No-Opioid Discharge Following Artificial Urinary Sphincter Placement Does Not Significantly Increase Health Care System Burden

INTRODUCTION

Postoperative opioid prescriptions are associated with an increased risk of opioid dependance. While studies on no-opioid discharge strategies have been assessed following many urologic procedures, the effect of no-opioid discharges on health care utilization following artificial urinary sphincter placement is unknown. We performed a single-surgeon retrospective comparison of health care system interactions following artificial urinary sphincter implantation between patients who received an opioid prescription on discharge to those who did not.

METHODS

We identified 101 male patients who underwent 3-piece artificial urinary sphincter placement or revision by 1 provider between 2015 and 2022. All patients were discharged with acetaminophen and ibuprofen; none received intraoperative local anesthetic. Demographic information, preprocedural opioid use, opioid prescriptions following the procedure, postoperative office communications, unplanned office visits, and emergency department (ED) visits were recorded for each patient for 90 days.

RESULTS

Forty-five patients (45%) were discharged without an opioid prescription and 56 patients (55%) were discharged with an opioid prescription. No differences in age, race, BMI, operative time, or presence of a preoperative opioid prescription were observed. Discharge without an opioid did not significantly increase the number of office communications (55% vs 40%, P = .11), unplanned office visits (36% vs 23%, P = .19), or ED visits (20 vs 12, P = .41) within 90 days of implantation/revision.

CONCLUSIONS

Opioids can be omitted from the discharge analgesic regimen following artificial urinary sphincter placement without increasing burden to surgical office staff or local EDs. Providers should consider no-opioid discharges for patients undergoing uncomplicated sphincter placement to limit risk of opioid-related morbidity.

Minimally Invasive Management of Posterior Urethral Stricture/Stenosis with DVIU and Mitomycin C Injection

OBJECTIVE

To demonstrate a technique for minimally invasive endoscopic management of posterior urethral strictures, including those at the bladder neck and vesicourethral anastomosis.

METHODS

Herein, we have included endoscopic video footage from 3 patients with posterior urethral strictures, including 1 at the bladder neck, 1 at the vesicourethral anastomosis, and 1 in the bulbomembranous urethra. In each patient, we perform a direct visualization internal urethrotomy (DVIU) with incisions at the 5 and 7 o'clock positions to widen the urethral lumen, followed by injection of 2 mg mitomycin C (MMC) in a total volume of 5 mL sterile water.

RESULTS

Herein, we describe our technique for the endoscopic management of posterior urethral strictures, including those in the prostatic urethra and bladder neck. MMC injection, in conjunction with traditional DVIU, adds minimally to the complexity and length of the procedure but may substantially improve long-term surgical outcomes.

CONCLUSION

Bladder outlet obstruction due to stenosis or stricture of the posterior urethra is a common urologic diagnosis whose etiology can often be traced to prior urethral manipulation or iatrogenic trauma. While Americal Urological Assicuation (AUA) guidelines state that dilation or direct visualization internal urethrotomy (DVIU) should be offered for bulbar strictures measuring less than 2 cm in length, recent evidence suggests that DVIU with or without MMC injection may have utility in the management of bladder neck or vesicourethral anastomotic contractures. We have found that DVIU with subsequent MMC injection is a viable minimally invasive approach for the treatment of posterior urethral strictures. While more data are needed to better understand the long-term success rates of these procedures, this approach should be considered for patients with a bladder outlet obstruction secondary to a short stricture of the posterior urethra, bladder neck, or vesicourethral anastomosis.

A Multipronged Intervention to Reduce Readmissions and Readmission Intensity After Radical Cystectomy

OBJECTIVE

To develop a multipronged, evidence-based protocol to reduce readmission risk and readmission intensity, as represented by the duration of the index readmission, after radical cystectomy.

MATERIALS AND METHODS

A per-protocol study was performed. The protocol included preoperative nutritional supplementation, early stent removal, and a follow-up phone call within 4-5days of discharge. The preprotocol period was from February 1, 2020 to July 31, 2021 and the postprotocol period was from December 1, 2020 to November 31, 2021. Using multivariate regression models, we compared outcomes among patients treated with radical cystectomy before and after protocol initiation.

RESULTS

We identified 70 preprotocol patients and 126 postprotocol patients. After adjusting for age, sex, BMI, and frailty score, there was a significant reduction in 90-day readmission intensity (7 vs 5days; P = .048) among postprotocol patients.

