Hydrolysis by phospholipase C (PLC) of phosphatidylinositol 4,5-bisphosphate is a key mechanism by which many extracellular signalling molecules regulate functions of their target cells. At least eight distinct isozymes of PLC are recognized in mammalian cells. Receptor-controlled PLC is often regulated by G proteins, which can be modified by pertussis toxin in some cells but not in others. In the latter cells, PLC-beta 1, but not PLC-gamma 1 or PLC-delta 1, may be activated by members of the alpha q-subfamily of the G protein alpha-subunits. An unidentified PLC in soluble fractions of cultured human HL-60 granulocytes is specifically stimulated by G protein beta gamma subunits purified from retina and brain. Identification of a second PLC-beta complementary DNA (PLC-beta 2) in an HL-60 cell cDNA library prompted us to investigate the effect of purified G protein beta gamma subunits on the activities of PLC-beta 1 and PLC-beta 2 transiently expressed in cultured mammalian cells. We report here that PLC-beta 1 and PLC-beta 2 were stimulated by free beta gamma subunits and that PLC-beta 2 was the most sensitive to beta gamma stimulation. Thus stimulation of PLC by beta gamma subunits is isozyme-selective and PLC-beta 2 is a prime target of beta gamma stimulation. Activation of PLC-beta 2 by beta gamma subunits may be an important mechanism by which pertussis toxin-sensitive G proteins stimulate PLC.

Insulin-induced upregulation of the AT1 receptor by posttranscriptional mechanisms may explain the association of hyperinsulinemia with hypertension and arteriosclerosis, because activation of the AT1 receptor plays a key role in the regulation of blood pressure and fluid homeostasis.

(Circulation 1990;82:1249-1265 H eart failure is characterized as inadequate cardiac output during exercise or rest, which is accompanied by a number of compensatory mechanisms. One of these is the activation of the sympathetic nervous system' to maintain cardiac output and perfusion pressure. The consequences of these processes are increased levels of catecholamines in the blood,2-4 which are related to the severity of symptoms and prognosis3 of patients with heart failure. The increased sympathetic tone imposes a permanent 83-adrenergic stimulus upon the heart, which leads to downregulation of cardiac ,8-adrenoceptors5-7 and a blunted positive inotropic response to 3-adrenoceptor agonists.5-10 There is also a reduced responsiveness of the failing myocardium to other cAMP-dependent positive inotropic compounds, such as phosphodiesterase inhibitors8-10

The present study demonstrates changes in the ET-receptor expression pattern in favor of the ETA receptor in human end-stage heart failure. Furthermore, activation of the cardiac ET system with increased tissue ET-1 concentrations in the failing myocardium is observed. This is more likely due to decreased clearance than to increased synthesis, because ppET-1 gene expression and ECE activity are unchanged.

Platelet-derived growth factor (PDGF) plays a critical role in the pathogenesis of proliferative diseases. NAD(P)H oxidase (Nox)-derived reactive oxygen species (ROS) are essential for signal transduction by growth factor receptors. Here we investigated the dependence of PDGF-AA-induced ROS production on the cytosolic Nox subunits Rac-1 and p47 phox , and we systematically evaluated the signal relay mechanisms by which the ␣PDGF receptor (␣PDGFR) induces ROS liberation. Stimulation of the ␣PDGFR led to a time-dependent increase of intracellular ROS levels in fibroblasts. Pharmacological inhibitor experiments and enzyme activity assays disclosed Nox as the source of ROS. ␣PDGFR activation is rapidly followed by the translocation of p47 phox and Rac-1 from the cytosol to the cell membrane. Experiments performed in p47 phox (؊/؊) cells and inhibition of Rac-1 or overexpression of dominant-negative Rac revealed that these Nox subunits are required for PDGFdependent Nox activation and ROS liberation. To evaluate the signaling pathway mediating PDGF-AA-dependent ROS production, we investigated Ph cells expressing mutant ␣PDGFRs that lack specific binding sites for ␣PDGFR-associated signaling molecules (Src, phosphatidylinositol 3-kinase (PI3K), phospholipase C␥, and SHP-2). Lack of PI3K signaling (but not Src, phospholipase C␥, or SHP-2) completely abolished PDGF-dependent p47 phox and Rac-1 translocation, increase of Nox activity, and ROS production. Conversely, a mutant ␣PDGFR able to activate only PI3K was sufficient to mediate these subcellular events. Furthermore, the catalytic PI3K subunit p110␣ (but not p110␤) was identified as the crucial isoform that elicits ␣PDGFR-mediated production of ROS. Finally, bromodeoxyuridine incorporation and chemotaxis assays revealed that the lack of ROS liberation blunted PDGF-AA-dependent chemotaxis but not cell cycle progression. We conclude that PI3K/p110␣ mediates growth factor-dependent ROS production by recruiting p47 phox and Rac-1 to the cell membrane, thereby assembling the active Nox complex. ROS are required for PDGF-AA-dependent chemotaxis but not proliferation.

We describe the first known case of a device-related bloodstream infection caused by Staphylococcus aureus small colony variants. Recurrent pacemaker-related bloodstream infection within a 7-month period illustrates the poor clinical and microbiologic response to prolonged antimicrobial therapy in a patient infected with this S. aureus subpopulation. Infections caused by Staphylococcus aureus range from mild skin infections to acute life-threatening diseases such as pneumonia, osteomyelitis, and endocarditis. However, S. aureus may also cause a chronic disease with persistent and recurrent infections. Skin and soft tissue infections, chronic osteomyelitis, and persistent infections in patients with cystic fibrosis have been associated with small colony variants, a naturally occurring subpopulation of the species S. aureus (1-6). S. aureus small colony variants are characterized as electron transport deficient bacteria because of their auxotrophism to hemin or menadione or are recognized as thymidine-dependent. These variants produce very small, mostly nonpigmented and nonhemolytic colonies. In addition, they also demonstrate various other features that are atypical for S. aureus, including reduced coagulase production, failure to use mannitol, and increased resistance to aminoglycosides and cell-wall active antibiotics (3-10). Furthermore, the ability of these variants to persist intracellularly within nonprofessional phagocytes has been described (3,5,11). Because of their fastidious growth characteristics and unusual morphologic appearance, small colony variants present a challenge both to the microbiologist and the clinician, often resulting in misidentification and misinterpretation (1,2,7,8). Prerequisite for recovering and identifying these variants is the application of extended conventional culture and identification techniques (3,5,8). We report the first case of a pacemaker-related bloodstream infection caused by S. aureus small colony variants. This case illustrates the poor clinical and microbiologic response to prolonged antimicrobial therapy in patients infected with these variants. Case ReportA 63-year-old man was transferred to our facility with the presumptive diagnosis of endocarditis related to a pacemaker-lead infection. Past medical history included hypertension, coronary artery disease, and noninsulindependent diabetes mellitus. A VVI (ventricular ventricular inhibited) pacemaker had been implanted for treatment of sick sinus syndrome 9 years earlier. Six weeks before admission, this device had been removed because of a pocket infection after blunt trauma with dislocation of the device and perforation of the skin. Specimens for microbiologic culture were not obtained at this time. The pacemaker leads were left in place, a gentamicin-containing sponge was applied to the infection site, and a new pacemaker was implanted on the other side of the chest. Four weeks later, the patient sought treatment at the local hospital for a high fever (39.7°C) and chills and a subcutaneous abscess with oxaci...

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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.