Safety of primary nasotracheal intubation in the pediatric intensive care unit (PICU)

Background

Nasal tracheal intubation (TI) represents a minority of all TI in the pediatric intensive care unit (PICU). The risks and benefits of nasal TI are not well quantified. As such, safety and descriptive data regarding this practice are warranted.

Methods

We evaluated the association between TI route and safety outcomes in a prospectively collected quality improvement database (National Emergency Airway Registry for Children: NEAR4KIDS) from 2013 to 2020. The primary outcome was severe desaturation (SpO2 > 20% from baseline) and/or severe adverse TI-associated events (TIAEs), using NEAR4KIDS definitions. To balance patient, provider, and practice covariates, we utilized propensity score (PS) matching to compare the outcomes of nasal vs. oral TI.

Results

A total of 22,741 TIs [nasal 870 (3.8%), oral 21,871 (96.2%)] were reported from 60 PICUs. Infants were represented in higher proportion in the nasal TI than the oral TI (75.9%, vs 46.2%), as well as children with cardiac conditions (46.9% vs. 14.4%), both p < 0.001. Severe desaturation or severe TIAE occurred in 23.7% of nasal and 22.5% of oral TI (non-adjusted p = 0.408). With PS matching, the prevalence of severe desaturation and or severe adverse TIAEs was 23.6% of nasal vs. 19.8% of oral TI (absolute difference 3.8%, 95% confidence interval (CI): - 0.07, 7.7%), p = 0.055. First attempt success rate was 72.1% of nasal TI versus 69.2% of oral TI, p = 0.072. With PS matching, the success rate was not different between two groups (nasal 72.2% vs. oral 71.5%, p = 0.759).

Conclusion

In this large international prospective cohort study, the risk of severe peri-intubation complications was not significantly higher. Nasal TI is used in a minority of TI in PICUs, with substantial differences in patient, provider, and practice compared to oral TI.A prospective multicenter trial may be warranted to address the potential selection bias and to confirm the safety of nasal TI.

Adverse Tracheal Intubation Events in Critically Ill Underweight and Obese Children: Retrospective Study of the National Emergency Airway for Children Registry (2013-2020)

OBJECTIVES

Extremes of patient body mass index are associated with difficult intubation and increased morbidity in adults. We aimed to determine the association between being underweight or obese with adverse airway outcomes, including adverse tracheal intubation (TI)-associated events (TIAEs) and/or severe peri-intubation hypoxemia (pulse oximetry oxygen saturation < 80%) in critically ill children.

DESIGN/SETTING

Retrospective cohort using the National Emergency Airway for Children registry dataset of 2013-2020.

PATIENTS

Critically ill children, 0 to 17 years old, undergoing TI in PICUs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Registry data from 24,342 patients who underwent TI between 2013 and 2020 were analyzed. Patients were categorized using the Centers for Disease Control and Prevention weight-for-age chart: normal weight (5th-84th percentile) 57.1%, underweight (< 5th percentile) 27.5%, overweight (85th to < 95th percentile) 7.2%, and obese (≥ 95th percentile) 8.2%. Underweight was most common in infants (34%); obesity was most common in children older than 8 years old (15.1%). Underweight patients more often had oxygenation and ventilation failure (34.0%, 36.2%, respectively) as the indication for TI and a history of difficult airway (16.7%). Apneic oxygenation was used more often in overweight and obese patients (19.1%, 19.6%) than in underweight or normal weight patients (14.1%, 17.1%; p < 0.001). TIAEs and/or hypoxemia occurred more often in underweight (27.1%) and obese (24.3%) patients ( p < 0.001). TI in underweight children was associated with greater odds of adverse airway outcome compared with normal weight children after adjusting for potential confounders (underweight: adjusted odds ratio [aOR], 1.09; 95% CI, 1.01-1.18; p = 0.016). Both underweight and obesity were associated with hypoxemia after adjusting for covariates and site clustering (underweight: aOR, 1.11; 95% CI, 1.02-1.21; p = 0.01 and obesity: aOR, 1.22; 95% CI, 1.07-1.39; p = 0.002).

