St Andrew's COVID-19 Surgery Safety (StACS) study: Skin cancer.

BACKGROUND: Skin cancer represents the most common malignancy worldwide and it is imperative that we develop strategies to ensure safe and sustained delivery of cancer care which are resilient to the ongoing impact of COVID-19. OBJECTIVE: This study prospectively evaluates the COVID-19 related patient risk and skin cancer management at a single tertiary referral centre, which rapidly implemented national COVID-19 safety guidelines. METHOD: A prospective cohort study was performed in all patients who underwent surgery for elective skin cancer service management, during the UK COVID-19 pandemic peak (April-May 2020). 'Real-time' 30-day hospital database deceased data were collected. Random selection was undertaken for patients who either underwent operative (surgery group) management or remained on the waiting list (control group); these groups were also prospectively followed-up within a controlled cohort study design and telephoned at the end of June 2020 for the control group or 30 days post-operatively. RESULTS: Of the 767 patients who had operations, there were no COVID-19 related deaths. Both the surgery (n = 384) and control (n = 100) groups were matched for age, sex, ethnicity, BMI, presence of comorbidities, smoking and positive COVID-19 contact. There were no differences in post-operative versus any symptom development (1.3%, 5/384 vs. 4%, 4/100, p = 0.093), or proportion of positive tests (8.6%, 33/384 vs. 8%, 8/100; p = 0.849), between the surgery and control groups. CONCLUSION: These data support continued and safe service provision, and no increased risk to skin cancer patients who require surgical management, which is vital for continuation of cancer treatment in the context of a pandemic. LEVEL OF EVIDENCE: II.

Sulforaphane improves vascular reactivity in mouse and human arteries after "preeclamptic-like" injury.

INTRODUCTION: The widespread maternal endothelial dysfunction that underlies the manifestations of preeclampsia is thought to arise from excessive placental production of antiangiogenic factors and enhanced oxidative stress. Therefore, we assessed whether the natural antioxidant sulforaphane could improve vascular function. METHODS: Cell viability of human umbilical vein endothelial cells (HUVECs) was assessed after 24 or 48 h in normoxia (20% O2) or hypoxia (1% O2) with or without sulforaphane. To model vascular dysfunction associated with preeclampsia, mouse mesenteric arteries were incubated in trophoblast conditioned media (TCM), and human omental arteries incubated in preeclamptic explant media (PEM) with or without sulforaphane. Both media are rich in antiangiogenic compounds associated with preeclampsia. TCM was generated from primary cytotrophoblast cells from term placentae of normotensive, while PEM was generated from explants from preeclamptic women. Reactivity was assessed by wire myography. sulforaphane's actions as a vasodilator were also investigated. RESULTS: Under conditions of hypoxia, sulforaphane improved HUVEC viability. In mouse mesenteric arteries, sulforaphane reduced contraction evoked by potassium (p < 0.001), phenylephrine and endothelin 1 (all p < 0.001). Sulforaphane also inhibited Ca2+-induced contraction (p = 0.014). Sulforaphane prevented TCM-induced augmentation of phenylephrine and angiotensin II-mediated contraction of mouse mesenteric arteries. In human omental arteries, sulforaphane induced vasodilation (p < 0.001), and prevented PEM-induced endothelial dysfunction by restoring arterial sensitivity to the endothelium-dependent vasodilator bradykinin (p = 0.008). DISCUSSION: Sulforaphane causes relaxation in arteries and protects against arterial dysfunction induced by placental-derived antiangiogenic factors, which are known to contribute to the preeclampsia.

Vascular actions of relaxin: nitric oxide and beyond.

The peptide hormone relaxin regulates the essential maternal haemodynamic adaptations in early pregnancy through direct actions on the renal and systemic vasculature. These vascular actions of relaxin occur mainly through endothelium-derived NO-mediated vasodilator pathways and improvements in arterial compliance in small resistance-size arteries. This work catalysed a plethora of studies which revealed quite heterogeneous responses across the different regions of the vasculature, and also uncovered NO-independent mechanisms of relaxin action. In this review, we first describe the role of endogenous relaxin in maintaining normal vascular function, largely referring to work in pregnant and male relaxin-deficient animals. We then discuss the diversity of mechanisms mediating relaxin action in different vascular beds, including the involvement of prostanoids, VEGF, endothelium-derived hyperpolarisation and antioxidant activity in addition to the classic NO-mediated vasodilatory pathway. We conclude the review with current perspectives on the vascular remodelling capabilities of relaxin. LINKED ARTICLES: This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Nonlinear effects of potassium channel blockers on endothelium-dependent hyperpolarization.