CONCLUSION

After implementation of an evidence-based protocol for patients undergoing radical 90-day readmission intensity decreased significantly. This protocol may move the needle forward on reducing readmissions, but a larger randomized trial is needed.

Variation in Statewide Intravesical Treatment Rates for Non-Muscle Invasive Bladder Cancer During the Bacillus Calmette-Guerin Drug Shortage

OBJECTIVE

To measure the changes in treatment patterns for non-muscle invasive bladder cancer before and during the Bacillus Calmette-Guerin (BCG) drug shortage.

MATERIALS AND METHODS

We used a 5% random sample of Medicare beneficiaries and identified 7971 bladder cancer patients (2648 pre-BCG shortage and 5323 during the shortage) ≥66 years of age who received intravesical treatment within 1 year of diagnosis between 2010 and 2017. The BCG shortage period was defined from July 2012 ongoing. Full induction treatment with BCG, mitomycin C, gemcitabine, or other intravesical agents was defined as receiving ≥5 of 6 treatments within 60 days. State-level BCG use before and during the drug shortage was compared in US states reporting at least 50 patients in each period. Independent variables included year of index date, age, sex, race, rurality, and region of residence.

RESULTS

BCG utilization rates decreased 5.9% in the shortage period (95% CI (-8.2%)-(-3.7%)). The proportion of patients that completed a full induction course of BCG decreased from 31.0% in the pre-shortage period to 27.6% in the shortage period (P = .002). 84% of reporting states (16 of 19) had decreased BCG utilization ranging between 5% and 36% compared to pre-shortage rates.

CONCLUSION

During the BCG drug shortage, eligible bladder cancer patients were less likely to receive gold standard intravesical BCG with a large variation in treatment patterns between US states.

Changes in Urologic Cancer Surgical Volume and Length of Stay During the COVID-19 Pandemic in Pennsylvania

Importance

Disruptions in cancer surgery during the COVID-19 pandemic led to widespread deferrals and cancellations, creating a surgical backlog that presents a challenge for health care institutions moving into the recovery phase of the pandemic.

Objective

To describe patterns in surgical volume and postoperative length of stay for major urologic cancer surgery during the COVID-19 pandemic.

Design, Setting, and Participants

This cohort study identified 24 001 patients 18 years or older from the Pennsylvania Health Care Cost Containment Council database with kidney cancer, prostate cancer, or bladder cancer who received a radical nephrectomy, partial nephrectomy, radical prostatectomy, or radical cystectomy between the first quarter (Q1) of 2016 and Q2 of 2021. Postoperative length of stay and adjusted surgical volumes were compared before and during the COVID-19 pandemic.

Main Outcomes and Measures

The primary outcome was adjusted surgical volume for radical and partial nephrectomy, radical prostatectomy, and radical cystectomy during the COVID-19 pandemic. The secondary outcome was postoperative length of stay.

Results

A total of 24 001 patients (mean [SD] age, 63.1 [9.4] years; 3522 women [15%], 19 845 White patients [83%], 17 896 living in urban areas [75%]) received major urologic cancer surgery between Q1 of 2016 and Q2 of 2021. Of these, 4896 radical nephrectomy, 3508 partial nephrectomy, 13 327 radical prostatectomy, and 2270 radical cystectomy surgical procedures were performed. There were no statistically significant differences in patient age, sex, race, ethnicity, insurance status, urban or rural status, or Elixhauser Comorbidity Index scores between patients who received surgery before and patients who received surgery during the pandemic. For partial nephrectomy, a baseline of 168 surgeries per quarter decreased to 137 surgeries per quarter in Q2 and Q3 of 2020. For radical prostatectomy, a baseline of 644 surgeries per quarter decreased to 527 surgeries per quarter in Q2 and Q3 of 2020. However, the likelihood of receiving radical nephrectomy (odds ratio [OR], 1.00; 95% CI, 0.78-1.28), partial nephrectomy (OR, 0.99; 95% CI, 0.77-1.27), radical prostatectomy (OR, 0.85; 95% CI, 0.22-3.22), or radical cystectomy (OR, 0.69; 95% CI, 0.31-1.53) was unchanged. Length of stay for partial nephrectomy decreased from baseline by a mean of 0.7 days (95% CI, -1.2 to -0.2 days) during the pandemic.

