Plastic physicians: The surgical salamanders of the COVID-19 pandemic

At the time of writing, coronavirus disease-2019 (COVID-19) has affected 6.42 million people globally and over 380,000 deaths, with the United Kingdom now having the highest death rate in Europe. The plastic surgery department at Leeds Teaching Hospitals put necessary steps in place to maintain an excellent urgent elective and acute service whilst also managing COVID-positive medical patients in the ward. We describe the structures and pathways implemented together with complex decision-making, which has allowed us to respond early and effectively. We hope these lessons will prove a useful tool as we look to open conversations around the recovery of normal activity.

Cortisol metabolism, postnatal depression and weight changes in the first 12 months postpartum

BACKGROUND & OBJECTIVES

Postnatal depression correlates with postpartum weight retention, and dysregulated cortisol metabolism is evident in depressed individuals. Cortisol metabolism, BMI and metabolic phenotype are robustly associated, but the role of cortisol metabolism in postnatal mental health and weight loss has never been examined.

DESIGN

A longitudinal observation.

PATIENTS

Forty nine healthy women with uncomplicated pregnancy.

MEASUREMENTS

BMI and urinary steroid metabolites at 1 week and 1, 3, 6 and 12 months postpartum. Validated urinary steroid metabolite ratios were measured to determine the activities of 11β-hydroxysteroid dehydrogenases (11β-HSD) that interconvert inactive cortisone and active cortisol and the 5α-reductases that clear cortisol to its inactive metabolites. Postnatal depression symptoms were measured at 1, 6 and 12 months.

RESULTS

Low 5α-reductase activity was associated with greater weight loss across the first year, independent of demographics, breastfeeding and depression. Postpartum BMI change was unrelated to postnatal depression at any time. Symptoms of postnatal depression were related to higher cortisol metabolite production at 12 months, independent of demographics and breastfeeding.

CONCLUSIONS

Greatest weight loss in the postpartum year was associated with lower conversion of cortisone to cortisol and lower conversion of cortisol to its metabolites, supporting previous work that demonstrates the facilitative role of lower 5α-reductase and 11β-HSD-1 in weight loss. Greater depression symptoms were associated with higher cortisol metabolite production rates. Whilst weight and mental health are both associated with dysregulation of the HPA axis, there may be different pathways towards depressed and obese phenotypes in healthy postpartum samples.

The corticosteroid metabolic profile of the mouse

Data are presented on the urinary corticosteroid metabolic profile of the mouse strain 129/svJ. Through the use of GC/MS we have characterized, or tentatively identified corticosterone (Kendall's compound B) metabolites of both the 11beta-hydroxy and 11-carbonyl (compound A) series in urine. Full mass spectra of the methyloxime-trimethylether derivatives of 15 metabolites are included in the paper as an aid to other researchers in the field. Metabolites ranged in polarity from tetrahydrocorticosterone (THB) to dihydroxy-corticosterone with dominance of highly polar steroids. We found that prior to excretion corticosterone can undergo oxidation at position 11beta, reduction at position 20 and A-ring reduction. Metabolites retaining the 3-oxo-4-ene structure can be hydroxylated at position 6beta- as well as at an unidentified position, probably 16alpha-. Saturated steroids can be hydroxylated at positions 1beta-, 6alpha-, 15alpha- and 16alpha. A pair of hydroxy-20-dihydro-corticosterone metabolites (OH-DHB) were the most important excretory products accounting for about 40% of the total. One metabolite of this type was identified as 6beta-hydroxy-DHB; the other, of similar quantitative importance was probably 16alpha-hydroxy-DHB. The ratio of metabolites of corticosterone (B) to those of 11-dehydro-corticosterone (A) was greater than 9:1, considerably higher than that for the equivalent "human" ratio of 1:1 for cortisol to cortisone metabolites. Results from this study allowed the evaluation of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) activity in mice with deleted glucose-6-phosphate transporter (G6PT). These mice had attenuated back-conversion of A to B resulting in an increased ratio of A-metabolites to B-metabolites [Walker EA, Ahmed A, Lavery GG, Tomlinson JW, Kim SY, Cooper MS, Stewart PM, 11beta-Hydroxysteroid dehydrogenase type 1 regulation by intracellular glucose-6-phosphate, provides evidence for a novel link between glucose metabolism and HPA axis function. J Biol Chem 2007;282:27030-6]. We believe this study is currently the most comprehensive on the urinary steroid metabolic profile of the mouse. Quantitatively less steroid is excreted in urine than in feces by this species but urine analysis is more straightforward and the hepatic metabolites are less subject to microbial degradation than if feces was analyzed.

Abnormal low-density lipoprotein subfraction profile in patients with untreated hypertension

BACKGROUND

Low-density lipoprotein (LDL) consists of a heterogeneous group of particles of varying size and electrophoretic mobility. A predominance of small, more mobile particles is a risk factor for cardiovascular disease.

AIM

To investigate the hypothesis that untreated patients with essential hypertension in the absence of vascular disease may exhibit abnormalities of LDL subfractions.

SETTING

Specialist hypertension clinic.

DESIGN

Cross-sectional study.

METHODS

Following disc polyacrylamide gel electrophoresis, the mean (LDL locus) and heterogeneity (LDL spread) of mobility was recorded in 41 patients (mean age 52.6 years, 24 men) presenting with untreated essential hypertension (in the absence of vascular disease or diabetes mellitus) and in 45 healthy controls (age 56.9 years, 22 men) recruited from primary-care lists.

RESULTS

Although there were no significant differences in total, low- or high-density lipoprotein cholesterol concentrations, LDL locus was significantly greater in the hypertensive group: mean (95%CI) 36.7 (35.7-37.6) vs. 34.8 (34.1-35.5), p=0.002. LDL locus was significantly elevated even in hypertensives with triglyceride concentrations below the median (<1.25 mmol/l). LDL spread was also greater in the hypertensive group, but not significantly: 5.6 (5.2-6.0) vs. 5.5 (5.3-5.8), p=0.10.

DISCUSSION

Hypertensive patients have a preponderance of smaller LDL subfractions. This dyslipidaemia is not readily detected by conventional lipid assays.

Dyslipidaemia in patients with malignant-phase hypertension

Low-density lipoprotein (LDL) consists of a heterogeneous group of particles of differing size, density and electrophoretic mobility, smaller particles being more atherogenic. A high proportion of small LDL particles is an independent risk factor for cardiovascular disease. We hypothesized that patients with malignant phase hypertension (MHT), the most severe form of hypertension, would demonstrate a more atherogenic LDL subfraction profile than either non-malignant hypertension (NMHT) or normotensive controls. We compared 16 patients with MHT to 41 patients with untreated NMHT and 45 normotensive controls. LDL subfraction profile was measured by disc polyacrylamide gel electrophoresis using a validated scoring system to calculate the mean size (locus) and heterogeneity (spread) of LDL subfraction mobilities. A higher LDL locus indicates a greater proportion of small LDL subfractions. LDL cholesterol levels were similar in all three groups (p=0.23). High-density lipoprotein cholesterol (HDL-C) levels were significantly lower (p<0.001) and serum triglyceride concentrations significantly higher (p=0.02) in the MHT group, compared to normotensive controls. LDL locus was greater in the NMHT group than in the normotensive controls and intermediate in the MHT group (p=0.008). There was no significant difference in LDL spread (p=0.26). Serum triglyceride concentrations were not significantly higher after adjusting for confounding variables. MHT is associated with an abnormal lipid profile, characterized by low HDL-cholesterol concentration. This dyslipidaemia may be partly responsible for the vascular complications and the poor prognosis of these patients.

Topical verapamil in glaucoma filtration surgery

PURPOSE

Because of the reported antifibroblastic effect of verapamil, a calcium-channel blocker, we investigated the potential benefit of adjunctive topical verapamil in patients undergoing glaucoma filtration surgery.

METHODS

This prospective, double-masked, randomized study included 56 eyes of 56 consecutive patients with chronic open-angle glaucoma undergoing trabeculectomy (primary or surgical revision of failed trabeculectomy), trabeculectomy combined with cataract surgery, or Molteno drainage device implantation. Postoperatively, the treated eyes received verapamil (0.25%) or one drop of placebo four times a day for 1 month in addition to 1% prednisolone four times a day and corticosteroid-antibiotic ophthalmic ointment at bedtime.