In a number of published studies on endothelium-dependent hyperpolarization and relaxation, the results of the effects of K+ blockers have been difficult to interpret. When the effects of two blockers have been studied, often either blocker by itself had little effect, whereas the two blockers combined tended to abolish the responses. Explanations suggested in the literature include an unusual pharmacology of the K+ channels, and possible blocker binding interactions. In contrast, when we applied the same blockers to segments of small blood vessels under voltage clamp, the blockers reduced the endothelium-dependent K+ current in a linearly additive manner. Resolution of these contrasting results is important as endothelium-derived hyperpolarization (EDH) makes its greatest contribution to vasorelaxation in arterioles and small resistance arteries, where it can exert a significant role in tissue perfusion and blood pressure regulation. Furthermore, EDH is impaired in various diseases. Here, we consider why the voltage-clamp results differ from earlier free-running membrane potential and contractility studies. We fitted voltage-clamp-derived current-voltage relationships with mathematical functions and considered theoretically the effects of partial and total block of endothelium-derived K+ -currents on the membrane potential of small blood vessels. When the K+ -conductance was partially reduced, equivalent to applying a single blocker, the effect on EDH was small. Total block of the endothelium-dependent K+ conductance abolished the hyperpolarization, in agreement with various published studies. We conclude that nonlinear summation of the hyperpolarizing response evoked by endothelial stimulation can explain the variable effectiveness of individual K+ channel blockers on endothelium-dependent hyperpolarization and resulting relaxation.

Time-dependent activation of prostacyclin and nitric oxide pathways during continuous i.v. infusion of serelaxin (recombinant human H2 relaxin).

BACKGROUND AND PURPOSE: In the RELAX-AHF trial, a 48 h i.v. serelaxin infusion reduced systemic vascular resistance in patients with acute heart failure. Consistent with preclinical studies, serelaxin augments endothelial vasodilator function in rat mesenteric arteries. Little is known about the contribution of endothelium-derived relaxing factors after a longer duration of continuous serelaxin treatment. Here we have assessed vascular reactivity and mechanistic pathways in mesenteric arteries and veins and the aorta after 48 or 72 h continuous i.v. infusion of serelaxin. EXPERIMENTAL APPROACH: Male rats were infused with either placebo or serelaxin (13.3 µg·kg(-1) ·h(-1) ) via the jugular vein using osmotic minipumps. Vascular function was assessed using wire myography. Changes in gene and protein expression and 6-keto PGF1α levels were determined by quantitative PCR, Western blot and ELISA respectively. KEY RESULTS: Continuous i.v. serelaxin infusion augmented endothelium-dependent relaxation in arteries (mesenteric and aorta) but not in mesenteric veins. In mesenteric arteries, 48 h i.v. serelaxin infusion increased basal NOS activity, associated with increased endothelial NOS (eNOS) expression. Interestingly, phosphorylated-eNOS(Ser1177) , eNOS and basal NOS activity were reduced in mesenteric arteries following 72 h serelaxin treatment. At 72 h, serelaxin treatment improved bradykinin-mediated relaxation through COX2-derived PGI2 production. CONCLUSIONS AND IMPLICATIONS: Continuous i.v. serelaxin infusion enhanced endothelial vasodilator function in arteries but not in veins. The underlying mediator at 48 h was NO but there was a transition to PGI2 by 72 h. Activation of the PGI2 -dependent pathway is key to the prolonged vascular response to serelaxin treatment.

The free instep flap for palmar and digital resurfacing.

The palmar and digital volar skin is unique because of its glabrous nature, texture and light colour in all races. Any defect on the palmar surface not suitable for a homodigital or thenar flap remains a challenge for reconstructive surgeons. Various skin flaps have been described in the literature for palmar resurfacing. They all provide wound cover and may even match the contour satisfactorily, however, the colour and texture mismatch compromises the aesthetics of reconstruction. In our experience, the free instep flap is a more appropriate choice for palmar and volar digital resurfacing. It provides glabrous, potentially sensate, hairless skin with a better colour and texture match compared to conventional pedicled or free flaps in all cases. This paper describes our refined flap raising technique, the possibility of a neurotisation and discusses the role of the free instep flap for idealised digital and palmar resurfacing. It can provide a truly cosmetic microsurgical reconstructive option.

