Hydrogen Peroxide and Sodium Transport in the Lung and Kidney.

Renal and lung epithelial cells are exposed to some significant concentrations of H2O2. In urine it may reach 100 µM, while in the epithelial lining fluid in the lung it is estimated to be in micromolar to tens-micromolar range. Hydrogen peroxide has a stimulatory action on the epithelial sodium channel (ENaC) single-channel activity. It also increases stability of the channel at the membrane and slows down the transcription of the ENaC subunits. The expression and the activity of the channel may be inhibited in some other, likely higher, oxidative states of the cell. This review discusses the role and the origin of H2O2 in the lung and kidney. Concentration-dependent effects of hydrogen peroxide on ENaC and the mechanisms of its action have been summarized. This review also describes outlooks for future investigations linking oxidative stress, epithelial sodium transport, and lung and kidney function.

Collisional frequency shifts in 133Cs fountain clocks.

We present a theoretical analysis of the density dependent frequency shift in Cs fountain clocks using the highly constrained binary collision model described by Leo et al. [Phys. Rev. Lett. 85, 2721 (2000)]. We predict a reversal in the clock shift at temperatures near 0.08 microK. Our results show that s waves dominate the collision process. However, as a consequence of the large scattering lengths in Cs the clock shift is strongly temperature dependent and does not reach a constant Wigner-law value until temperatures are less than 0.1 nK.

Binding properties of beta-blockers at recombinant beta1-, beta2-, and beta3-adrenoceptors.

The human heart contains at least four distinct beta-adrenoceptor subtypes, three of which have been cloned. However, the binding properties of beta-blockers to the different beta-adrenoceptor subpopulations are not yet thoroughly characterized. Human beta1-, beta2- and beta3-adrenoceptors were expressed in COS-7 cells and [125I]iodocyanopindolol saturation binding, and competition experiments with commonly used beta-blockers were performed in the respective membrane preparations. Atenolol and metoprolol were about fivefold selective for beta1- versus beta2- and beta3-adrenoceptors. Bisoprolol was approximately 15-fold selective for beta1- versus beta2- and approximately 31-fold selective for beta1- versus beta3-adrenoceptors. Carvedilol was nonselective for any beta-adrenoceptor subtype. We conclude that the beta1-selectivities of atenolol, metoprolol, and bisoprolol are lower in COS cell membranes compared with previous investigations performed in native membranes. All beta-blockers investigated bind to beta3-adrenoceptors. Differential binding properties to beta3-adrenoceptors might imply different responses as to body weight, cardiac contractility, heart rate, and growth regulation. This might imply differential indications for the drugs investigated.

Differential regulation of phospholipase C-beta isozymes in cardiomyocyte hypertrophy.

Cardiac hypertrophy is a major predictor of heart failure and of morbidity and mortality in developed countries. Many hormones and growth factors induce cardiac hypertrophy via activation of members of the phospholipase C (PLC) family. The expression pattern of the PLCbeta isozyme subfamily was investigated in neonatal rat cardiomyocytes after stimulation with different hypertrophic stimuli. Under control conditions and after stimulation with norepinephrine, cardiomyocytes expressed similar amounts of PLCbeta3 mRNA. In the presence of fetal calf serum (FCS), additional expression of PLCbeta1 was induced. Growth hormone (GH) and insulin-like growth factor-I (IGF-I) both induced a substantial increase in PLCbeta3 mRNA expression. The response to GH could not be abolished by the IGF-I receptor blocker IGF-I analogue indicating an IGF-I-independent action of GH. The upregulation of PLCbeta3 by IGF-I was abolished by preincubation of cardiomyocytes with the IGF-I receptor antagonist IGF-I analogue, the tyrosine kinase inhibitor genistein, the extracellular signal-related kinase (ERK) inhibitor PD 98059, the phosphatidylinositol-3- (PI-3) kinase inhibitor wortmannin and the p70 S6 kinase inhibitor rapamycin. Induction of the immediate early genes c-myc, c-fos, and c-jun by IGF-I was abolished by preincubation with antisense oligos against PLCbeta3. It is concluded that the expression of PLCbeta isozymes in cardiomyocytes is differentially regulated by different hypertrophic stimuli. The upregulation of PLCbeta3 by IGF-I is dependent on the activity of tyrosine kinase, ERK, PI3 kinase, and p70 S6 kinase and PLCbeta3 expression seems to be required for the induction of immediate early genes by IGF-I. The involvement of the PLCbeta subfamily in signal transduction of receptors other than G-protein-coupled receptors is suggested.