RESULTS

There were no significant differences in preoperative mean intraocular pressure, mean number of medications, and glaucoma severity between the verapamil and placebo groups. There were also no significant differences between the two groups in filtration success rate, mean intraocular pressure, and mean number of medications on postoperative days 1, 4, or 7 and at postoperative months 1, 2, 3, 4, 5, and 6 (P > 0.05).

CONCLUSION

There was no significant benefit of adjunctive topical verapamil when it was used after trabeculectomy, trabeculectomy combined with cataract surgery, or Molteno drainage device implantation.

Tumor cell invasion of model 3-dimensional matrices: demonstration of migratory pathways, collagen disruption, and intercellular cooperation

We report a novel 3-dimensional model for visualizing tumor cell migration across a nylon mesh-supported gelatin matrix. To visualize migration across these model barriers, cell proteolytic activity of the pericellular matrix was detected using Bodipy-BSA (fluorescent upon proteolysis) and DQ collagen (fluorescent upon collagenase activity). For 3-dimensional image reconstruction, multiple optical images at sequential z axis positions were deconvoluted by computer analysis. Specificity was indicated using well-known inhibitors. Using these fluorescent proteolysis markers and imaging methods, we have directly demonstrated proteolytic and collagenolytic activity during tumor cell invasion. Moreover, it is possible to visualize migratory pathways followed by tumor cells during matrix invasion. Using cells of differing invasive potentials (uPAR-negative T-47D wild-type and uPAR-positive T-47D A2--1 cells), we show that the presence of the T-47D-A2--1 cells facilitates the entry of T-47D wild-type cells into the matrix. In some cases, wild-type cells follow T-47D A2--1 cells into the matrix whereas other T-47D-wild-type cells appear to enter without the direct intervention of T-47D A2--1 cells. Thus, we have developed a new 3-dimensional model of tumor cell invasion, demonstrated protein and collagen disruption, mapped the pathways followed by tumor cells during migration through an extracellular matrix, and illustrated cross-talk among tumor cell populations during invasion.

Expression and permeation properties of the K(+) channel Kir7.1 in the retinal pigment epithelium

Bovine Kir7.1 clones were obtained from a retinal pigment epithelium (RPE)-subtracted cDNA library. Human RPE cDNA library screening resulted in clones encoding full-length human Kir7.1. Northern blot analysis indicated that bovine Kir7.1 is highly expressed in the RPE. Human Kir7.1 channels were expressed in Xenopus oocytes and studied using the two-electrode voltage-clamp technique. The macroscopic Kir7.1 conductance exhibited mild inward rectification and an inverse dependence on extracellular K+ concentration ([K+]o). The selectivity sequence based on permeability ratios was K+ (1.0) approximately Rb+ (0.89) > Cs+ (0.013) > Na+ (0.003) approximately Li+ (0.001) and the sequence based on conductance ratios was Rb+ (9.5) >> K+ (1.0) > Na+ (0.458) > Cs+ (0.331) > Li+ (0.139). Non-stationary noise analysis of Rb+ currents in cell-attached patches yielded a unitary conductance for Kir7.1 of approximately 2 pS. In whole-cell recordings from freshly isolated bovine RPE cells, the predominant current was a mild inwardly rectifying K+ current that exhibited an inverse dependence of conductance on [K+]o. The selectivity sequence based on permeability ratios was K+ (1.0) approximately Rb+ (0.89) > Cs+ (0.021) > Na+ (0.003) approximately Li+ (0.002) and the sequence based on conductance ratios was Rb+ (8.9) >> K+ (1.0) > Na+ (0.59) > Cs+ (0.23) > Li+ (0.08). In cell-attached recordings with Rb+ in the pipette, inwardly rectifying currents were observed in nine of 12 patches of RPE apical membrane but in only one of 13 basolateral membrane patches. Non-stationary noise analysis of Rb+ currents in cell-attached apical membrane patches yielded a unitary conductance for RPE Kir of approximately 2 pS. On the basis of this molecular and electrophysiological evidence, we conclude that Kir7.1 channel subunits comprise the K+ conductance of the RPE apical membrane.

Accreditation at the US EPA-NEIC. National Enforcement Investigations Center

The US Environmental Protection Agency-National Enforcement Investigations Center (NEIC) of Denver, Colorado is the specialty technical arm of the Office of Enforcement and Compliance Assurance (OECA) within the US EPA. NEIC is a center for technical support nationwide to state, local, tribal, and federal environmental enforcement and compliance assurance programs. NEIC is a source of expertise for technical analysis, compliance monitoring, engineering evaluations, forensic laboratory activities, information management, computer forensics, and witness testimony. Effective 1 February 2001, NEIC was granted accreditation for overall environmental measurement activities that include field sampling, field measurements and monitoring, and laboratory measurements. NEIC became the first and only environmental forensic center in the United States to be granted this type of accreditation. The accreditation criteria incorporates nationally and internationally accepted forensic and quality management standards. Awarded by the National Forensic Science Technology Center (NFSTC), the NEIC Accreditation Standard was developed for conducting environmental measurements while adhering to forensic requirements in specific areas. The NEIC Accreditation Standard is based on ISO/IEC Guide 25 and ANSI/ASQC E4-1994, and it references specific aspects of the American Society of Crime Laboratory Directors/Laboratory Accreditation Board (ASCLD/LAB) Manual.

Molecular cloning and expression of an inwardly rectifying K(+) channel from bovine corneal endothelial cells

PURPOSE

To determine the presence of a putative inwardly rectifying K(+) channel in bovine corneal endothelial (BCE) cells and to characterize its molecular and electrophysiological properties.

METHODS

An RT-PCR strategy was used to clone an IRK1 channel sequence from BCE mRNA. Northern blot analysis was used to confirm expression of this sequence in cultured BCE cells. Two-electrode voltage-clamp and whole-cell patch-clamp recordings were used to characterize the cloned channel expressed in Xenopus oocytes and the native channels in cultured BCE cells, respectively.

RESULTS

A full-length (1284 bp) coding sequence that shares 99.7% nucleotide sequence and 100% amino acid sequence identity to bovine lens IRK1 (Kir2.1) was cloned. The authors designate this sequence BCE IRK1 or BCIRK1. Northern blot analysis indicated that BCIRK1 mRNA is expressed in cultured BCE cells with two major transcripts of 7.5 and 5.5 kb. BCIRK1 cDNA was subcloned into the vector, pcDNA3.1(-), and cRNA transcribed from the BCIRK1 cDNA clone was injected into Xenopus oocytes. Two-electrode voltage-clamp recordings from injected oocytes revealed inwardly rectifying K(+) currents that were blocked by external Ba(2+) and Cs(+) in a concentration- and voltage-dependent manner. Whole-cell patch-clamp recordings from dissociated cultured BCE cells revealed strongly inwardly rectifying K(+) currents with similar properties.

CONCLUSIONS

Corneal endothelial cells express IRK1 (Kir2.1) inwardly rectifying K(+) channels. Consistent with the properties of IRK1 channels, BCIRK1 is likely involved in regulating membrane potential and possibly other cellular functions in corneal endothelial cells.

Cloning and functional expression of human retinal kir2.4, a pH-sensitive inwardly rectifying K(+) channel

To identify novel potassium channel genes expressed in the retina, we screened a human retina cDNA library with an EST sequence showing partial homology to inwardly rectifying potassium (Kir) channel genes. The isolated cDNA yielded a 2,961-base pair sequence with the predicted open reading frame showing strong homology to the rat Kir2. 4 (rKir2.4). Northern analysis of mRNA from human and bovine tissues showed preferential expression of Kir2.4 in the neural retina. In situ hybridization to sections of monkey retina detected Kir2.4 transcript in most retinal neurons. Somatic hybridization analysis and dual-color in situ hybridization to metaphase chromosomes mapped Kir2.4 to human chromosome 19 q13.1-q13.3. Expression of human Kir2. 4 cRNA in Xenopus oocytes generated strong, inwardly rectifying K(+) currents that were enhanced by extracellular alkalinization. We conclude that human Kir2.4 encodes an inwardly rectifying K(+) channel that is preferentially expressed in the neural retina and that is sensitive to physiological changes in extracellular pH.

