacology (2007) 152, 1070–1080; doi:10.1038/sj.bjp.0707484; published online 15 October 2007
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.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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.
Myocytes isolated from the rat left ventricle were investigated by the whole-cell patch-clamp technique and single-cell RT-PCR.
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.
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.
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