Csilla Hably

Role of Nox2 in elimination of microorganisms.

NADPH oxidase of the phagocytic cells (Nox2) transfers electrons from cytosolic NADPH to molecular oxygen in the extracellular or intraphagosomal space. The produced superoxide anion (O2·−) provides the source for formation of all toxic oxygen derivatives, but continuous O2·− generation depends on adequate charge compensation. The vital role of Nox2 in efficient elimination of microorganisms is clearly indicated by human pathology as insufficient activity of the enzyme results in severe, recurrent bacterial infections, the typical symptoms of chronic granulomatous disease. The goals of this contribution are to provide critical review of the Nox2-dependent cellular processes that potentially contribute to bacterial killing and degradation and to indicate possible targets of pharmacological interventions.

Consequences of the electrogenic function of the phagocytic NADPH oxidase

NADPH oxidase of phagocytic cells transfers a single electron from intracellular NADPH to extracellular O2, producing superoxide , the precursor to several other reactive oxygen species. The finding that a genetic defect of the enzyme causes chronic granulomatous disease (CGD), characterized by recurrent severe bacterial infections, linked generation to destruction of potentially pathogenic micro-organisms. In this review, we focus on the consequences of the electrogenic functioning of NADPH oxidase. We show that enzyme activity depends on the possibilities for compensating charge movements. In resting neutrophils K+ conductance dominates, but upon activation the plasma membrane rapidly depolarizes beyond the opening threshold of voltage-gated H+ channels and H+ efflux becomes the major charge compensating factor. K+ release is likely to contribute to the killing of certain bacteria but complete elimination only occurs if production can proceed at full capacity. Finally, the reversed membrane potential of activated neutrophils inhibits Ca2+ entry, thereby preventing overloading the cells with Ca2+. Absence of this limiting mechanism in CGD cells may contribute to the pathogenesis of the disease.

Effect of nitric oxide synthase inhibition on renal circulation and excretory function in anaesthetized rats.

The effects of nitric oxide synthase (NOS) inhibition (effected using L‐NAME, 14 mg (kg body mass (BM))‐1, administered intravenously) on systemic and renal circulation and renal excretory function has been investigated in anaesthetized Wistar rats subjected to one of two different degrees of isotonic extracellular (EC) volume expansion (40 and 60 ml kg‐1 (240 min)‐1). The administration of L‐NAME resulted in an increase in mean arterial blood pressure and total peripheral vascular resistance (TPR), and a significant reduction in cardiac output (CO) and the kidney fraction of CO in both experimental groups. The total renal blood flow (RBF) dropped from 557 ± 43.4 to 149 ± 13.1 ml min‐1 (100 g BM)‐1 and from 592 ± 45.9 to 191 ± 16.3 ml min‐1 (100 g BM)‐1 in the 40 and 60 ml kg‐1 (240 min)‐1 experimental volume expansion groups, respectively. A redistribution of the intrarenal circulation from the medulla of the kidney toward the cortex may have occurred. The NOS inhibition induced a significant decrease in the glomerular filtration rate (GFR; from 1.18 ± 0.10 to 0.53 ± 0.08 ml min‐1 (100 g BM)‐1 and from 1.26 ± 0.07 to 0.73 ± 0.08 ml min‐1 (100 g BM)‐1 in the 40 and 60 ml kg‐1 (240 min)‐1 experimental volume expansion groups, respectively), and the filtration fraction increased. The urine excretion dropped in parallel with the GFR, while the reduction in sodium and potassium excretion was more marked than that of the GFR, raising the possibility of a direct effect on the kidney tubules. The difference in EC volume expansion (the calculated increases in the EC volume in the last 90 min were 1.30 and 5.44% in the two time control groups and 3.66 and 7.45% in the two L‐NAME‐treated groups) did not induce any significant modification of the L‐NAME effect.

Intrarenal Distribution of Blood Flow in Sodium Depleted and Sodium Loaded Rats: Role of Nitric Oxide

The renal hemodynamic effects of nitric oxide synthase (NOS) inhibition and dietary salt were studied in rats. L-NAME (0.1 mg/ml in the drinking fluid, about 12 mg/kg/day) was given for 4 days to rats receiving low (sodium depletion, SD), normal (N) or high (sodium load, SL) NaCl diet. Intrarenal hemodynamics was studied in anaesthesia. NOS inhibition decreased renal blood flow and increased renal vascular resistance in each group. Cortical and outer medullary but not inner medullary blood flow increased in direct ratio to the sodium intake. NOS inhibition decreased the blood flow and increased the vascular resistance in all layers of the kidney in SD, N, and SL rats as well. In SD and N, but not in SL rats L-NAME induced vasoconstriction was higher in the outer (OM) and inner medulla (IM) than in the cortex (C) [SD: ΔCVR 43%, ΔOMVR 54%, ΔIMVR 84%; N: ΔCVR 54%, ΔOMVR 96%, ΔIMVR 106%; SL: ΔCVR 50%, ΔOMVR 64%, ΔIMVR 35%]; in normal rats blood flow shifts from the medulla toward the cortex. In conclusion, nitric oxide may have a role in the regulation of renal vascular tone not only in the case of regular sodium uptake but in the sodium depleted or loaded organism as well. However, nitric oxide has no role in the dietary salt evoked vascular adaptation in the kidney.