Efficacy of apraclonidine 1% versus pilocarpine 4% for prophylaxis of intraocular pressure spike after argon laser trabeculoplasty

OBJECTIVE

The authors compared the efficacy of apraclonidine 1% versus pilocarpine 4% prophylaxis of post-argon laser trabeculoplasty (ALT) intraocular pressure (IOP) spike.

DESIGN

Prospective randomized clinical trial.

PARTICIPANTS

Two hundred twenty-eight eyes of 228 patients with primary open-angle glaucoma undergoing ALT were studied.

INTERVENTION

Patients were given 1 drop of either apraclonidine 1% (n = 114) or pilocarpine 4% (n = 114) 15 minutes before ALT.

MAIN OUTCOME MEASURES

Peri-ALT IOPs and incidences of post-ALT IOP spikes at 5 minutes, 1 hour, and 24 hours were compared between the two groups.

RESULTS

The two groups were similar in age, race, and medical dependency. Post-ALT mean IOPs at 5 minutes, 1 hour, and 24 hours were significantly lower than pre-ALT mean IOPs in both apraclonidine (P < 0.001) and pilocarpine (P < 0.001) groups. Incidences of IOP spikes greater than 1, 3, and 5 mmHg at 1 hour post-ALT were 21.1%, 14.9%, and 8.8% for the apraclonidine group and 12.3%, 5.3%, and 4.4% for the pilocarpine group (P = 0.076, 0.015, and 0.18 chi-square test). In the apraclonidine prophylaxis group, patients on long-term apraclonidine showed significantly higher incidence of post-ALT IOP spike than the patients without such long-term apraclonidine use (35.7%, 15 of 42 eyes, vs. 12.5%, 9 of 72 eyes; P = 0.003). In addition, peri-ALT pilocarpine prophylaxis tended to be less effective in patients undergoing long-term pilocarpine therapy but without statistical significance (17.4%, 8 of 46 eyes, vs. 9.4%, 6 of 64 eyes; P = 0.17).

CONCLUSION

Peri-ALT pilocarpine 4% was at least as effective as, if not more effective than, apraclonidine 1% in post-ALT IOP spike prophylaxis. Peri-ALT apraclonidine prophylaxis was not effective in patients on long-term apraclonidine, and peri-ALT pilocarpine prophylaxis tended to be less effective in patients undergoing long-term pilocarpine therapy. Pilocarpine 4% can be considered as a first-choice drug for post-ALT IOP spike prophylaxis, especially in patients under treatment with apraclonidine.

The additive effect of latanoprost to maximum-tolerated medications with low-dose, high-dose, or no pilocarpine therapy

OBJECTIVE

To assess the efficacy of latanoprost additive therapy in patients with intraocular pressure (IOP) out of control while taking maximum-tolerated medications and to determine whether pilocarpine therapy has a dose-dependent adverse effect on the efficacy of latanoprost therapy.

DESIGN

Noncomparative case series.

PARTICIPANTS

Sixty-one eyes of 61 patients with chronic glaucoma with IOP out of control while receiving maximum-tolerated medications were treated with latanoprost additive therapy on a compassionate basis.

MAIN OUTCOME MEASURES

Follow-up was up to 22 months with a mean of 13.9 +/- 5.7 months. Kaplan-Meier survival analysis with Mantel-Cox log-rank test was performed to determine the overall success of latanoprost additive therapy and to compare the success rates of high-dose pilocarpine, low-dose pilocarpine, and no pilocarpine therapies. The criterion for success was avoiding glaucoma surgery with IOP decrease of 20% or greater and final IOP less than 22 mmHg. The IOP change and its significance for patients satisfying and failing the criterion for success also were determined to assess the latanoprost additive therapy. In addition, a number of pretreatment variables, including pilocarpine therapy, were analyzed for a significant effect on the efficacy of latanoprost additive therapy using Cox proportional hazards regression analysis.

RESULTS

Latanoprost additive therapy significantly lowered mean IOP by 3.9 +/- 5.5 mmHg at 3 months and by 3.5 +/- 5.8 mmHg at 12 months. The cumulative success rate of the latanoprost additive therapy was 70% at 1 month, 42% at 3 months, 40% at 6 months, and 30% at 12 months. Of the variables studied, only increased number of previous incisional glaucoma surgeries and IOP greater than 24 mmHg before latanoprost additive therapy were significant prognostic factors for failure of latanoprost additive therapy. Pilocarpine therapy in any dose had no significant effect.

CONCLUSION

This study supports a trial of latanoprost additive therapy before glaucoma surgery in patients with IOP out of control while receiving maximum-tolerated medications irrespective of pilocarpine therapy and the pilocarpine dosage, especially when the number of previous incisional glaucoma surgery is less than three and the IOP is less than 25 mmHg.

ATP-dependent regulation of inwardly rectifying K+ current in bovine retinal pigment epithelial cells

Inwardly rectifying K+ current (IKir) in freshly isolated bovine retinal pigment epithelial (RPE) cells was studied in the whole cell recording configuration of the patch-clamp technique. When cells were dialyzed with pipette solution containing no ATP, IKir ran down completely in <10 min [half time (t1/2) = 1.9 min]. In contrast, dialysis with 2 mM ATP sustained IKir for 10 min or more. Rundown was also prevented with 4 mM GTP or ADP. When 0.5 mM ATP was used, IKir ran down by approximately 71%. Mg2+ was a critical cofactor because rundown occurred when the pipette solution contained 4 mM ATP but no Mg2+ (t1/2 = 1.8 min). IKir also ran down when the pipette solution contained 4 mM Mg2+ + 4 mM 5'-adenylylimidodiphosphate (t1/2 = 2.7 min) or 4 mM adenosine 5'-O-(3-thiotriphosphate) (t1/2 = 1.9 min), nonhydrolyzable and poorly hydrolyzable ATP analogs, respectively. We conclude that the sustained activity of IKir in bovine RPE requires intracellular MgATP and that the underlying mechanism may involve ATP hydrolysis.

Neuropeptide Y and the retinal pigment epithelium: receptor subtypes, signaling, and bioelectrical responses

PURPOSE

To characterize the potential for neuropeptide Y (NPY) signaling in the retinal pigment epithelium (RPE) by identifying the NPY receptor subtypes present, determining the effect of NPY on second-messenger production and membrane conductance, and establishing the neural retina as a site of NPY gene expression.

METHODS

Neuropeptide Y receptors present in bovine and human RPE were identified using ribonuclease protection assays and reverse transcriptase-coupled polymerase chain reaction. Assays of cyclic adenosine monophosphate (cAMP) and inositol phosphate production were performed using anion exchange chromatography and RPE cultures labeled with tritiated adenine or myo-inositol, respectively. Open-circuit recordings of transepithelial potential and resistance were performed using intact bovine RPE-choroid preparations. Neuropeptide Y-expressing cells in the retina were identified by staining for beta-galactosidase activity in eyes from mice in which lacZ replaces a portion of the NPY gene.

RESULTS

Human RPE contained transcripts encoding Y1, Y2, and Y5 receptors, the predominant subtypes present in the central nervous system. Bovine RPE contained transcripts encoding Y2 receptors but not Y1 receptors. However, cultured cells contained transcripts encoding Y1 and Y2 receptors. Neuropeptide Y signaling in cultured bovine RPE occurred predominately through the Y2 receptor subtype, because nanomolar amounts of NPY and NPY13-36, but not [Leu31,Pro34]NPY, significantly inhibited isoproterenol-induced cAMP accumulation. Apical application of NPY increased the transepithelial potential in RPE-choroid preparations. This response was greatly diminished after basolateral membrane Cl- channels were blocked or changes in intracellular Ca2+ concentration were prevented with a Ca2+ chelator. The NPY gene was expressed in amacrine cells of the inner nuclear and ganglion cell layers of the mouse retina.

CONCLUSIONS

The discovery of functionally coupled NPY receptors in the RPE represents the identification of a novel site of expression of this receptor family. The effects of NPY on the electrophysiologic properties of the bovine RPE are consistent with a potential paracrine role in regulating basolateral membrane Ca2+-sensitive Cl- conductance linked to Cl- and fluid transport.