CONCLUSIONS

In underweight and obese children compared with normal weight children, procedures around the timing of TI are associated with greater odds of adverse airway events.

Tracheal Intubation by Advanced Practice Registered Nurses in Pediatric Critical Care: Retrospective Study From the National Emergency Airway for Children Registry (2015-2019)

OBJECTIVES

To describe tracheal intubation (TI) practice by Advanced Practice Registered Nurses (APRNs) in North American PICUs, including rates of TI-associated events (TIAEs) from 2015 to 2019.

DESIGN/SETTING

Retrospective study using the National Emergency Airway Registry for Children with all TIs performed in PICU and pediatric cardiac ICU between January 2015 and December 2019. The primary outcome was first attempt TI success rate. Secondary outcomes were TIAEs, severe TIAEs, and hypoxemia.

SUBJECTS

Critically ill children requiring TI in a PICU or pediatric cardiac ICU.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Among 11,012 TIs, APRNs performed 1,626 (14.7%). Overall, TI by APRNs, compared with other clinicians, occurred less frequently in patients with known difficult airway (11.1% vs. 14.3%; p < 0.001), but more frequently in infants younger than 1 year old (55.9% vs. 44.4%; p < 0.0001), and in patients with cardiac disease (26.3% vs. 15.9%; p < 0.0001).There was lower odds of success in first attempt TI for APRNs vs. other clinicians (adjusted odds ratio, 0.70; 95% CI, 0.62-0.79). We failed to identify a difference in rates of TIAE, severe TIAE, and oxygen desaturation events for TIs by APRNs compared with other clinicians. The TI first attempt success rate improved with APRN experience (< 1 yr: 54.2%, 1-5 yr: 59.4%, 6-10 yr: 67.6%, > 10 yr: 63.1%; p = 0.021).

CONCLUSIONS

TI performed by APRNs was associated with lower odds of first attempt success when compared with other ICU clinicians although there was no appreciable difference in procedural adverse events. There appears to be a positive relationship between experience and success rates. These data suggest there is an ongoing need for opportunities to build on TI competency with APRNs.

Development of a paediatric airway management checklist for the emergency department: a modified Delphi approach

BACKGROUND

Airway management checklists have improved paediatric patient safety in some clinical settings, but consensus on the appropriate components to include on a checklist for paediatric tracheal intubation in the ED is lacking.

METHODS

A multidisciplinary panel of 14 experts in airway management within and outside of paediatric emergency medicine participated in a modified Delphi approach to develop consensus on the appropriate components for a paediatric airway management checklist for the ED. Panel members reviewed, modified and added to the components from the National Emergency Airway Registry for Children airway safety checklist for paediatric intensive care units using a 9-point appropriateness scale. Components with a median score of 7.0-9.0 and a 25th percentile score ≥7.0 achieved consensus for inclusion. A priori, the modified Delphi method was limited to a maximum of two rounds for consensus on essential components and one additional round for checklist creation.

RESULTS

All experts participated in both rounds. Consensus was achieved on 22 components. Twelve were original candidate items and 10 were newly suggested or modified items. Consensus components included the following categories: patient assessment and plan (5 items), patient preparation (5 items), pharmacy (2 items), equipment (7 items) and personnel (3 items). The components were formatted into a 17-item clinically usable checklist.

CONCLUSIONS

Using the modified Delphi method, consensus was established among airway management experts around essential components for an airway management checklist intended for paediatric tracheal intubation in the ED.

Protein biomarkers for incident deep venous thrombosis in critically ill adolescents: An exploratory study

BACKGROUND

There are no tests to identify critically ill children at high risk of deep venous thrombosis (DVT). In this exploratory study, we aimed to identify proteins that are associated with incident DVT in critically ill adolescents.