Conclusions and Relevance

This cohort study suggests that partial nephrectomy and radical prostatectomy surgical volume decreased during the peak waves of COVID-19, as did postoperative length of stay for partial nephrectomy.

Catheter Free Day of Surgery Discharge vs Overnight Observation Following Artificial Urinary Sphincter Placement

Introduction To confirm the safety and examine outcomes of a day of surgery discharge following artificial urinary sphincter implantation in a population discharged without a catheter. Methods We retrospectively identified 110 patients, 31 of whom were discharged on the day of surgery, from a single surgeon following artificial urinary sphincter implantation. After institutional board review approval, patient charts were reviewed capturing demographics as well as three, thirty, and ninety-day outcomes. Further outcomes specific to urinary retention were obtained. Results Patients who were discharged the same day were older (71 vs. 68), had shorter operative times (92 minutes vs 109 minutes), and were less likely to have been smokers (6% vs 31%). There were no differences in the proportion of patients who underwent prior radiation or prior implant surgery. There was no significant difference in the number of patients who had emergency department visits, urinary retention, office calls, office visits, or unplanned office visits at all time points following surgery. There was no significant difference in overall urinary retention (15% vs 5%), retention presenting after the initial surgical event (6% vs 5%), or need for a suprapubic tube (0% vs 5%). Conclusions Day of surgery discharge is a safe discharge strategy for patients who have undergone artificial urinary sphincter placement. Furthermore, catheter-free days of discharge surgery did not have a significantly greater risk of urinary retention, office calls, emergency department (ED) visits, or office visits compared to our overnight observation population. This approach should be considered for all patients undergoing artificial urinary sphincter (AUS) implantation.

The gullwing technique: a novel method of transcorporal artificial urinary sphincter placement for the fragile urethra

OBJECTIVE

To describe the novel gullwing technique for artificial urinary sphincter (AUS) placement. The transcorporal technique for AUS placement is beneficial in patients with 'fragile urethras' (previous failed AUS, urethroplasty or history of radiation) however limitations include insufficient lateral and ventral urethral support in addition to potential cinching during corporotomy closure which, in the absence of additional grafting may restrict our ability to conserve internal corporal capacity and limit options for future preservation of erectile function via penile prosthesis placement. The gullwing variation of the technique offers the potential to circumvent these disadvantages.

MATERIALS AND METHODS

This case describes the gullwing variation of transcorporal AUS placement in a complex patient with a history of abdominopelvic trauma and prior failed AUS placements secondary to urethral erosion.

RESULTS AND CONCLUSION

Transcorporal AUS placement in patients with prior urethral compromise has been shown to result in lower revision and erosion rates. The gullwing modification of the technique is a novel variation providing improved circumferential urethral protection and, with the addition of corporal grafting, aims to enable the preservation of the three-dimensional corporal volume necessary for ease of subsequent penile prosthesis implantation. However, studies assessing the long-term functional outcomes and durability of this technique are needed.

A role for intestinal alkaline phosphatase in preventing liver fibrosis

Rationale: Liver fibrosis is frequently associated with gut barrier dysfunction, and the lipopolysaccharides (LPS) -TLR4 pathway is common to the development of both. Intestinal alkaline phosphatase (IAP) has the ability to detoxify LPS, as well as maintain intestinal tight junction proteins and gut barrier integrity. Therefore, we hypothesized that IAP may function as a novel therapy to prevent liver fibrosis.

Methods: Stool IAP activity from cirrhotic patients were determined. Common bile duct ligation (CBDL) and Carbon Tetrachloride-4 (CCl4)-induced liver fibrosis models were used in WT, IAP knockout (KO), and TLR4 KO mice supplemented with or without exogenous IAP in their drinking water. The gut barrier function and liver fibrosis markers were tested.

Results: Human stool IAP activity was decreased in the setting of liver cirrhosis. In mice, IAP activity and genes expression decreased after CBDL and CCl4 exposure. Intestinal tight junction related genes and gut barrier function were impaired in both models of liver fibrosis. Oral IAP supplementation attenuated the decrease in small intestine tight junction protein gene expression and gut barrier function. Liver fibrosis markers were significantly higher in IAP KO compared to WT mice in both models, while oral IAP rescued liver fibrosis in both WT and IAP KO mice. In contrast, IAP supplementation did not attenuate fibrosis in TLR4 KO mice in either model.