Glucocorticoid treatment does not alter early cardiac adaptations to growth restriction in preterm sheep fetuses.

OBJECTIVE: To study the consequences of glucocorticoid treatment in fetal growth restriction (FGR) on cardiac function. SETTING: Laboratory. SAMPLE: Sheep. METHODS: Growth restriction was induced in sheep fetuses using single umbilical artery ligation (SUAL) on days 105-110 of gestation (term 147). Control fetuses were not ligated. Betamethasone (BM) (11.4 mg intramuscularly) or saline was administered to ewes on days 5 and 6 after surgery. Ewes were anaesthetised on day 7, the fetuses were removed, and their hearts were mounted on a Langendorff apparatus. Balloon catheters were inserted into the right and left ventricles. OUTCOME MEASURES: Ventricular contractile function and infarct area following ischaemia/reperfusion. RESULTS: The SUAL resulted in FGR (body weight 77% of control). The FGR was associated with increases in basal left ventricular pressure development and rates of contraction and relaxation. Right ventricular contraction was unaffected. Following brief ischaemia/reperfusion, the infarct area in FGR hearts was increased four-fold compared with controls. Antenatal BM resulted in a proportional increase in heart size and coronary flow, especially in FGR fetuses, and left ventricular pressure and heart rate responses to ß-adrenoceptor activation were increased. CONCLUSIONS: Fetal hearts rapidly adapt to FGR to maintain substrate delivery to the brain and heart. The FGR greatly enhanced the area of ischaemia, with implications for susceptibility in postnatal life. Antenatal BM treatment does not interfere with these cardiac changes but appears to increase left ventricle ß-adrenoceptor responsiveness, which may render the offspring vulnerable to subsequent cardiac dysfunction.

Alcohol exposure during late gestation: multiple developmental outcomes in sheep.

Alcohol consumption during pregnancy remains common in many countries. Exposure to even low amounts of alcohol (i.e. ethanol) in pregnancy can lead to the heterogeneous fetal alcohol spectrum disorders (FASD), while heavy alcohol consumption can result in the fetal alcohol syndrome (FAS). FAS is characterized by cerebral dysfunction, growth restriction and craniofacial malformations. However, the effects of lower doses of alcohol during pregnancy, such as those that lead to FASD, are less well understood. In this article, we discuss the findings of recent studies performed in our laboratories on the effects of fetal alcohol exposure using sheep, in which we investigated the effects of late gestational alcohol exposure on the developing brain, arteries, kidneys, heart and lungs. Our studies indicate that alcohol exposure in late gestation can (1) affect cerebral white matter development and increase the risk of hemorrhage in the fetal brain, (2) cause left ventricular hypertrophy with evidence of altered cardiomyocyte maturation, (3) lead to a decrease in nephron number in the kidney, (4) cause altered arterial wall stiffness and endothelial and smooth muscle function and (5) result in altered surfactant protein mRNA expression, surfactant phospholipid composition and pro-inflammatory cytokine mRNA expression in the lung. These findings suggest that fetal alcohol exposure in late gestation can affect multiple organs, potentially increasing the risk of disease and organ dysfunction in later life.

Vascularised Achilles tendon graft reconstruction--by the tendon for the tendon.

The management of posterior heel defects whether the result of trauma or post-operative that result in a loss of the Achilles tendon and overlying skin is complex and challenging. Various techniques have been employed to reconstruct these compound defects often comprising of a free tissue transfer combined with a fascial tendon reconstruction. We present a single-stage method of Achilles tendon reconstruction based upon a local vascularised tendon graft combined with a free antero-lateral thigh flap transfer and a review of the current literature.

Free 'mini' groin flap for digital resurfacing.

Ten cases of post-traumatic skin and soft tissue loss over the digits were resurfaced by free 'mini' groin flap. Five patients had defects of the dorsum of the digit, three had proximal palmar defects, one patient had circumferential skin loss and one had multiple digital injuries. The flap was harvested from the contralateral groin using a two-team approach. The average size of the flap was 5.5 x 4.75 cm and the mean operating time was 2.45 hrs. All patients had physiotherapy within 48-72 hrs. There were no flap losses. Six patients were happy with the cosmetic result and did not require any further debulking. We recommend free tissue transfer for digital resurfacing specifically in moderate to large dorsal defects, proximal volar defects, circumferential skin loss and multiple digit injuries.