PROCEDURE

Plasma samples were obtained from critically ill adolescents within 24 hours after initiation of cardiopulmonary support. The adolescents were followed with ultrasound to detect the development of DVT of the lower extremity and clinically for bleeding. Thrombin-antithrombin complex and prothrombin fragment 1+2 were measured using immunosorbent assays, whereas procoagulation and anticoagulation factors were measured using multiplex assays. Plasma samples were also analyzed using SOMAscan, an aptamer-based capture assay. The associations between DVT and the log-transformed level of the proteins were assessed using logistic regression adjusting for the presence of femoral venous catheter and severity of illness. Associations were expressed as odds ratio (OR) for every log-fold increase in level of the protein with 95% confidence interval (CI).

RESULTS

Plasma from 59 critically ill adolescents, of whom 9 developed incident DVT, was analyzed. The median age of the adolescents was 15.1 years (interquartile range, 14.0-16.7 years). Higher levels of thrombin-antithrombin complex (OR: 31.54; 95% CI: 2.09-475.92) and lower levels of factor XIII (OR: 0.03; 95% CI: 0.002-0.44) were associated with DVT. CD36, MIC-1, and EpoR were marginally associated with DVT. Only factor XIII was associated with clinically relevant bleeding (OR: 0.27; 95% CI: 0.08-0.97).

CONCLUSIONS

We identified candidate protein biomarkers for incident DVT. We plan to validate our findings in adequately powered studies.

Epidemiology of Lower Extremity Deep Venous Thrombosis in Critically Ill Adolescents

OBJECTIVE

To determine the epidemiology of lower extremity deep venous thrombosis (DVT) in critically ill adolescents, which currently is unclear.

STUDY DESIGN

We performed a multicenter, prospective, cohort study. Adolescents aged 13-17 years who were admitted to 6 pediatric intensive care units and were anticipated to receive cardiopulmonary support for at least 48 hours were eligible, unless they were admitted with DVT or pulmonary embolism or were receiving or anticipated to receive therapeutic anticoagulation. While patients were in the unit, serial sonograms of the lower extremities were performed, then centrally adjudicated. Bayesian statistics were used to leverage the similarities between adults and adolescents.

RESULTS

A total of 88 adolescents were enrolled, from whom 184 lower extremity sonograms were performed. Of these, 9 adolescents developed DVT, with 1 having bilateral DVT. The frequency of DVT was 12.4% (95% credible interval: 6.1%, 20.1%), which ranged from 6.3% to 19.8% with a variability of 41.0% across units. All cases of DVT occurred in adolescents who received invasive mechanical ventilation (frequency: 16.5%; 95% credible interval 8.1%, 26.6%). DVT was associated with femoral central venous catheterization (OR 15.44; 95% credible interval 1.62, 69.05) and severe illness (OR for every 0.1 increase in risk of mortality 3.11; 95% credible interval 1.19, 6.85). DVT appears to be associated with prolonged days on support.

CONCLUSIONS

Our findings highlight the similarities and differences in the epidemiology of DVT between adults and adolescents. They support the conduct and inform the design of a trial of pharmacologic prophylaxis in critically ill adolescents.

Diagnostic accuracy of point-of-care ultrasound for catheter-related thrombosis in children

BACKGROUND

Compared with consultative US performed by the radiology department, point-of-care US performed by non-radiology physicians can accurately diagnose deep venous thrombosis in adults.

OBJECTIVE

In preparation for a multicenter randomized controlled trial, we determined the accuracy of point-of-care US in diagnosing central venous catheter-related thrombosis in critically ill children.

MATERIALS AND METHODS

Children <18 years old with a central venous catheter who were admitted to the intensive care unit were enrolled. Consultative and point-of-care compression ultrasounds with Doppler were done on the vein where the catheter was inserted within 24 h after insertion. Repeat US was obtained within 24 h of removal of the catheter. All images were centrally, blindly and independently adjudicated for thrombosis by a team of pediatric radiologists. Chance-corrected agreement between readings was calculated.

RESULTS

From 84 children, 152 pairs of consultative and point-of-care ultrasounds were analyzed. A total of 38 (25.0%) consultative and 17 (11.2%) point-of-care ultrasounds were positive for thrombosis. The chance-corrected agreement between consultative and point-of-care ultrasounds was 0.17 (standard error: 0.07; P = 0.008). With consultative US as a reference, the sensitivity of point-of-care US was 28.1% (95% confidence interval: 13.7%-46.7%) with a specificity of 91.8% (95% confidence interval: 84.4%-96.4%). A catheter in the subclavian vein was associated with discordant readings (adjusted odds ratio: 4.00; 95% confidence interval: 1.45-13.94).