Beneficial effects of amiodarone in heart failure: interaction with beta-adrenoceptors rather than G proteins.

The effect of the antiarrhythmic drug amiodarone on the human myocardial beta-adrenoceptor-G protein-adenylyl cyclase signalling cascade was investigated. Amiodarone had no effect on myocardial G proteins and maximal adenylyl cyclase activity, but acted as a beta-adrenoceptor antagonist. This mechanism might be at least partially responsible for the beneficial effects of the drug in patients with arrhythmia and heart failure.

Guanine nucleotide binding proteins in cultured renal epithelia: studies with pertussis toxin and aldosterone.

The GTP-binding proteins from cultured A6 epithelia were examined in isolated membrane preparations. Binding of [35S]GTPgammaS revealed a class of binding sites with an apparent Kd value of 100 nM and a Bmax of 220 pmol/mg protein. Short-term aldosterone treatment of the cells did not modify the binding kinetics, whereas pertussis toxin (PTX) decreased Bmax by 50%. The mRNA levels for Galphai-3, Galpha0, Galphas, and Galphaq were not increased after aldosterone. The patterns of small Mr G proteins and of PTX-ribosylated proteins were identical in membranes of both control and aldosterone-treated cells. Cross-linking of [alpha-32P]GTP, in control membranes, showed either no labeling or a faint band of Mr 59.5 kDa. This protein became prominent after aldosterone, and its labeling decreased with spironolactone. Thus short-term aldosterone does not promote increased expression of known heterotrimeric G proteins in epithelial membranes but activates resident PTX-sensitive Gi proteins and stimulates the expression of a specific GTP-binding protein of Mr 59.5 kDa.

[Hormone therapy in heart failure: growth hormone and insulin-like growth factor I]. / Hormontherapie bei Herzinsuffizienz: Wachstumshormon und Insulin-like growth factor-I.

Heart disease is the major cause of mortality in the developed world. Despite recent advances in the therapy of heart failure due to ACE inhibitors and beta-blockers, the prognosis of this syndrome is still poor. In the past few years, the effects of growth hormone (GH) and insulin-like growth factor-I (IGF-I) on heart morphology and function were extensively studied. Some studies dealing with experimental heart failure of animals and one controversial study dealing with human heart failure suggest positive hemodynamic effects of GH and/or IGF-I treatment. This review summarizes the physiological effects of GH/IGF-I on the myocardium, their signal transduction mechanisms, and the data currently available on the therapeutic use of these agents.

Aldosterone stimulation of GTP hydrolysis in membranes from renal epithelia.

Specific hydrolysis of GTP catalyzed by membranes prepared from A6 epithelial cells grown on porous supports was measured. Aldosterone treatment of the cells for 4 h increased Na+ transport and stimulated GTP hydrolysis by apical membranes in vitro more than twofold over basal levels. This stimulation was attributed to an increase in maximum velocity with little change in Michaelis-Menten constant values. Na+ transport rate and GTP hydrolysis were linearly correlated after aldosterone. This relationship was maintained when aldosterone's response was blunted by various inhibitors. Spironolactone decreased both the hormone-stimulated guanosinetriphosphatase (GTPase) and the Na+ transport rate. Pertussis toxin, which exerted minimal effects on basal rates, reduced the increase of Na+ current normally observed after aldosterone and the hormone stimulation of GTPase activity. The expression of classical Gi/Go-type G proteins was not increased after hormone treatment. When A6 cells were grown on nonporous plastic dishes, aldosterone neither stimulated GTPase activity nor increased amiloride-blockable 22Na+ fluxes. We propose that activation of one or more G proteins in the apical membrane of A6 cells is directly involved in the natriferic action of aldosterone.