Assessment of swelling-activated Cl- channels using the halide-sensitive fluorescent indicator 6-methoxy-N-(3-sulfopropyl)quinolinium

This study describes a quantitative analysis of the enhancement in anion permeability through swelling-activated Cl- channels, using the halide-sensitive fluorescent dye 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ). Cultured bovine corneal endothelial monolayers perfused with NO3- Ringer's were exposed to I- pulses under isosmotic and, subsequently, hyposmotic conditions. Changes in SPQ fluorescence due to I- influx were significantly faster under hyposmotic than under isosmotic conditions. Plasma membrane potential (Em) was -58 and -32 mV under isosmotic and hyposmotic conditions, respectively. An expression for the ratio of I- permeability under hyposmotic condition to that under isosmotic condition (termed enhancement ratio or ER) was derived by combining the Stern-Volmer equation (for modeling SPQ fluorescence quenching by I-) and the Goldman flux equation (for modeling the electrodiffusive unidirectional I- influx). The fluorescence values and slopes at the inflection points of the SPQ fluorescence profile during I- influx, together with Em under isosmotic and hyposmotic conditions, were used to calculate ER. Based on this approach, endothelial cells were shown to express swelling-activated Cl- channels with ER = 4.9 when the hyposmotic shock was 110 +/- 10 mosM. These results illustrate the application of the SPQ-based method for quantitative characterization of swelling-activated Cl- channels in monolayers.

Long-term outcome of primary glaucoma triple procedure with adjunctive 5-fluorouracil

PURPOSE

To evaluate the long-term effect of adjunctive subconjunctival 5-fluorouracil (5-FU) on the filtration outcome of primary glaucoma triple procedure (PGTP) in primary open-angle glaucoma (POAG) patients.

METHODS

Seventy-four POAG patients were randomly assigned to PGTP alone (36 patients) or PGTP with adjunctive subconjunctival 5-FU (5.0 +/- 1.3 injections of 5 mg each, total of 24.8 mg) (38 patients). After surgery, the patients were examined at regular intervals for intraocular pressure (IOP), visual acuity, medical therapy requirements, and complications. Surgical success was defined as IOP < or = 20 mmHg on postoperative medication < or = 1 without additional glaucoma surgery.

RESULTS

Over an average follow-up (+/- SD) of 45.3 +/- 25.0 months, both 5-FU and control groups maintained significant improvement of IOP control and visual acuity. However, there were no statistically significant differences between the 5-FU and control groups with respect to postoperative IOP, number of glaucoma medications, visual acuity outcome, and success rate overall or in selected patients with one or more of the risk factors for filtration failure.

CONCLUSIONS

The use of low-dose subconjunctival 5-FU (mean dosage of 24.8 mg in 5.0 +/- 1.3 injections) as an adjunct did not significantly improve the long-term filtration outcome of PGTP in POAG patients.

Limbus-based vs fornix-based conjunctival flap in combined glaucoma and cataract surgery with adjunctive mitomycin C

PURPOSE

To determine the efficacy and safety of limbus-based vs fornix-based conjunctival flaps in patients with primary open-angle glaucoma undergoing trabeculectomy combined with phacoemulsification and intraocular lens implantation with adjunctive subconjunctival mitomycin C.

METHODS

In a prospective study, 69 eyes of 69 patients with primary open-angle glaucoma, visually symptomatic cataracts, and no previous incisional ocular surgery were randomly assigned to limbus-based and fornix-based conjunctival flap groups. All patients received trabeculectomy combined with phacoemulsification and posterior chamber lens implantation with 1-minute (0.5 mg/ ml) application of subconjunctival mitomycin C.

RESULTS

The mean intraocular pressures were significantly (P < .05) lower on significantly (P < .05) fewer medications postoperatively at 1 week, 1 month, 3, 6, 9, 12, and 15 to 18 months, and at last follow-up in both groups than they had been preoperatively. However, there were no significant (P > .05) differences in postoperative mean intraocular pressure, mean number of medications, and visual acuity between the two groups at any time interval. Hypotony with wound leak was significantly (P = .019) higher in the limbus-based group. Other postoperative complications were not significantly (P > .05) different between the two groups.

CONCLUSIONS

There was no notable difference in glaucoma control or visual outcome between limbus-based and fornix-based conjunctival flaps in primary trabeculectomy combined with phacoemulsification and lens implantation with adjunctive subconjunctival mitomycin C. The fornix-based flap was as safe as, if not safer than, the limbus-based flap in the glaucoma triple procedure with adjunctive subconjunctival mitomycin C.

Primary glaucoma triple procedure in patients with primary open-angle glaucoma: the effect of mitomycin C in patients with and without prognostic factors for filtration failure

PURPOSE

To investigate the effect of adjunctive mitomycin C on primary glaucoma triple procedure in patients with primary open-angle glaucoma with and without one or more of the prognostic factors for filtration failure of primary glaucoma triple procedure. Those factors include being of African-American race, having a preoperative intraocular pressure of 20 mm Hg or more on maximum tolerated medications, and being on two or more medications preoperatively.

METHODS

Study patients consisted of 197 consecutive patients with primary open-angle glaucoma who were randomly assigned to receive either no adjunctive mitomycin C (101 eyes of 101 patients) or to receive adjunctive subconjunctival mitomycin C (96 eyes of 96 patients) during the primary glaucoma triple procedure. Kaplan-Meier survival analysis comparisons were made between respective subgroups with and without prognostic indicators for filtration failures using a relatively stringent set of criteria for filtration success of primary glaucoma triple procedure.

RESULTS

There was no statistically significant (P = .117) difference in filtration success of primary glaucoma triple procedure between the control and mitomycin C groups. Adjunctive mitomycin C significantly (P < .05) improved the filtration outcome of the primary glaucoma triple procedure in the subgroups with each of the three prognostic factors for filtration failure of primary glaucoma triple procedure. On the other hand, in the subgroups without the prognostic factors, adjunctive mitomycin C did not significantly (P > .05) change the filtration outcome of the primary glaucoma triple procedure.

CONCLUSION

These findings establish the basis for selective use of mitomycin C in patients with primary open-angle glaucoma undergoing primary glaucoma triple procedure.

Comparative study of silicone versus acrylic foldable lens implantation in primary glaucoma triple procedure

OBJECTIVE

To compare silicone versus acrylic foldable intraocular lens (IOL) implantation in primary glaucoma triple procedure (PGTP).

DESIGN

Prospective, randomized.

PARTICIPANTS

A total of 79 eyes of 79 primary open-angle glaucoma (POAG) patients in need of combined surgery were randomized to a silicone IOL group (36 eyes) and acrylic IOL group (43 eyes).

INTERVENTION

The study eyes underwent PGTP, which consisted of primary trabeculectomy, phacoemulsification, and posterior chamber IOL implantation. Adjunctive mitomycin C (MMC) (0.5 mg/ml for 1 minute) was used selectively only in patients with one or more risk factors for filtration failure of PGTP.

MAIN OUTCOME MEASURES

Snellen visual acuity, intraocular pressure (IOP), slit-lamp biomicroscopy, and number of glaucoma medications were measured, performed, or determined preoperatively and at regular intervals postoperatively.

RESULTS

There were no significant differences in the mean number of postoperative glaucoma medications at 1, 2, 3, 4-6, and 9-12 months and at last follow-up (P > 0.05); mean change in corrected visual acuity best attained (P = 0.315) or at last follow-up (P = 0.223) between the silicone and acrylic groups. Both groups had significant decreases in mean IOP and mean number of medications postoperatively at all times (P < 0.05). However, the postoperative IOP > 25 mmHg and IOP spike > 5 mmHg above preoperative IOP during the first month were significantly higher in the acrylic group (P = 0.026). The mean postoperative IOP at 1 month in the acrylic group was also significantly higher than the silicone group (14.1 +/- 5.0, 11.2 +/- 3.9, P = 0.005). Conversely, there were no significant differences in mean postoperative IOP at 2, 3, 4-6, and 9-12 months and at last follow-up between the silicone and acrylic groups (P > 0.05). Suture removal or release occurred significantly more frequently in the acrylic IOL group during the first month and the first 2 months (48.8% and 60.5%) than the silicone group (25.0% and 36.1%, P = 0.030 and 0.031, respectively). There were no significant differences in postoperative complications or surgical interventions between the two groups (P > 0.05).