CONCLUSION

Point-of-care US, when performed by non-radiology physicians and centrally adjudicated by pediatric radiologists in the setting of a multicenter randomized controlled trial, may not accurately diagnose catheter-related thrombosis in critically ill children.

Characteristics and outcomes of pediatric rapid response teams before and after mandatory triggering by an elevated Pediatric Early Warning System (PEWS) score

BACKGROUND

The Pediatric Early Warning System (PEWS) was created to identify unstable patients before their deterioration. Rapid response teams (RRTs) were developed to assist with management of such patients. In 2009, our institution mandated the activation of RRTs if a PEWS score was elevated (ie, ≥5).

OBJECTIVES

The goal of this study was to examine changes in characteristics of RRT calls before and after the implementation of a mandatory hospital policy requiring RRT activation due to an elevated PEWS score.

METHODS

This study was a retrospective database review, with RRT data from June 2007 to December 2010 examined. A total of 44 RRTs were recorded before mandatory triggering and 69 RRTs afterward in the study period (P = .32).

RESULTS

Compared with the premandatory group, the mandatory triggering group found that tachycardia was a more frequent trigger for RRTs, with an increase of 26.1% (P = .004). RRTs triggered by a change in mental status/agitation decreased by 22.9% (P = .009). An increase of 15.1% of RRTs required no interventions with mandatory triggering. Nighttime RRTs increased by17.5% (P = .07). There was a trend toward decreased PICU transfers in the mandatory triggering group, with no significant change in code blue calls.

CONCLUSIONS

A hospital policy of mandating RRT activation based on PEWS scores increased nighttime calls and altered the primary reasons for RRT activation in our center, with no evidence of improvements in patient care. These findings should be interpreted with caution given the relatively rare outcomes the policy is intended to prevent; however, our findings highlight the difficulties inherent in evaluating methods to improve pediatric patient safety.

Is intraocular pressure in the early postoperative period predictive of antimetabolite-augmented filtration surgery success?

PURPOSE

To determine whether intraocular pressure (IOP) in the early postoperative period after trabeculectomy or combined phacoemulsification-trabeculectomy, augmented with antimetabolite, correlates with IOP at one year in surgeries considered to be successful at that time point.

DESIGN

Retrospective case series.

METHODS

A chart review of antimetabolite-augmented surgical procedures done by DJG and JBS between January 1994 and November 2000 identified 82 primary or secondary trabeculectomies and 53 combined phacoemulsification-trabeculectomies with at least one year of follow-up. The success rate for each surgical subgroup was calculated and IOP on postoperative days (POD +/- SD) 1, 7 (+/-2), 30 (+/-5), 90 (+/-10), and 180 (+/-20) was correlated with IOP at one year (POY 1, between month 12 and 15) using linear regression. IOP at each time point was compared among eyes that achieved success at one year with and without the use of IOP-lowering agents.