Conclusions: Endogenous IAP is decreased during liver fibrosis, perhaps contributing to the gut barrier dysfunction and worsening fibrosis. Oral IAP protects the gut barrier and further prevents the development of liver fibrosis via a TLR4-mediated mechanism.

Intestinal alkaline phosphatase targets the gut barrier to prevent aging

Gut barrier dysfunction and gut-derived chronic inflammation play crucial roles in human aging. The gut brush border enzyme intestinal alkaline phosphatase (IAP) functions to inhibit inflammatory mediators and also appears to be an important positive regulator of gut barrier function and microbial homeostasis. We hypothesized that this enzyme could play a critical role in regulating the aging process. We tested the role of several IAP functions for prevention of age-dependent alterations in intestinal homeostasis by employing different loss-of-function and supplementation approaches. In mice, there is an age-related increase in gut permeability that is accompanied by increases in gut-derived portal venous and systemic inflammation. All these phenotypes were significantly more pronounced in IAP-deficient animals. Oral IAP supplementation significantly decreased age-related gut permeability and gut-derived systemic inflammation, resulted in less frailty, and extended lifespan. Furthermore, IAP supplementation was associated with preserving the homeostasis of gut microbiota during aging. These effects of IAP were also evident in a second model system, Drosophilae melanogaster. IAP appears to preserve intestinal homeostasis in aging by targeting crucial intestinal alterations, including gut barrier dysfunction, dysbiosis, and endotoxemia. Oral IAP supplementation may represent a novel therapy to counteract the chronic inflammatory state leading to frailty and age-related diseases in humans.

A mechanical model reveals that non-axisymmetric buckling lowers the energy barrier associated with membrane neck constriction

Membrane neck formation is essential for scission, which, as recent experiments on tubules have demonstrated, can be location dependent. The diversity of biological machinery that can constrict a neck such as dynamin, actin, ESCRTs and BAR proteins, and the range of forces and deflection over which they operate, suggest that the constriction process is functionally mechanical and robust to changes in biological environment. In this study, we used a mechanical model of the lipid bilayer to systematically investigate the influence of location, symmetry constraints, and helical forces on membrane neck constriction. Simulations from our model demonstrated that the energy barriers associated with constriction of a membrane neck are location-dependent. Importantly, if symmetry restrictions are relaxed, then the energy barrier for constriction is dramatically lowered and the membrane buckles at lower values of forcing parameters. Our simulations also show that constriction due to helical proteins further reduces the energy barrier for neck formation when compared to cylindrical proteins. These studies establish that despite different molecular mechanisms of neck formation in cells, the mechanics of constriction naturally leads to a loss of symmetry that can lower the energy barrier to constriction.

No need for surgery? Patterns and outcomes of blunt abdominal trauma

Introduction

The management of a patient suffering from blunt abdominal trauma (BAT) remains a challenge for the emergency physician. Within the last few years, the standard therapy for hemodynamically stable patients with BAT has transitioned to a non-operative approach. The purpose of this study is to evaluate the outcome of patients with BAT and to determine the reasons for failure of non-operative management (NOM).

Materials and methods

Analysis of 176 consecutive patients treated for BAT was conducted in a German level 1 trauma center from 2004 to 2011. Abdominal injuries were classified according to the American Association for the Surgery of Trauma (AAST). Patients included were demonstrated to have objective abdominal trauma with either free fluid on focused assessment with sonography for trauma (FAST) or computed tomography (CT), or proven organ injury.

Results

Patients, 142 of 176 (80.7%), with BAT were initially managed non-operatively, with a success rate of 90%. The rates of NOM success were higher among those with less severe injuries; 100% with Abbreviated Injury Scale (AIS) of 1. In total, 125 patients (71.0%) were managed non-operatively, and 51 (29.0%) required surgical intervention. NOM failure occurred in 9.2% of the patients, the most common reason being initially undiagnosed intestinal perforation (46.2%). Positive correlation was identified (r = 0.512; p < 0.001) between the ISS (injury severity score) and the NACA (National Advisory Committee of Aeronautics) score. The delay in operation in NOM failure was 6 h in patients with underlying hepatic or splenic rupture and 34 h with intestinal perforation. The overall mortality of 5.1% was attributed especially to old age (p = 0.016), high severity of injury (p < 0.001), and greater need for blood transfusion (p < 0.001).