Early vitamin E supplementation attenuates diabetes-associated vascular dysfunction and the rise in protein kinase C-beta in mesenteric artery and ameliorates wall stiffness in femoral artery of Wistar rats.

AIMS/HYPOTHESIS: The impact of early vitamin E supplementation on vascular function in diabetes remains unresolved. Therefore, we examined the effects of vitamin E on functional and structural parameters and on chemical markers that are disturbed in diabetes in mesenteric and femoral arteries. METHODS: Segments of both arteries, taken from control and 8-week-old streptozotocin diabetic Wistar rats that were treated or not with vitamin E, were mounted on wire and pressure myographs, after which endothelium-dependent and -independent vasodilation was assessed. Passive mechanical wall properties and the localisation and levels of protein kinase C (PKC)-beta(2) and AGE were evaluated in these vessels. RESULTS: Vitamin E supplementation was associated with improved endothelium-dependent and -independent vasodilatation in mesenteric arteries from diabetic rats. Impaired endothelium-dependent vasodilatation in diabetic mesenteric vessels was associated with PKC-beta(2) up-regulation and this was prevented by vitamin E supplementation. Increased AGE accumulation and plasma isoprostane levels in diabetic rats were not changed by vitamin E. In the femoral artery, vitamin E supplementation had no effect on endothelium-dependent or -independent vasodilatation, but did prevent the wall stiffening associated with diabetes. CONCLUSIONS/INTERPRETATION: Early vitamin E supplementation has a beneficial effect on diabetes-induced endothelial dysfunction in resistance arteries. This benefit may arise from a direct effect on smooth muscle function, as a result of inhibition of the PKC-beta(2) isoform by vitamin E.

Comparison of effects of diabetes mellitus on an EDHF-dependent and an EDHF-independent artery.

The hypothesis tested in this study is that diabetes has a different impact on an artery in which endothelium-dependent responses derive from both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) compared with responses in which NO predominates and EDHF is absent. The streptozotocin-treated rat model of diabetes was used, and the arteries were mounted on a wire myograph. In mesenteric arteries depolarized and constricted with phenylephrine, acetylcholine evoked hyperpolarization (31 +/- 2 mV) and complete relaxation; these responses were attributed to EDHF and NO. In femoral arteries, acetylcholine evoked a small, NO-mediated hyperpolarization (5 +/- 1 mV) and incomplete relaxation. Bradykinin evoked NO-dependent responses in mesenteric arteries. Whereas diabetes significantly impaired the EDHF-dependent hyperpolarization and relaxation in mesenteric arteries, NO-dependent responses in femoral and mesenteric arteries were preserved. 1-Ethyl-2-benzimidazolinone evoked hyperpolarization and relaxation in mesenteric arteries, and this was impaired in diabetes. In conclusion, NO-dependent responses are preserved in diabetes, whereas endothelial responses-dependent upon EDHF appear to be impaired. The putative channels responsible for mediating the EDHF response may be altered in diabetes.

EDHF is not K+ but may be due to spread of current from the endothelium in guinea pig arterioles.

Endothelium-derived hyperpolarizing factor (EDHF)-attributed hyperpolarizations and relaxations were recorded simultaneously from submucosal arterioles of guinea pigs with the use of intracellular microelectrodes and a video-based system, respectively. Membrane currents were recorded from electrically short segments of arterioles under single-electrode voltage clamp. Substance P evoked an outward current with a current-voltage relationship that was well described by the Goldman-Hodgkin-Katz equation for a K+ current, consistent with the involvement of intermediate- and small-conductance Ca2+-activated K+ channels. 1-Ethyl-2-benzimidazolinone relaxed the arterioles and evoked hyperpolarizations that were blocked by charybdotoxin, but not by iberiotoxin. Application of K+ induced depolarization under conditions in which EDHF evoked hyperpolarization. The Ba2+-sensitive component of the K+-induced current was inwardly rectifying, in contrast to the outwardly rectifying current evoked by substance P. EDHF-attributed hyperpolarizations in dye-identified smooth muscle cells were indistinguishable from those recorded from dye-identified endothelial cells in the same arterioles. These results provide evidence that EDHF is not K+ but may involve electrotonic spread of hyperpolarization from the endothelial cells to the smooth muscle cells.