RESULTS

Of the 82 eyes having undergone antimetabolite-augmented trabeculectomies and the 53 eyes having undergone combined surgeries with at least one year of follow-up, the surgical success rates at POY 1 were 87.8% (72 of 82 eyes) and 92.5% (49 of 53 eyes). Of these, 42 eyes (58.3%) from 39 patients in the trabeculectomy group and 27 eyes (55.1%) from 24 patients in the combined surgery group did not require glaucoma medications at one year postsurgically, and were considered complete surgical successes. Mean preoperative IOP mm Hg +/- SD was 26.0 +/- 8.5 for the trabeculectomy group and 18.2 +/- 4.5 for the phaco-trabeculectomy group. Postoperative IOP at POD 1, POD 7, POD 30, POD 90, POD 180, and POY 1 respectively for the eyes undergoing trabeculectomy were 13.9 +/- 10.4, 9.5 +/- 6.2, 12.0 +/- 5.5, 12.0 +/- 5.2, 12.8 +/- 5.9, and 12.1 +/- 4.3, and for the combined surgery group were 20.8 +/- 12.5, 9.7 +/- 5.7, 12.2 +/- 5.4, 11.1 +/- 3.4, 11.6 +/- 4.6, and 10.3 +/- 4.3. Intraocular pressure on postoperative day one correlated poorly with intraocular pressure at POY 1 for the trabeculectomy group (R2 = 0.0788), and not at all for the combined procedures group (R2 = 0.018). The correlation was slightly better for intraocular pressure at postoperative day 90 for the trabeculectomy group (R2 = 0.546), and at postoperative day 180 for the combined group (R2 = 0.37), but still rather low. Eyes requiring glaucoma medication use at POY 1 in the trabeculectomy group had higher (P < 0.009) intraocular pressure at POD 30 and at all subsequent visits than eyes not requiring these medications. Eyes requiring glaucoma medication use at POY 1 in the phaco-trabeculectomy group had higher (P < 0.0025) intraocular pressure at POD 30, POD 180, and POY 1 than eyes not requiring these medications.

CONCLUSION

Intraocular pressure in the early postoperative period correlates very poorly with intraocular pressure one year after successful antimetabolite-augmented trabeculectomy or combined cataract extraction and trabeculectomy. Starting one month after glaucoma surgery, intraocular pressure is substantially lower in eyes that will ultimately not require the use of ocular hypotensive agents to achieve clinical success one year postoperatively.

Additivity of pilocarpine to bimatoprost in ocular hypertension and early glaucoma

PURPOSE

To determine if the intraocular pressure (IOP) effect of pilocarpine at various concentrations is additive to that of bimatoprost and to assess the tolerability of this combination.

METHODS

This was a randomized, prospective trial of patients with IOP > 21 mm Hg following appropriate medication washout. For all visits IOP was measured at 9:00 AM and 11:00 AM. Following baseline visit (#1), bimatoprost 0.03% was instilled qhs OU through visit 6. Following visits 2, 3, and 4 pilocarpine (2%, 4%, 6%) was instilled qid in one randomly selected eye. Pilocarpine was discontinued after visit 5 and bimatoprost after visit 6. Two-tailed, paired t test was used to compare treated and contralateral eyes for their IOP, IOP change, percentage IOP change from baseline, and to compare IOP in the same eye at 9:00 AM and 11:00 AM (before and after pilocarpine administration). IOPs using bimatoprost alone or in combination with various pilocarpine concentrations were compared using single variant Analysis of Variance (ANOVA).

RESULTS

Seventeen patients were enrolled and 13 patients completed the study. Bimatoprost reduced IOP 28.7% to 30.5% (P < 0.0001) from baseline to visit 2. IOPs in eyes treated with bimatoprost alone or with bimatoprost and various pilocarpine concentrations were similar (P > 0.81, ANOVA). The IOP (P > 0.17) and percentage IOP change from baseline (P > 0.10) was similar in treated and contralateral eyes with all three strengths of pilocarpine. IOP values at 9:00 AM and 11:00 AM, before and after pilocarpine administration, were similar (P > 0.22).

CONCLUSION

Bimatoprost alone reduces IOP substantially. Pilocarpine added to bimatoprost at concentrations of 2%, 4%, or 6% was neither additive nor antagonistic to the ocular hypotensive efficacy of bimatoprost.

The Effect of Laser Iridotomy on the Anterior Segment Anatomy of Patients With Plateau Iris Configuration

PURPOSE

To determine if laser iridotomy altered the anterior segment anatomy of patients with plateau iris configuration.

METHODS

Twenty eyes of 9 female and 1 male patients were imaged using an ultrasound biomicroscope within 19 weeks before and 52 weeks after laser iridotomy. Measurements obtained included the anterior chamber depth (ACD), trabecular-ciliary process distance (TCPD), iris thickness (IT), angle opening distance at 500 micrometers (AOD), iridozonular distance (IZD), and trabecular-iris angle (TIA). Comparisons of the pre- and post- iridotomy measurements were made using a two-tailed paired t test.