CONCLUSIONS

During the first year following the PGTP with selective use of MMC, there were no significant differences in the medical dependency or visual outcomes or complications between the silicone and acrylic groups. Both groups attained significant decreases in IOP postoperatively. However, the mean IOP was significantly higher in the acrylic than the silicone group at 1 month postoperatively, and postoperative IOP > 25 mmHg and IOP spike > 5 mmHg above preoperative IOP were significantly greater in the acrylic group. There were significantly more suture releases in the acrylic IOL group than the silicone IOL group in the first 2 months postoperatively.

Isolated bovine retinal pigment epithelial cells express delayed rectifier type and M-type K+ currents

Outwardly rectifying K+ currents in freshly isolated bovine retinal pigment epithelial (RPE) cells were characterized using the whole cell and perforated-patch configurations of the patch-clamp technique. All cells exhibited a delayed rectifier type K+ current. This current had an activation threshold voltage of approximately -40 mV, activated with a sigmoidal trajectory, and inactivated completely over a period of several seconds. External tetraethylammonium (TEA) was an effective blocker of the delayed rectifier current [apparent dissociation constant (Kd) = 5.1 mM], but external Ba2+ was relatively ineffective. Approximately 24% of the cells also exhibited a sustained outwardly rectifying K+ current that became activated at voltages positive to approximately -80 mV. This current resembled the neuronal M-current. External Ba2+ was a potent blocker of this current (apparent Kd = 1.1 mM), but external TEA and Cs+ were relatively ineffective. These results indicate that freshly isolated bovine RPE cells express K+ currents of both the delayed rectifier and M types. The latter may contribute to the resting K+ conductances of the apical and basolateral membranes.

Analysis of reliability indices from Humphrey visual field tests in an urban glaucoma population

PURPOSE

Visual field assessment is extremely important in glaucoma management, but interpretation is affected by the quality of the patient's performance. The authors have investigated the reliability of visual field performance by a randomly selected sample of the chronic glaucoma population at an urban tertiary care practice.

METHODS

Patient reliability in Humphrey automated visual field testing was studied in 106 randomly selected chronic open-angle glaucoma patient charts, which provided 768 tests (mean, 7.2 +/- 4.8 fields; range, 2-18 fields). Reliability criteria were established as less than 20% fixation losses, less than 33% false-negative error, and less than 33% false-positive error, as recommended by Humphrey Instruments, Inc (San Leandro, CA).

RESULTS

Patients performed reliably in 61% of right eye fields, 58% of left eye fields, and 59.5% overall. Of the 106 patients, only 35 (33%) were always reliable in both eyes, whereas 8 (7.5%) were always unreliable in both eyes. The most common cause of unreliability was fixation loss (39%), whereas false-positive error (5%) and false-negative error (9%) were less frequent. A more severely depressed mean deviation correlated significantly with poorer performance on the three reliability indices, with false-negative error having the greatest correlation, followed by fixation loss and false-positive error. Corrected pattern standard deviation correlated closely only with false-negative error. Prolonged test time also correlated with all three reliability indices. Age was a significant factor for fixation loss but not for false-negative or false-positive error.

CONCLUSIONS

The authors conclude that fewer than two thirds of the Humphrey visual fields were reliable with the authors' urban tertiary care population of patients with glaucoma. Relaxing the fixation loss criterion to less than 33% improved the rate of reliability to approximately 75%. The severity of glaucomatous visual field defects, test time, and age were identified as factors influencing the reliability of the Humphrey visual fields.

Primary glaucoma triple procedure with or without adjunctive mitomycin. Prognostic factors for filtration failure

PURPOSE

The prerequisite for selective use of adjunctive mitomycin C (MMC) in primary glaucoma triple procedure (PGTP) is a better understanding of the prognostic factors. Therefore, the authors carried out the current study on the outcome of PGTP with and without adjunctive MMC to determine the prognostic factors for filtration failure of PGTP.

METHODS

The study patients consisted of 174 consecutive primary open-angle glaucoma (POAG) patients undergoing PGTP. They were assigned randomly to either no adjunctive MMC (93 eyes of 93 patients) or adjunctive subconjunctival MMC (81 eyes of 81 patients) during the PGTP. After surgery, the patients were examined at regular intervals for visual acuity, intraocular pressure (IOP) control, medical therapy requirements, and complications. Filtration failure was determined according to two different criteria: (1) a less stringent set of criteria (criterion I) and (2) a more stringent set of criteria (criterion II).

RESULTS

There were no statistically significant differences between the groups with and without adjunctive MMC with respect to postoperative IOP, number of medications, and visual acuity outcome during mean follow-up (+/- standard deviation) of 25.1 +/- 5.5 months (P > 0.05 for each). However, there were prognostic factors for filtration failure in the control group but not in the MMC group. Black race, diabetes mellitus, preoperative IOP greater than or equal to 20 mmHg, and number of preoperative medications greater than two were found to be significant prognostic factors for filtration failure by criterion I. Black race, preoperative IOP greater than or equal to 20 mmHg and number of preoperative medications greater than 1 were significant prognostic factors for filtration failure by criterion II.

CONCLUSION

There was no statistically significant difference in the overall outcome of PGTP between control and MMC groups of nonselected patients with primary open-angle glaucoma. Black race, diabetes mellitus (by criterion I only), preoperative IOP greater than or equal to 20 mmHg, and number of preoperative medications greater than 2 (by criterion I) or greater than 1 (by criterion II) were found to be significant independent prognostic factors for filtration failure of PGTP without adjunctive MMC but no with adjunctive MMC. The use of adjunctive subconjunctival MMC in PGTP may have to be selective, primarily in those patients with primary open-angle glaucoma with one or more of the prognostic factors for filtration failure.

Use of fascia lata in revision of filtration surgery

PURPOSE

To report on a successful use of fascia lata patch graft in revision of trabeculectomy for management of severe chronic discomfort associated with an exuberant conjunctival filtering bleb over a very nasal filtering site.

METHODS

After dissecting a conjunctival flap over the area of the trabeculectomy at the nasal quadrant, fascia lata patch graft was sutured in place over the filtering site when primary suture closure was found ineffective. A new trabeculectomy was performed temporal and superior to the old site, and the conjunctival wound closed watertight.

RESULTS

The fascia lata patch graft was effective in closing the filtration over the old trabeculectomy site at the nasal quadrant, and a new filtering bleb developed superiorly over the new trabeculectomy site, resulting in sustained IOP control.

CONCLUSION

Fascia lata patch graft was effective in revision of trabeculectomy.

Bringing home the mission of the Fourth World Conference on Women

The objective of the Public Initiative of The American Dietetic Association's 1996-1999 Strategic Framework (see page 559 of this issue for details) is to influence the public's access to sound, scientifically based nutrition information. One way the ADA is promoting this objective is by identifying and targeting the nutrition needs and concerns of specific populations. In June 1993, the ADA became a major player in the effort to improve the health of America's women by launching the Nutrition & Health Campaign for Women. To target the nutrition needs of women most effectively, information about how women live is fundamental.

Inwardly rectifying K+ currents in isolated human retinal pigment epithelial cells

PURPOSE

K+ channels in the retinal pigment epithelium (RPE) play a number of important roles, including the establishment of membrane potential, the transport of K+ between the subretinal space and choroid, and the generation of the c-wave of the electroretinogram. Previous studies on amphibian RPE demonstrated that these functions are likely served by an inwardly rectifying K+ channel. The aim of this study was to characterize inwardly rectifying K+ channels in cultured and freshly isolated adult human RPE (hRPE) cells.

METHODS

Single cells were dispersed enzymatically from primary cultures of adult hRPE or from fresh adult hRPE-choroid. Ionic currents were recorded using either the perforated-patch or whole-cell configuration of the patch-clamp technique.

RESULTS

In 5 mM external K+, roughly 20% of cultured hRPE cells exhibited a strong inwardly rectifying K+ conductance that passed inward but little outward current. This conductance increased when [K+]o was increased and exhibited a voltage-dependent block by external Na+ at negative potentials. In contrast, all freshly isolated hRPE cells exhibited a mild inwardly rectifying K+ conductance that mediated substantial outward current at physiological voltages. This conductance decreased when [K+]o was increased and showed no voltage-dependent block by external Na+.