Conclusion

NOM was successful for the vast majority of blunt abdominal trauma patients, especially those with less severe injuries. NOM failure and operative delay were most commonly due to occult hollow viscus injury (HVI), the detection of which was achieved by close clinical observation and abdominal ultrasound in conjunction with monitoring for rising markers of infection and by multidetector computed tomography (MDCT) if additionally indicated. Based on this concept, the delay in operation in patients with NOM failure was short. This study underscores the feasibility and benefit of NOM in BAT.

The role of traction in membrane curvature generation

Curvature of biological membranes can be generated by a variety of molecular mechanisms including protein scaffolding, compositional heterogeneity, and cytoskeletal forces. These mechanisms have the net effect of generating tractions (force per unit length) on the bilayer that are translated into distinct shapes of the membrane. Here, we demonstrate how the local shape of the membrane can be used to infer the traction acting locally on the membrane. We show that buds and tubes, two common membrane deformations studied in trafficking processes, have different traction distributions along the membrane and that these tractions are specific to the molecular mechanism used to generate these shapes. Furthermore, we show that the magnitude of an axial force applied to the membrane as well as that of an effective line tension can be calculated from these tractions. Finally, we consider the sensitivity of these quantities with respect to uncertainties in material properties and follow with a discussion on sources of uncertainty in membrane shape.

Changing roles of grass-root level health workers in Kerala, India

OBJECTIVE

Multipurpose health workers (MPWs) are envisioned as key personnel in the delivery of primary health care. We evaluated their role and participation in implementing different national health programmes in Kerala, INDIA:

DESIGN

Cross-sectional, community-based survey.

PARTICIPANTS

We selected three out of the 14 districts in KERALA: Three-hundred and twenty-six MPWs (95 male and 231 female) from 44 randomly selected primary health centres from the three districts were questioned using a structured pre-tested questionnaire that sought information regarding the provision of health services by the MPWs to eligible beneficiaries in the community. We randomly selected 90 subcentres (30 from each district) and 750 households using a cluster sampling technique, and conducted household surveys to compare the actual delivery of services at the doorstep with that reported by the MPWS: Work sampling of MPWs was also performed to examine the fieldwork time spent by them on implementing individual national health programmes. These data were supplemented with focus group discussions and personal interviews of MPWs and household members.

RESULTS

MPWs consistently 'over-reported' their performance when self-reported information was compared with that obtained from household surveys. Male MPWs concentrated on the National Malaria Eradication Programme and health education while female workers focused on the family welfare and immunization programmes. Key national health programmes (such as for tuberculosis and acute respiratory infection) were neglected by all MPWS: MPWs were aware of health problems of the elderly, but were not adequately trained nor officially expected to deliver any services in these fields.

CONCLUSIONS

Grass-root level workers apportion more time to select national health programmes to the detriment of other health programmes, thereby negating their multipurpose role. Our study emphasizes the need for interventions to derive 'multipurpose benefits' from the MPWS:

Inositol polyphosphates regulate Ca2+ efflux in a cardiac membrane subtype distinct from junctional sarcoplasmic reticulum

The membrane location and mechanism of inositol 1,3,4,5-tetrakisphosphate (InsP4)-regulated Ca2+ uptake in cardiac membrane vesicles was investigated. In canine and rat membranes separated by sucrose density gradient centrifugation, InsP4-regulated Ca2+ uptake was slightly more enriched in low density than in higher density membranes. Membranes supporting InsP4-regulated Ca2+ uptake were correspondingly enriched in type 1 InsP3 receptors. Junctional sarcoplasmic reticulum (J-SR), enriched in sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) and ryanodine receptors, separated predominantly with higher density membranes. In membranes supporting InsP4-regulated Ca2+ uptake, Ca2+ uptake was facilitated by a high Ca2+ affinity carrier that was insensitive to thapsigargin. Ca2+ uptake in J-SR was mediated by thapsigargin-sensitive SERCA2a. Net Ca accumulation was enhanced by oxalate in both SR subtypes. Although Ca2+-carrier-mediated Ca2+ uptake was ATP independent, ATP indirectly regulated net Ca2+ accumulation by modifying Ca2+ efflux via a Ca2+ channel with properties of type 1 InsP3 receptors. In the presence of < or = 0.1 mM ATP, InsP4 enhanced Ca2+ accumulation whereas InsP4 inhibited Ca2+ uptake at higher ATP concentrations. In the presence of 0.15 mM ATP, InsP4 stimulated Ca2+ efflux from vesicles preloaded with Ca. Several other InsP4 isomers and 1,3,4-InsP3 also stimulated Ca2+ efflux but with slightly less potency than 1,3,4,5-InsP4. Ruthenium red enhanced net Ca accumulation by the Ca2+ carrier and reduced the potency of ATP, InsP4, and InsP3 to stimulate Ca2+ efflux in vesicles. In summary, this investigation shows that a Ca2+ carrier facilitates Ca loading in a sarcoplasmic reticulum subtype distinct from J-SR. InsP4 and InsP3 are proposed to regulate Ca2+ efflux in low density SR by acting on an ATP-modulated Ca2+ channel with properties of type 1 InsP3 receptors.