RESULTS

Laser iridotomy elicited no statistically significant change in ACD, TCPD, IT, AOD, or TIA. However, IZD was decreased (P < 0.05) in both eyes after laser iridotomy. Configuration of the irides was flat before and after laser iridotomies.

CONCLUSION

This study suggests that laser iridotomy did not alter anterior segment anatomy, probably because of the fixed anterior insertion of the iris and ciliary body in plateau iris configuration. The decrease in IZD distance may be the result of a small posterior movement of the iris due to a reduction in relative pupillary block, secondary to laser iridotomy. The small reduction in relative papillary block in plateau iris configuration does not alter the width of the anterior chamber angle as measured by AOD and TIA.

Beta-adrenergic inhibition of rabbit lens anterior-surface K(+) conductance

PURPOSE

To characterize the effects of cAMP-elevating stimuli on the rabbit translens electrical parameters and examine the distribution of beta adrenoceptors about the epithelial surface.

METHODS

The electrophysiological experiments encompassed the isolation of lenses within a vertically arranged, Ussing-type chamber under short-circuit conditions, an approach that allowed for measurements of short-circuit current (I(sc)) across, in separate experiments, discrete surface regions. Epithelial beta receptors were localized by immunofluorescent labeling of lens cryosections primarily exposed to a polyclonal antibody against human beta( 2)-adrenoceptors. Reverse transcription - polymerase chain reaction (RT-PCR) was used to generate cDNA (using specific primers based upon the sequence of the previously cloned human beta(2) receptor) from rabbit lens RNA extracted from mechanically sequestered anterior and equatorial epithelial cells.

RESULTS

Asymmetrical I(sc) reductions with increases in translens resistance were elicited with epinephrine, isoproterenol, terbutaline, forskolin, and a lipid-permeable cAMP analogue. Electrical changes were recorded across the anterior aspect and not observed when the above compounds were applied to solutions bathing the equatorial and posterior surfaces. Immunohistochemical observations indicated the expression of beta receptors from the anterior epithelium to the equatorial region. RT-PCR yielded cDNA of expected basepair length for the apparent fragment of the beta(2)-adrenoceptor, which exhibited a sequence homology 90% identical with its human equivalent in both the anterior and equatorial epithelia.

CONCLUSIONS

The cAMP-sensitive conductance(s) appear limited to the anterior epithelium and undetectable equatorially. The asymmetrical I(sc) responses do not seem to arise from a spatial heterogeneity in epithelial receptor expression.

Beta-adrenergic stimulation of Na(+)-K(+)-2Cl(-) cotransport activity in the rabbit lens

Experimental maneuvers known to increase cellular cAMP levels evoked a stimulation in the K(+) influx across the anterior surfaces of isolated rabbit lenses, as measured by 86Rb(+) uptake. For this, the lenses were mounted in a modified Ussing-type chamber and exposed to the radiolabel under short-circuit conditions. The enhanced, cAMP-elicited flux was attributed to the basolateral Na(+)-K(+)-2Cl(-) cotransporter given its preclusion by bumetanide, a highly selective inhibitor of this symport, and the ineffectiveness of ouabain in mitigating the stimulation. The ouabain- plus bumetanide-insensitive K(+) uptake, which is about 10% of the total influx and represents passive entry of the radiolabel, was not affected by cAMP-elevating conditions. Forskolin, an activator of adenylyl cyclase; epinephrine, a non-selective adrenergic agonist; and the beta-selective agents, isoproterenol and terbutaline, were among the drugs used to elicit the increase in bumetanide-sensitive K(+) inflow. In experiments with isoproterenol, the stimulated influx evoked by the agonist was inhibited in lenses simultaneously exposed to propranolol. Other observations included that the stimulation of bumetanide-sensitive K(+) influx with forskolin was eliminated in lenses pretreated with the protein kinase inhibitors, staurosporine or H-89. However, these drugs were ineffective in preventing the increased influx produced by calyculin A, a phosphatase inhibitor, suggesting modulation of the cotransporter by at least two independent pathways. The cAMP-generating stimuli also produced an inhibition of the short-circuit current across the lens and an increase in translens resistance. These latter effects suggest that cAMP elevation also evokes an inhibition in an epithelial conductance(s) simultaneously to the stimulation of the cotransporter. As such, this study provides the first indication for the regulation of lens transport by adrenoceptors, presumably of the beta-2 subtype.