CONCLUSION

The authors conclude that fresh hRPE cells express a mild inwardly rectifying K+ conductance. The operation of this conductance at physiological voltages makes it a likely candidate for the resting K+ conductances of the apical and basolateral membranes. Cultured hRPE cells express a functionally different channel type that may reflect a change in phenotype.

Adjunctive subconjunctival mitomycin C in glaucoma triple procedure

PURPOSE

To evaluate the potential benefit of adjunctive subconjunctival mitomycin in patients with primary open-angle glaucoma undergoing primary trabeculectomy combined with phacoemulsification and intraocular lens implantation.

METHODS

Seventy-eight eyes of 78 patients with primary open-angle glaucoma with visually symptomatic cataracts and no previous incisional surgery were randomized to receive either no mitomycin C or a subconjunctival application of 1-, 3-, or 5-minute mitomycin C (0.5 mg/ml).

RESULTS

Follow-up (mean +/- standard deviation) was 21.0 +/- 7.7 months. The mean postoperative intraocular pressures were significantly lower with significantly less medications than the preoperative values at each follow-up time (1, 3, 6, 9, 12, 15 months, and last follow-up) for all groups (P < 0.05 for each). However, there was no significant difference at each follow-up time in intraocular pressure, medications, or best-corrected visual acuity among the four groups or between the control and the total mitomycin C group.

CONCLUSION

Adjunctive subconjunctival mitomycin C did not further improve the final intraocular pressure outcome of the primary trabeculectomy combined with phacoemulsification and intraocular lens implantation in patients with primary open-angle glaucoma. Future studies will determine the appropriate role, if any, for adjunctive mitomycin C in selected primary glaucoma triple procedures.

An outwardly rectifying K+ current active near resting potential in human retinal pigment epithelial cells

Currents in freshly dissociated adult human retinal pigment epithelial (RPE) cells were studied using the perforated patch-clamp technique. The zero-current potential (V0) averaged -48.9 +/- 7.7 mV (n = 50). Depolarizing voltage pulses from -70 mV evoked an outward current that activated with first-order kinetics and that did not inactivate during prolonged depolarizations. Repolarizing the membrane potential produced tail currents that reversed near the K+ equilibrium potential, indicating that the sustained outward current was carried mainly by K+. The outwardly rectifying K+ conductance (gK) had an activation threshold voltage near -60 mV and was half-maximal at -37 mV. Approximately 25% of gK was active at the average V0. The K+ current was nearly completely blocked by 2 mM Ba2+ but was relatively insensitive to 20 mM tetraethylammonium. The kinetics, voltage dependence, and blocker sensitivity of this current clearly distinguish it from delayed rectifier K+ currents previously identified in RPE cells. We conclude that the sustained outward K+ current may help establish the resting potential of the apical and/or basolateral membranes and may also participate in K+ transport across the RPE.

Effects of Ba2+ and Cs+ on apical membrane K+ conductance in toad retinal pigment epithelium

Intracellular microelectrode techniques were employed to characterize the blocker sensitivity of the K+ conductance (gK) at the apical membrane of the toad retinal pigment epithelium (RPE). Increasing the K+ concentration in the apical bath ([K+]o) from 2 to 5 mM produced a rapid depolarization of the apical membrane potential (VA). The addition of 0.5 mM Ba2+ or 5 mM Cs+ to the apical bath rapidly depolarized VA and increased the transepithelial resistance and ratio of apical-to-basolateral membrane resistance. In the presence of apical Ba2+ or Cs+, the response of VA to delta [K+]o was markedly reduced, indicating that these ions are effective blockers of apical gK. The Ba(2+)- and Cs(+)-induced decreases in the apparent apical-to-basolateral membrane conductance ratio were concentration dependent, with apparent dissociation constants of 17 microM and 0.5 mM, respectively. The apparent blocker sensitivity of apical gK is similar to that previously demonstrated for the inwardly rectifying K+ conductance in isolated toad RPE cells, suggesting that the inwardly rectifying K+ conductance comprises much of apical gK.

Membrane polarity of the Na(+)-K+ pump in primary cultures of Xenopus retinal pigment epithelium

The retinal pigment epithelium is a transporting epithelium that helps regulate the volume and composition of the subretinal space surrounding photoreceptor outer segments. The capacity of the RPE to actively transport Na+ and K+ between the retina and the blood supply depends on the localization of the Na+, K(+)-ATPase to the apical membrane, but in culture this polar distribution can be lost. Using primary cultures of Xenopus RPE, we examined the anatomical and functional polarity of this electrogenic pump. Confluent monolayers were established on Matrigel-coated microporous filters and cultured for 2-4 weeks in serum-free defined medium. Electrogenic pump activity at the apical and basolateral membranes was assayed by mounting the monolayer and filter in an Ussing chamber and exposing one or the other surface to ouabain while recording the apical (Vap) and basolateral (Vba) membrane potentials with an intracellular microelectrode. The addition of 0.2 mM ouabain to the apical bath caused Vap to rapidly depolarize by about 4 mV, consistent with the inhibition of a hyperpolarizing pump current at that membrane. When ouabain was added to the basal bath, however, it had no effect on Vba, suggesting the absence of a functional Na(+)-K+ pump on the basolateral membrane. To confirm these electrophysiological results, we examined the distribution of the Na+, K(+)-ATPase catalytic component using an antiserum specific for the bovine kidney alpha subunit. Antibody labeling of cultures was highly polarized, with strong reaction present on the apical microvilli, but not the basolateral cell surfaces. The findings of this study indicate that the Na(+)-K+ pump in monolayers of Xenopus RPE, as in native RPE, is located mainly in the apical membrane, providing evidence of a functionally intact transport pathway in these primary cultures.

Exogenous endophthalmitis initially treated without systemic antibiotics

PURPOSE

In 1987, the authors reported the successful eradication of infection in 16 patients with culture-proven acute exogenous bacterial endophthalmitis using intravitreal but no systemic antibiotics. They retrospectively reviewed additional consecutive cases since then to determine if the initial omission of systemic antibiotics remained reasonable.

METHODS

Twenty patients had culture-proven endophthalmitis. Four patients initially received systemic antibiotics for orbital cellulitis (2 patients), prevention of a possible scleral buckle infection (1 patient), and ascending cholangitis (1 patient). The remaining 16 patients were treated initially with intravitreal antibiotics only.

FINDINGS

Three of these additional 16 patients ultimately required systemic antibiotics for orbital cellulitis (1 patient), infectious scleritis (1 patient), and prevention of central nervous system infection with Neisseria meningitidis (1 patient). Only in one patient who had a neglected endophthalmitis and in whom an orbital cellulitis ultimately developed were we unable to clear the intraocular infection. In the overall series of 32 patients, cultures yielded staphylococcal species in 16 eyes, gram-positive bacilli in 3, streptococcal infection in 5, gram-negative cocci in 1, and gram-negative bacilli in 7. Half of the 14 specimens (1 aqueous and 13 vitreal) collected at the time of 16 reinjections in 13 eyes yielded organisms. Half (16/32) of the eyes attained visual acuity of 20/40 or better; 87.5% (28/32) attained visual acuity of 20/400 or better.

CONCLUSIONS

Therapy with intravitreal antibiotics without systemic antibiotics is reasonable, unless the infection has extended (or is at risk to extend) beyond the globe. Such evidence includes an elevated temperature or leukocyte count, corneal ring abscess, proptosis, loss of extraocular movements, scleral abscesses or infectious scleritis, and, perhaps, the presence of a scleral buckle.