Regulation of guanine nucleotide turnover on Gi/Go by agonist-stimulated and spontaneously active muscarinic receptors in cardiac membranes

Muscarinic receptor regulation of guanine nucleotide turnover on Gi/Go proteins in ventricular sarcolemma was investigated. In the absence of a muscarinic receptor (MR) agonist, GTP bound to background sites with a Kapp value of 60 nM and a Bmax of 50 pmol/mg. The addition of the MR agonist, carbachol, further increased GTP binding by 50 pmol/mg to sites with the same Kapp value of 60 nM. Pertussis toxin treatment reduced GTP binding to carbachol-regulated and background binding sites, thus identifying both sites as Gi/Go. The identity of the carbachol-regulated GTP binding sites was further confirmed by demonstrating that carbachol stimulated GTP binding and inhibited adenylyl cyclase with an EC50 value of 200 nM. Background and carbachol-regulated guanine nucleotide binding sites bound GDP with a Kapp value of 150 nM. However, maximal background GDP binding was 50 pmol/mg, whereas maximal carbachol-regulated GDP binding was only 12-15 pmol/mg. In sarcolemma preloaded with [3H]GDP, carbachol-regulated [3H]GDP release was strictly dependent on the presence of guanine nucleotides. The Kapp values for GTP and GDP to support carbachol-regulated [3H]GDP release were 60 nM and 150 nM, respectively. Guanosine 5'-O-(3-thiotriphosphate) (GDPbetaS) facilitated carbachol-regulated [3H]GDP release with a Kapp value of 2 microM. However, GTP was two times more efficacious than GDP or GDPbetaS in facilitating carbachol-regulated [3H]GDP release. Mn2+ also stimulated [3H]GDP release from carbachol-regulated sites by a mechanism not requiring guanine nucleotides. These studies indicate that two pools of muscarinic receptors, carbachol regulated and spontaneously active, regulate guanine nucleotide turnover on pertussis toxin sensitive Gi/Go. These studies further suggest that guanine nucleotide binding provides the signal to stimulate GDP release from receptor activated Gi/Go proteins. A quaternary mechanism involving G-protein interactions may be necessary to promote guanine nucleotide exchange on Gi/Go.

Mechanisms of prostaglandin F2 alpha and histamine-induced contractions in human chorionic vasculature

We investigated the signaling pathways modulating histamine- and prostaglandin F2 alpha (PGF2 alpha)-induced contractions of human chorionic vasculature. Neomycin, a phospholipase C (PLC) inhibitor, attenuated PGF2 alpha and histamine contractile responses 40 and 60%, respectively. AIF4-, a G protein stimulant, induced a strong contraction alone but blocked histamine- and PGF2 alpha-induced contractions. Staurosporine (100 nM), a protein kinase C (PKC) inhibitor, attenuated the PGF2 alpha-dependent contractions by 50% but did not affect the histamine response. However, higher nonspecific inhibitory concentrations of staurosporine (1-2 microM) abolished histamine and PGF2 alpha contractile responses, presumably by inhibiting other protein kinases. Although, the PKC phorbol 12-myristate 13-acetate (PMA) did not affect basal tension or PGF2 alpha-dependent contractions, the histamine response was attenuated by 30%. Sodium nitroprusside (SNP), a guanylyl cyclase stimulant, strongly attenuated histamine- and PGF2 alpha-induced contractions. Tension increases were similarly attenuated by forskolin and isobutylmethylxanthine (IBMX), which increase intracellular cyclic AMP. In vessel rings prelabeled with [3H]myoinositol, PGF2 alpha and histamine increased [3H]inositol phosphate (IP) production 400 and 100%, respectively, indicating that PLC is stimulated by both agonists. Neomycin inhibited histamine- and PGF2 alpha-induced increases in [3H]IP production 60 and 40%, respectively. Staurosporine (0.1-1 microM) and PMA did not affect histamine- or PGF2 alpha-stimulated IP production. AIF4-alone increased IP production but blocked histamine- and PGF(2 alpha)-dependent IP increases. These observations suggest that at least part of the contractile responses due to PGF2 alpha and histamine are associated with stimulation of PLC through an AIF4(-)-sensitive G protein. The role of PKC is variable, because PGF2 alpha but not histamine tension responses were attenuated by PKC inhibition. In addition, therapeutic agents that increase cyclic AMP and cyclic GMP attenuated histamine- and PGF2 alpha-induced contractions in human chorionic vasculature, although histamine responses were relatively more sensitive to these agents.