Distribution of acetylcholine-sensitive currents around the rabbit crystalline lens

The relative distribution of acetylcholine (ACh) receptors on the surface of the isolated ocular lens of the rabbit was determined from induced changes in translens short-circuit current (I(SC)) and the translenticular resistance (R(t)) at seven delineated, parallel zones from the anterior to the posterior pole. For this, one O-ring (from among several having different diameters) was used to separate two zones in a vertically arranged Ussing-type chamber. Different O-rings separated different zone pairs. Earlier experiments from this laboratory used a conventional divided chamber, which occluded the equatorial surface, to demonstrate that anterior applications of ACh transiently decreased the I(SC) due to an intracellular Ca(2+) release and inhibition of anteriorly located K(+) channels. Measurements obtained with the newly designed zonal arrangement determined that the entire epithelial surface from its anterior-most aspect to the equatorial region responds electrically to ACh exposure, while the posterior-most region does not. Furthermore, lens-mounting positions that resulted in separation of the epithelium so that portions of its surface were present in each hemichamber resulted in inverse current changes upon bilateral ACh addition to the bathing solutions. Reductions in outward cationic current across the anterior surface into the anterior bath upon ACh treatment were accompanied by an increase in translens resistance consistent with a closure of basolateral K(+) channels. Overall, these results suggest that the posterior fiber cells may lack ACh receptors, which are clearly present in the lens epithelium that covers about two-thirds of the rabbit lens surface area, and indicate that an ACh-evoked Ca(2+) signal does not spread throughout the epithelial layer. A functional role for lens acetylcholine receptors remains to be determined.

Localization of a Na(+)-K(+)-2Cl(-) cotransporter in the rabbit lens

Earlier work from this laboratory demonstrated a bumetanide-inhibitable K(+) uptake activity in cultured bovine lens epithelial cells, but not at the anterior surfaces of intact bovine lenses isolated in an Ussing-type chamber. Presently the distribution of the bumetanide-sensitive Na(+)-K(+)-2Cl(-) cotransporter within the lens was re-examined. To complement previous results, (86)Rb(+) uptake experiments were done in a chamber design that limited exposure of the radiolabel to specific surfaces of rabbit lenses under short-circuit conditions. In addition, the cotransporter protein (NKCC1, but not NKCC2) was immune-detected in Western blots. For the latter, membrane preparations were obtained from capsule-plus-epithelial specimens, and from three cortical fractions, i.e. the anterior, equatorial, and posterior regions, as well as a fifth, nuclear fraction. K(+) influxes across the anterior-polar, equatorial, and posterior-polar surfaces were 0.375, 0.348 and 0.056 microEq (hr cm(2))(-1) respectively, rates that were not significantly reduced by the presence of 0.1 mM bumetanide (P > 0.15, as unpaired data). In contrast, bumetanide-sensitive K(+) influx rates were measured across the anterior and equatorial surfaces under hypertonic, but not under hypo-osmotic conditions. In culture, bumetanide and ouabain were equipotent in reducing by approximately half the K(+) uptake of quiescent, rabbit lens epithelial cells under control, iso-osmotic conditions, indicating a cell-culture induced up-regulation of the cotransport activity by an undetermined mechanism. The immunoblotting of lens membrane proteins elicited approximately 170-180 kDa bands accordant with the identity of the NKCC1 isoform in the epithelial and cortical equatorial fractions. Thus, NKCC1 was readily demonstrated using membrane specimens taken from within the lens. Its activity in the intact organ may be activated by conditions fostering cell shrinkage, and perhaps, agents stimulating epithelial cell elongation, given its distribution within the lens.