Properties of the inwardly rectifying K+ conductance in the toad retinal pigment epithelium

An inwardly rectifying K+ current was analysed in isolated toad retinal pigment epithelial (RPE) cells using the perforated-patch clamp technique. The zero-current potential (Vo) of RPE cells averaged -71 mV when the extracellular K+ concentration ([K+]o) was 2 mM. Increasing [K+]o from 0.5 to 5 mM shifted V0 by +43 mV, indicating a relative K+ conductance (TK) of 0.74. At [K+]o greater than 5 mM, TK decreased to 0.53. Currents were larger in response to hyperpolarizing voltage pulses than depolarizing pulses, indicating an inwardly rectifying conductance. Currents were time independent except in response to voltage pulses to potentials positive to 0 mV, where the outward current decayed with an exponential time course. Both the inwardly rectifying current and the transient outward current were eliminated by the addition of 0.5 mM Ba2+, 5 mM Cs+ or 2 mM Rb+ to the extracellular solution. The current blocked by these ions reversed near the K+ equilibrium potential (EK) over a wide range of [K+]o, indicating a highly selective K+ channel. The current-voltage relationship of the isolated K+ current exhibited mild inward rectification at voltages negative to -20 mV and a negative slope conductance at voltages positive to -20 mV. The Cs(+)- and Ba(2+)-induced blocks of the K+ current were concentration dependent but voltage independent. The apparent dissociation constants were 0.8 mM for Cs+ and 40 microM for Ba2+. The K+ conductance decreased when extracellular Na+ was removed. Increasing [K+]o decreased the K+ chord conductance (gK) at negative membrane potentials. In the physiological voltage range, increasing [K+]o from 2 to 5 mM caused gK to decrease by approximately 25%. We conclude that the inwardly rectifying K+ conductance represents the resting K+ conductance of the toad RPE apical membrane. The unusual properties of this conductance may enhance the ability of the RPE to buffer [K+]o changes that take place in the subretinal space at the transition between dark and light.

cAMP-activated chloride currents in amphibian retinal pigment epithelial cells

1. The effect of cAMP on whole-cell currents in isolated retinal pigment epithelial (RPE) cells of the bullfrog and marine toad was investigated by means of the perforated patch clamp technique. 2. Superfusing cells with either cAMP or forskolin led to the development of a time-independent current that had a linear current-voltage (I-V) relationship. The reversal potential of (Vrev) of the cAMP-activated current was unaffected by the removal of either Na+ or HCO3- from the external and internal solutions or by the addition of extracellular barium, but it was near the Cl- equilibrium potential (ECl) over a wide range of extracellular Cl- concentrations, suggesting the presence of a Cl(-)-selective channel. 3. The anion permeability sequence of the cAMP-activated conductance calculated from biionic reversal potentials was NO3- = I- > Br- > Cl- >> HCO3- > methanesulphonate. 4. The conductance was blocked by a variety of Cl- transport inhibitors, including 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS), 4,4'-dinitro-2,2'- stilbene disulphonic acid (DNDS), frusemide, N-phenylanthranilic acid (DPC) and niflumic acid. 5. The present study demonstrates that cAMP activates a Cl(-)-selective channel that most probably resides in the basolateral membrane.

Herpes zoster-associated meningoencephalitis in patients with systemic cancer

We reviewed the experience at the Mayo Clinic with neurologic complications related to herpes zoster in patients with systemic cancer. Aside from pain, the most common neurologic complication was zoster-associated meningoencephalitis, which occurred in 9 of 1,125 patients. In these nine patients, the most common underlying malignant lesions were chronic lymphocytic leukemia and lymphoma. All patients in whom meningoencephalitis developed had trigeminal zoster or disseminated zoster. The primary neurologic symptoms were headache, confusion, and somnolence. Nuchal rigidity and fever were uncommon. The response to treatment with acyclovir was generally favorable.

Direct evidence for a basolateral membrane Cl- conductance in toad retinal pigment epithelium

There is now evidence that a Cl- conductance on the basal membrane of the retinal pigment epithelium (RPE) is involved in the generation of both the fast oscillation and the light peak of the direct-current electroretinogram as well as being critical for transepithelial fluid and salt movement. In the present study, we characterized the basolateral membrane Cl- conductance of an in vitro preparation of toad RPE-choroid using conventional and Cl(-)-selective microelectrodes. Under control conditions, the potential across the apical (Vap) and basal (Vba) membranes averaged -60 +/- 2 and -45 +/- 2 mV, respectively (n = 40). Intracellular Cl- activity (aiCl = 20 +/- 1 mM) was distributed above equilibrium across both membranes, consistent with active accumulation of Cl-. A sixfold decrease in Cl- in the basal bath depolarized Vba by 12 +/- 1 mV (n = 17) and increased the apparent basal membrane resistance. By sequential measurement of aiCl and subepithelial Cl- activity during a step decrease in basal Cl-, we constructed the change in Cl- equilibrium potential (ECl) across the basal membrane. Estimation of the change in basal membrane electromotive force during the change in ECl gave an average value for the Cl- transference number (TCl) of 0.45. Further evidence for a Cl- conductance was obtained by measuring changes in aiCl induced by transepithelial current. Depolarizing Vba elevated aiCl, whereas hyperpolarizing Vba had the opposite effect, consistent with conductive Cl- movement across the basal membrane. Both the amplitude of the Cl- diffusion potential and the current-induced changes in aiCl were reduced by basal perfusion with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (250-500 microM), a blocker of Cl- channels in some epithelia.

Effects of current clamp on chick retinal pigment epithelium

The basal membrane of the retinal pigment epithelium (RPE) is the origin of two components of the electroretinogram, the fast oscillation and the light peak. Both of these responses originate from changes in basal membrane potential (Vba), and both are associated with changes in basal membrane resistance (Rba). In addition, many experimental manipulations that alter Vba also produce apparent changes in Rba. These findings raise the possibility that the basal membrane contains a voltage-sensitive conductance that operates in the physiologic range and is involved causally in light-evoked and other responses. We report the results of current clamp experiments on the isolated retina-RPE-choroid of chick that were designed to test for the presence of such a voltage-sensitive conductance in the basal membrane. Depolarizing Vba by 15 mV with retina-to-choroid current had essentially no effect on either the ratio of membrane resistances (Rap/Rba) or the transtissue resistance (RTotal), indicating no alteration in Rba. In contrast, hyperpolarizing Vba by 15 mV with choroid-to-retina current caused a gradual decrease in RTotal and increase in Rap/Rba. Analysis of accompanying changes in membrane voltages and changes in intracellular c-wave amplitude suggested that the most likely cause of the decrease in RTotal is a decrease in paracellular resistance. Voltage-sensitive conductances of the basal membrane appear to play little or no role in the resistance changes that accompany changes in Vba in the physiologic range. The conductance changes underlying the fast oscillation and light peak probably result from either the modulation of channels by second messengers or changes in intracellular ion concentration.

Investigation of the effects of beta-2 stimulation on free fatty acids in man

In this study we present evidence that lipolysis in man is under beta-2 adrenergic control and that beta-2 stimulation produces a characteristic profile of individual free fatty acid (FFA) release. Twelve healthy volunteers received infusions of placebo (N Saline), terbutaline (a selective beta-2 agonist) and dilevalol (a new non-selective beta-blocker with beta-2 agonist activity). Plasma FFA concentrations during and after the infusions were measured using gas chromatography. A significant rise in total and individual FFAs was seen after 30 min of terbutaline infusion. This was most marked for oleic acid. Total and individual FFA concentrations also rose after 30 min of dilevalol infusion; this was only significant for oleic acid and was approximately 15% of the rise induced by terbutaline infusion. Placebo infusion did not cause any significant changes in FFA levels.

Voltage-dependent currents in isolated cells of the frog retinal pigment epithelium

1. Retinal pigment epithelial (RPE) cells were isolated enzymatically from bullfrog retinae. The patch-clamp technique was employed to investigate whole-cell currents under voltage-clamp conditions. 2. Isolated RPE cells were columnar or cuboidal in form, often with long processes protruding from the apical surface. Distinct apical and basal membrane domains were maintained for several hours following isolation. 3. The mean membrane capacitance was 62 pF. The resting potential averaged -30 mV, but it was as high as -75 mV in some cells. 4. Three voltage-dependent currents were observed: a time-independent and inwardly rectifying current and two time-dependent outwardly rectifying currents that had distinct kinetic properties. 5. Voltage pulses from a holding potential of -70 mV to potentials ranging from -30 to -120 mV produced membrane currents that were essentially time independent. The I-V relationship in this voltage range depended on the resting potential. It was usually inwardly rectifying in cells with resting potentials negative to about -50 mV, but tended to be linear in cells with more positive potentials. Three observations strongly suggested that the inwardly rectifying current is carried by K+. First, increasing the extracellular K+ concentration [( K+]) from 2 to 112 mM shifted the zero-current potential of the I-V relationship in the positive direction from an average value of -60 mV to 0 mV. Second, the addition of the K+ channel blockers Ba2+ (2 mM) or Cs+ (5 mM) to the extracellular solution inhibited a major component of the inwardly rectifying current. Finally, the reversal potential (Vr) of the Ba2(+)-sensitive current averaged -90 mV, near the K+ equilibrium potential (EK). 6. In approximately 50% of the cells, depolarizing voltage pulses to potentials more negative than -30 mV evoked an outward current that resembled the delayed rectifier present in other non-excitable cells. It activated with sigmoidal kinetics in less than 100 ms following a brief delay and then declined exponentially with a time constant of approximately 1 s. The peak chord conductance associated with this current was half-maximal at +14 mV. Several observations indicated that this outwardly rectifying current is carried primarily by K+: its Vr closely matched EK over a wide range of extracellular [K+]; it was inhibited 80% by exposure to the K+ channel blockers 4-aminopyridine (1 mM) and tetraethylammonium (20 mM); and it was abolished by intracellular dialysis with a K(+)-free solution.(ABSTRACT TRUNCATED AT 400 WORDS)