Role of nitric oxide in the regulation of blood flow in the rat submandibular gland during carotid artery occlusion

The possible involvement of nitric oxide in the preservation of blood flow to the rat submandibular gland after uni- or bilateral occlusion of the common carotid was studied. Glandular blood flow and mean blood pressure were monitored before, during and after carotid occlusion in the presence and absence of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine-methyl-ester (L-NAME). To calculate vascular resistance, the local perfusion pressure distal to the point of occlusion was also measured. In normal rats, uni- or bilateral carotid occlusion resulted in an immediate decrease in ipsilateral glandular blood flow. After the cessation of carotid occlusion, hyperaemia was observed in the submandibular gland. Both local perfusion pressure and vascular resistance decreased during carotid occlusion. In the group pretreated with L-NAME, trends in blood-flow responses to uni- or bilateral occlusion were identical to those registered in the control groups, though the magnitude of the alterations was significantly less. The well-maintained glandular blood flow was due to functioning vascular anastomoses and compensating dilatation of glandular blood vessels. Nitric oxide had only a restrained effect on this compensatory mechanism.

Angiotensin Ii Type 1 (at1) Receptor Blockade Enhances the L‐NAME‐Induced Vasoconstriction in Rat Submandibular Gland

The vasoregulatory role of nitric oxide (NO) and angiotensin II type 1 (AT1) receptors in the circulation of the submandibular gland (SMG) of rats was studied. The glandular blood flow was determined by means of laser Doppler flowmetry and rubidium isotope technique. The data obtained by these two methods correlated well (r= 0.77; P < 0.01). The AT1 receptor antagonist candesartan (0.5 mg kg−1, I.V.) reduced the vascular resistance in the SMG by 37% (P < 0.05). By contrast, the NO synthase blocker L‐NAME (15 mg kg−1, I.V.) significantly increased vascular resistance in the SMG both in candesartan‐treated (P < 0.001) and non‐treated (P < 0.001) animals. The increase in resistance was greater (P < 0.05) after previous blockade of AT1 receptors. These findings suggest that the AT1 receptors have an important role in the vasoregulation of the SMG in the rat. As a result of AT1 blockade, NO‐dependent tone of glandular vessels may be enhanced significantly.

Prof. Jiří Heller

Accessible online at: www.karger.com/journals/kbr Let us share our thoughts on Prof. Jiřı́ Heller who deceased after a long, serious disease in Prague on February 23, 2001. Prof. Heller graduated from Charles University School of Medicine in 1956 and went to work as a lecturer at the Institute of Physiology (where he had been a research student in the renal physiology laboratory since 1952). In 1962, he presented his thesis which earned him a PhD degree. The thesis, entitled ‘On the mechanism of reflexmediated changes in diuresis’, predicted the existence of atrial natriuretic factor and well reflected his talent for a career in science and experimental work. Regrettably, for political reasons, the thesis appeared only in the Czech language and never received worldwide publicity. After his forced departure from the medical school, he took the position of researcher at the Institute of Occupational Hygiene and Disease focusing his attention, between 1962 and 1966, on the mechanism of elimination of heavy metals by the kidney. In 1965, he spent a year as a fellowship student at the Department of Physiology, Free University in Berlin, Germany, mastering the technique of renal tubule micropuncture. Upon his return, he took the offer from Prof. Jan Brod to join the Institute for Circulatory Disease (which merged with other institutes in 1971 to form the Institute for Clinical and Experimental Medicine) and founded a laboratory of renal physiology where he actually worked until his death. It was in that laboratory that Prof. Heller introduced micropuncture techniques and carried out research into the regulation of renal hemodynamics. His pioneering work in this field won him international renown and his papers, published mainly in Pflüger’s Archiv, make up an integral part of the basics of renal physiology. Teaming up with his wife in the early 1980s, they bred a new model of the genetically hypertensive rat, referred to as the Prague hypertensive rat (PHR). The model is unique in that both the hypertensive and normotensive (Prague normotensive rat, PNR) lines originate from the same mating couple. The issue of hypertension became another main topic of research projects conducted by Prof. Heller; he initiated a number of pioneering projects (particularly in the field of transplant medicine) clearly demonstrating that hypertension in PHR ‘travels’ with the kidney, a finding which gave rise to the theory on the role played by the kidney in the development of hypertension. Prof. Heller worked in the laboratory and enjoyed performing experiments on his own. He loved the process of learning and getting to understand the way things actually work. He was also an excellent opponent, always seeking to help and getting to the core of the matter. However, he could be fairly blunt to clearly unprofessional and incompetent individuals, and never hesitated to let the person involved know. He never wasted his time in unfruitful discussions. Prof. Heller simply loved giving lectures and teaching medical students. He was the supervisor of several students during their postgraduate education programs and there is no doubt that some of them will carry on his research. He was a leader and a man of integrity who worked in his laboratory until the last minute, despite his losing battle with disease. We will all miss his charming personality, intellect, and his sense of humor.