Inositol tetrakisphosphate stimulates a novel ATP-independent Ca2+ uptake mechanism in cardiac junctional sarcoplasmic reticulum

The effects of inositol phosphates on Ca2+ uptake in cardiac junctional sarcoplasmic reticulum (JSR) vesicles was investigated. Inositol 1,3,4,5-tetrakisphosphate (IP4) selectively increased Ca2+ uptake 2.8 fold over basal levels whereas 1,3,4-IP3, 1,4,5-IP3 or 1,4-IP2 were without effect. Stimulation of Ca2+ uptake by IP4 was maximal within 15-60 sec at 30 degrees C and ATP-independent. Following incubation of JSR with ruthenium red, Ca2+ uptake in the presence or absence of IP4 was further enhanced 2.5 fold. Both basal and IP4-stimulated Ca2+ uptake were half-maximal and maximal in the presence of 60 nM and 180 nM Ca2+, respectively. These studies indicate that IP4 stimulates an ATP-independent Ca2+ uptake mechanism in cardiac JSR which may function to promote rapid Ca2+ loading.

Chronic sympathectomy of canine cardiac ventricles affects Gs-adenylyl cyclase coupling and muscarinic receptor density

The effect of chronic ventricular sympathectomy on sarcolemmal muscarinic receptor (MR) and beta-adrenoceptor densities and coupling of these receptors to adenylyl cyclase was examined. Microsomal membranes were isolated from right and left ventricles of control dogs (sham- and nonoperated) and dogs with ventricles sympathectomized 4 weeks earlier. Relative to control membranes, MR density was decreased in left but not right ventricular (LV, RV) membranes from sympathectomized hearts. Relative carbachol inhibition of adenylyl cyclase was similar in RV and LV membranes from both heart groups, however, Although beta-adrenoceptor densities and ratio of beta 1- and beta 2-adrenoceptor subtypes did not change, basal adenylyl cyclase activity was 40% less in sympathectomized membranes as compared with control membranes. Furthermore, relative stimulation of adenylyl cyclase by isoproterenol was twofold greater in sympathectomized heart membranes. Because maximally stimulated adenylyl cyclase activity by NaF or MnCl2 was identical in sympathectomized and control membranes, the reduction in basal activity may not be related to a decrease in Gs and adenylyl cyclase. In support of this hypothesis, Gs alpha content as estimated from optimal cholera toxin-catalyzed ADP-ribosylation was similar in control and sympathectomized membranes. Therefore, an alteration in Gs interaction with adenylyl cyclase may account for the reduction in basal adenylyl cyclase activity and the increased relative responsiveness of adenylyl cyclase to isoproterenol in chronically sympathectomized ventricular membranes.

Modification of cardiac membrane adenylate cyclase activity and Gs alpha by NAD and endogenous ADP-ribosyltransferase