Investigation of the beta 2-agonist properties of dilevalol: metabolic effects of intravenous infusion

We describe two studies which investigate the beta 2-agonist properties of dilevalol. We have previously demonstrated, by giving an infusion of terbutaline to human volunteers, that beta 2-stimulation causes a rise in plasma glucose and a fall in plasma potassium. These metabolic effects can be prevented by prior beta-blockade. We now show that infusion of dilevalol produces similar, but quantitatively smaller, metabolic effects at a dose which also produces clinically significant beta-blockade, as judged by a fall in exercise heart rate. This adds support to the claim that dilevalol is a non-selective beta-blocker with selective beta 2-agonist activity.

Apical electrogenic NaHCO3 cotransport. A mechanism for HCO3 absorption across the retinal pigment epithelium

Intracellular microelectrode techniques and intracellular pH (pHi) measurements using the fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) were employed to characterize an electrogenic bicarbonate transport mechanism at the apical membrane of the frog retinal pigment epithelium (RPE). Reductions in apical concentrations of both [HCO3]o (at constant Pco2 or pHo) or [Na]o caused rapid depolarization of the apical membrane potential (Vap). Both of these voltage responses were inhibited when the concentration of the other ion was reduced or when 1 mM diisothiocyano-2-2 disulfonic acid stilbene (DIDS) was present in the apical bath. Reductions in apical [HCO3]o or [Na]o also produced a rapid acidification of the cell interior that was inhibited by apical DIDS. Elevating pHi at constant Pco2 (and consequently [HCO3]i) by the addition of apical NH4 (20 mM) produced an immediate depolarization of Vap. This response was much smaller when either apical [HCO3]o or [Na]o was reduced or when DIDS was added apically. These results strongly suggest the presence of an electrogenic NaHCO3 cotransporter at the apical membrane. Apical DIDS rapidly depolarized Vap by 2-3 mV and decreased pHi (and [HCO3]i), indicating that the transporter moves NaHCO3 and net negative charge into the cell. The voltage dependence of the transporter was assessed by altering Vap with transepithelial current and then measuring the DIDS-induced change in Vap. Depolarization of Vap increased the magnitude of the DIDS-induced depolarization, whereas hyperpolarization decreased it. Hyperpolarizing Vap beyond -114 mV caused the DIDS-induced voltage change to reverse direction. Based on this reversal potential, we calculate that the stoichiometry of the transporter is 1.6-2.4 (HCO3/Na).

cAMP stimulates the Na+-K+ pump in frog retinal pigment epithelium

Adenosine 3', 5'-cyclic monophosphate (cAMP) induced increases in active Na+ secretion and K+ absorption that were blocked by apical ouabain (10(-4) M), suggesting stimulation of the Na+-K+ pump. cAMP also produced rapid membrane voltage and resistance changes that could be divided chronologically into three phases. In phase 1, the basolateral membrane depolarized at a faster rate than the apical membrane, probably as a result of an increase in basolateral membrane conductance. In phase 2, the apical membrane repolarized toward control faster than the basal membrane, whereas in phase 3 the basolateral membrane repolarized faster than the apical membrane. Apical ouabain completely inhibited the cAMP-induced repolarization of the apical membrane during phase 2. Thus the stimulation of the Na+-K+ pump occurs within minutes of cAMP elevation. Na+ removal from the basal side did not block the cAMP-induced voltage changes, indicating that the initial conductance increase is not due to Na+. In contrast, Na+ removal from the apical bath inhibited all phases of the cAMP response. This suggests that apical membrane Na+-dependent transport mechanisms mediate the stimulation of the Na+-K+ pump. cAMP also caused a significant drop in intracellular K+ activity (approximately 5 mM) that preceded phase 2. This drop could stimulate the Na+-K+ pump, as suggested by previous experiments.

Adenylate cyclase stimulation alters transport in frog retinal pigment epithelium

The effect of adenylate cyclase inhibitors and activators on enzyme kinetics and cyclic AMP (cAMP) levels was determined in the bullfrog retinal pigment epithelium (RPE). The RPE enzyme has two Km for ATP: 5.2 X 10(-4) and 4.0 X 10(-5) M, with Vmax of 2.5 and 0.25 nmol X mg protein-1 X min-1. Forskolin, the most potent activator, produced a fourfold increase in enzyme activity and, in the presence of isobutylmethylxanthine (IBMX), an inhibitor of phosphodiesterase, caused a 20-fold increase in cAMP levels. Alloxan, a potent inhibitor, blocked the forskolin-induced activation of this enzyme. In the isolated RPE choroid, forskolin (plus IBMX) produced changes in membrane voltage and resistance that were similar in magnitude but slower in time course than those produced by exogenous cAMP. Like exogenous cAMP, forskolin also decreased steady-state fluid and solute transport in isotonic proportions. Therefore, modulation of RPE adenylate cyclase activity plays an important role in the control of RPE transport.

Effects of cyclic AMP on fluid absorption and ion transport across frog retinal pigment epithelium. Measurements in the open-circuit state

A modified version of a capacitance probe technique has been used to measure fluid transport across the isolated retinal pigment epithelium (RPE)-choroid of the bullfrog. The accuracy of this measurement is 0.5-1.0 nl/min. Experiments carried out in the absence of external osmotic or hydrostatic gradients show that the RPE-choroid transports fluid from the retinal to the choroid side of the tissue at a rate of approximately 10 nl/min (4-6 microliters/cm2 X h). Net fluid absorption (Jv) was abolished within 10 min by the mitochondrial uncoupler 2,4-dinitrophenol. It was also inhibited (70%) by the removal of bicarbonate from the bulk solutions bathing the tissue. Ouabain caused a slow decrease in Jv (no effect at 10 min, 70% at 3 h), which indicates that RPE fluid transport is not directly coupled to the activity of the Na-K pump located at the apical membrane of this epithelium. In contrast to ouabain, cyclic AMP (cAMP) produced a quick decrease in Jv (84% within 5 min). Radioisotope experiments in the open circuit show that cAMP stimulated secretory fluxes of Na and Cl, which accounted for the observed cAMP-induced decrease in Jv. The direction of net fluid absorption, the magnitudes of the net ionic fluxes in the open circuit, and the dependence of Jv on external bicarbonate concentration strongly suggest that fluid absorption is generated primarily by the active absorption of bicarbonate.

Regeneration of beta-adrenergic receptors in senescent rats: a study using an irreversible binding antagonist

The drug used in this study, bromoacetylalprenololmenthane, has the ability to bind and block irreversibly beta-adrenergic receptors. The drug was bound to membranes prepared from hearts, lungs, and brains of both senescent and young rats with a similar affinity. When this drug was injected into rats in nontoxic doses (up to 70 mg/kg), up to 90% of beta-adrenergic receptors were irreversibly blocked 4 hr after injection, whereas the injection of similar amounts of (+/-)-alprenolol was without effect on receptor number. In senescent animals this blockade lasted considerably longer than in young animals; receptor numbers in hearts and lungs of senescent rats returned to control levels only 1 month after injection. The number of beta-adrenergic receptors in brains of senescent rats was unaffected by this drug. Thus, based upon the long-lasting blockade of beta-adrenergic receptors in therapeutically important organs, it appears that irreversible binding blockers may have potential in the treatments of senescent organisms.