K+ currents underlying the action of endothelium-derived hyperpolarizing factor in guinea-pig, rat and human blood vessels.

Membrane currents attributed to endothelium-derived hyperpolarizing factor (EDHF) were recorded in short segments of submucosal arterioles of guinea-pigs using single microelectrode voltage clamp. The functional responses of arterioles and human subcutaneous, rat hepatic and guinea-pig coronary arteries were also assessed as changes in membrane potential recorded simultaneously with contractile activity. The current-voltage (I-V) relationship for the conductance due to EDHF displayed outward rectification with little voltage dependence. Components of the current were blocked by charybdotoxin (30-60 nM) and apamin (0.25-0.50 microM), which also blocked hyperpolarization and prevented EDHF-induced relaxation. The EDHF-induced current was insensitive to Ba2+ (20-100 microM) and/or ouabain (1 microM to 1 mM). In human subcutaneous arteries and guinea-pig coronary arteries and submucosal arterioles, the EDHF-induced responses were insensitive to Ba2+ and/or ouabain. Increasing [K+]o to 11-21 mM evoked depolarization under conditions in which EDHF evoked hyperpolarization. Responses to ACh, sympathetic nerve stimulation and action potentials were indistinguishable between dye-labelled smooth muscle and endothelial cells in arterioles. Action potentials in identified endothelial cells were always associated with constriction of the arterioles. 18beta-Glycyrrhetinic acid (30 microM) and carbenoxolone (100 microM) depolarized endothelial cells by 31 +/- 6 mV (n = 7 animals) and 33 +/- 4 mV (n = 5), respectively, inhibited action potentials in smooth muscle and endothelial cells and reduced the ACh-induced hyperpolarization of endothelial cells by 56 and 58 %, respectively. Thus, activation of outwardly rectifying K+ channels underlies the hyperpolarization and relaxation due to EDHF. These channels have properties similar to those of intermediate conductance (IKCa) and small conductance (SKCa) Ca2+-activated K+ channels. Strong electrical coupling between endothelial and smooth muscle cells implies that these two layers function as a single electrical syncytium. The non-specific effects of glycyrrhetinic acid precludes its use as an indicator of the involvement of gap junctions in EDHF-attributed responses. These conclusions are likely to apply to a variety of blood vessels including those of humans.

EDHF, NO and a prostanoid: hyperpolarization-dependent and -independent relaxation in guinea-pig arteries.

The contribution of endothelium-derived hyperpolarizing factor (EDHF), nitric oxide (NO) and a prostanoid (PG) to endothelium-dependent hyperpolarization and relaxation were assessed in coronary and mammary arteries of guinea-pigs by integration of the responses evoked during discrete applications of acetylcholine (ACh). The results of this integration approach were compared with those using traditional peak analysis methods. N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) and indomethacin (1 microM), alone or in combination, were without effect on peak hyperpolarizations or relaxations while they markedly reduced the integrated responses in both arteries. Integrated responses attributed to NO and PG were larger than those attributed to EDHF in the coronary artery (at 2 microM ACh, hyperpolarization (mV s): NO, 4200+/-91; PG, 5046+/-157; EDHF, 1532+/-94; relaxation (mN s mm(-1)): NO, 2488+/-122; PG, 2234+/-96; EDHF, 802+/-54). Integrated responses attributed to NO, PG and EDHF were similar in the mammary artery (at 2 microM ACh, hyperpolarization: NO, 347+/-69; PG, 217+/-49; EDHF, 310+/-63; relaxation: NO, 462+/-94; PG, 456+/-144; EDHF, 458+/-40). Gilbenclamide (1 microM) all but abolished the hyperpolarization attributable to NO and PG but not EDHF in both arteries allowing assessment of the role of the hyperpolarization in relaxation. Gilbenclamide was without effect on the integrated relaxation due to NO but significantly reduced the relaxation associated with PG in the two arteries. In conclusion, integration of the responses enabled a more complete assessment of the contribution of EDHF, NO and PG to endothelium-dependent responses, which were strikingly different in the two arteries. There is commonality in the role of hyperpolarization in relaxation in both arteries: EDHF-dependent relaxation is strongly dependent on hyperpolarization; hyperpolarization plays an important role in PG relaxation, whereas it has a small facilitatory role in NO-dependent relaxation.