The mechanism by which NAD stimulates cardiac adenylate cyclase was investigated. In highly purified canine cardiac sarcolemma, NAD stimulated adenylate cyclase activity in the presence of agents which activate Gs (i.e. 5 mM AlF4-, 10 microM GTP gamma S, 10 microM GppNHp or isoproterenol plus 2 nM GTP gamma S). Furthermore, the EC50 of isoproterenol to stimulate adenylate cyclase was reduced in the presence of NAD. In membranes incubated with [32P]-NAD, AlF4-, 10 microM GTP gamma S or isoproterenol plus 2 nM GTP gamma S produced a selective increase in the radiolabeling of a single 45-kDa protein which was identified as Gs alpha by immunoprecipitation. Cholera toxin catalysed radiolabeling of the same protein. Neutral hydroxylamine released [32P]-ADP-ribose from Gs alpha prelabeled in the presence of AlF4- and [32P]-NAD indicating that an arginine residue on Gs alpha was modified by an endogenous ADP-ribosyltransferase. ADP-ribosyltransferase inhibitors, novobiocin, vitamin K1 or 3-aminobenzamide, inhibited AlF4- stimulated ADP-ribosylation of Gs alpha and NAD potentiation of adenylate cyclase with similar efficacies. The activity responsible for NAD potentiation of adenylate cyclase and ADP-ribosylation of Gs alpha was not removed under hypotonic or hypertonic conditions and therefore appears to be tightly membrane bound. Collectively, these observations indicate that canine cardiac sarcolemma possess an ADP-ribosyltransferase which may constitutively catalyse transfer of an ADP-ribose to activated Gs alpha.

Guanylnucleotide specificity for muscarinic receptor inhibitory coupling to cardiac adenylate cyclase

The guanylnucleotide specificity of muscarinic acetylcholine receptor (MR) inhibitory coupling to cardiac adenylate cyclase (AC) was investigated under low MgCl2 (i.e., 0.5 mM) conditions. In purified cardiac sarcolemma, carbachol maximally inhibited AC activity 60% in the presence of GTP. Carbachol-dependent inhibition in the presence of guanosine 5'-O-(3-thiotriphosphate (GTP gamma S) or guanylylimidodiphosphate [Gpp(NH)p] was of lesser magnitude (i.e., 30%) and was evident only during short incubation periods. Of greater interest, carbachol maximally inhibited AC activity in the presence of GDP and guanosine 5'-O-(2-thiodiphosphate (GDP beta S) by 35 and 60%, respectively. Control studies ruled out transphosphorylation of GDP and GDP beta S by nucleoside diphosphate kinase or guanylnucleoside triphosphate contamination as reasons for the inhibitory effects of GDP and GDP beta S. Furthermore, isoproterenol stimulated AC in the presence of GTP, GTP gamma S, and Gpp(NH)p but not in the presence of GDP or GDP beta S. Therefore, GDP and GDP beta S may serve as agonists on MR-activated Gi but not on beta-adrenergic receptor-activated Gs in these membranes. Time course studies revealed that carbachol-dependent inhibition of AC in the presence of either GTP or GDP occurred without a detectable lag period, and this inhibition was rapidly reversed by atropine. In contrast, a 1-2-min lag time was required for carbachol- and GDP beta S-dependent inhibition of AC to occur, and inhibition, once developed, was only partially and slowly reversed by atropine. Preincubation of sarcolemma with carbachol and GDP beta S, in the absence of ATP or under nonphosphorylating conditions, eliminated the lag time for inhibition of AC activity. Although it is unlikely that GDP and GDP beta S have physiological relevance of MR-Gi-AC coupling, these studies provide unique insights into this coupling mechanism in cardiac membranes.

Amino acid transport in kidney epithelial cell line (MDCK): characteristics of Na+/amino acid symport in membrane vesicles and basolateral localization in cell monolayers

Na+-stimulated amino acid transport was investigated in MDCK kidney epithelial cell monolayers and in isolated membrane vesicles. When transport polarity was assessed in confluent polarized epithelial cell monolayers cultured on Nucleopore filters and mounted between two lucite chambers, Na+-stimulated transport of 2-(methylamino)isobutyric acid (MeAIB), a substrate specific for the A system, was predominantly localized on the basolateral membrane. Na+-stimulated amino acid transport activity was maximal in subconfluent cultures, and was substantially reduced after confluence. A membrane vesicle preparation was isolated from confluent MDCK cell cultures which was enriched in Na+-stimulated MeAIB transport activity and Na+,K+,ATPase activity, a basolateral marker, but was not enriched in apical marker enzyme activities or significantly contaminated by mitochondria. Na+-coupled amino acid transport activity assayed in vesicles exhibited a marked dependence on external pH, with an optimum at pH 7.4. The pattern of competitive interactions among neutral amino acids was characteristic of A system transport. Na+-coupled MeAIB and AIB transport in vesicles was electrogenic, stimulated by creation of an interior-negative membrane potential. The Na+ dependence of amino acid transport in vesicles suggested a Na+ symport mechanism with a 1:1 stoichiometry between Na+ and amino acid.