Endothelium-dependent hyperpolarization in resting and depolarized mammary and coronary arteries of guinea-pigs.

1. The membrane potential responses in guinea-pig coronary and mammary arteries attributable to endothelium-derived nitric oxide (NO), prostaglandin (PG) and hyperpolarizing factor (EDHF), and to exogenous NO and the prostacyclin analogue, iloprost, were compared at rest and when depolarized with the thromboxane analogue, U46619. 2. In the coronary artery, stimulation of the endothelium with acetylcholine (ACh) evoked hyperpolarization attributable to NO and a PG with similar pD2s at rest and in the presence of U46619. However, in depolarized tissues, the pD2 of the response attributed to EDHF required a 10 fold lower concentration of ACh compared with at rest. 3. In the mammary artery, lower concentrations of ACh were required to evoke NO- and EDHF-dependent hyperpolarizations in depolarized mammary artery compared with at rest, while PG-dependent hyperpolarization did not occur until the concentration of ACh was increased some 10 fold both at rest and in U46619. 4. The smooth muscle of the coronary artery of guinea-pigs was some 4 fold more sensitive to exogenous NO and iloprost than was the mammary artery. 5. In conclusion, the membrane potential response in arteries at rest, that is, in the absence of constrictor, may be extrapolated to events in the presence of constrictor when NO and PG are under study. However, the sensitivity to ACh and the magnitude of the hyperpolarization attributed to EDHF obtained in tissues at rest may underestimate these parameters in depolarized tissues.

Pregnancy-induced decrease in evoked excitatory junction potentials in guinea pig uterine artery.

The effects of stimulating the intramural nerves on the membrane potential and tension in the uterine artery of virgin guinea pigs were compared with the responses during pregnancy. In all tissues the amplitude of the excitatory junction potential (EJP) increased as the stimulus voltage was increased. The rate of increase in EJP amplitude in tissues from virgin animals greatly exceeded that recorded in late pregnant tissues. EJPs were abolished by tetrodotoxin but were resistant to blockade by alpha-adrenoceptor antagonists. Stimulation of the nerves also evoked a slow depolarization and contraction which were abolished by both tetrodotoxin and alpha-adrenoceptor antagonists. The amplitudes of the depolarizations and contractions were not correlated. The role of EJPs and alpha-adrenoceptor activation in the control of vascular function is discussed. Fluorescence histochemistry revealed a decrease in the density of the catecholamine innervation that was correlated with a decrease in catecholamine content as pregnancy progressed. In addition, there appeared to be a difference in the arrangement of the fluorescent varicosities, with a shift from varicosities that were close to the outer layer of smooth muscle in virgin tissues to those that were more distantly dispersed in the adventitia during late pregnancy. The changes would be expected to reduce the effectiveness of vasoconstrictor drive to the uterine artery as pregnancy progresses.

Inwardly rectifying whole cell potassium current in human blood eosinophils.

1. Membrane currents were studied in single human blood eosinophils using the whole cell voltage clamp technique. The whole cell current-voltage relationship exhibited rectification about the membrane potential which followed the potassium equilibrium potential when [K+]o was raised. Elevation of [K+]o considerably potentiated inward current amplitude, and in some cells channel activity was discernible in the whole cell membrane current recordings. The single channel conductance was 24 +/- 1 pS ([K+]o, 100 mM; [K+]i, 140 mM), and eosinophils were found to have as few as three, and on average twenty, inward rectifier channels each. 2. The inward current was inhibited in a voltage-dependent manner by extracellular cations in order of potency Ba2+ > Cs+ > Na+. Intracellular acidification inhibited while alkalization augmented the inward current. Mg2+ contributed to rectification as dialysis with nominally Mg(2+)-free pipette solution was associated with an increase in the outward current during membrane polarization. 3. By reverse transcription-polymerase chain reaction (RT-PCR) using suitable primers on human eosinophils mRNA, an inward rectifier channel, Kir2.1, was identified, which is known from expression studies to have very similar properties to those found in this study. 4. Superoxide anion production or its stimulation by phorbol 12-myristate 13-acetate (PMA) was not significantly affected by depolarization with 140 mM [K+]o, or by 1 mM BaCl2. 5. It is concluded that the single channel currents and the whole cell current rectification observed in human blood eosinophils resulted from the presence of an inwardly rectifying potassium channel, probably Kir2.1.