Citations

The purpose of this study was to examine whether the nitric oxide donor S-nitrosoglutathione (GSNO) relaxes canine tracheal smooth muscle (CTSM) strips by decreasing Ca 2+ sensitivity [i.e., the amount of force for a given intracellular Ca 2+ concentration ([Ca 2+ ] i )]. We further investigated whether GSNO decreases Ca 2+ sensitivity by altering the relationship between regulatory myosin light chain (rMLC) phosphorylation and [Ca 2+ ] i and the relationship between force and rMLC phosphorylation. GSNO (100 μM) relaxed intact CTSM strips contracted with 45 mM KCl by decreasing Ca 2+ sensitivity in comparison to control strips without significantly decreasing [Ca 2+ ] i . GSNO reduced the amount of rMLC phosphorylation for a given [Ca 2+ ] i but did not affect the relationship between isometric force and rMLC phosphorylation. These results show that in CTSM strips contracted with KCl, GSNO decreases Ca 2+ sensitivity by affecting the level of rMLC phosphorylation for a given [Ca 2+ ] i , suggesting that myosin light chain kinase is inhibited or that smooth muscle protein phosphatases are activated by GSNO.

In airway smooth muscle (ASM), ACh induces propagating intracellular Ca2+concentration ([Ca2+]i) oscillations (5–30 Hz). We hypothesized that, in ASM, coupling of elevations and reductions in [Ca2+]ito force generation and relaxation (excitation-contraction coupling) is slower than ACh-induced [Ca2+]ioscillations, leading to stable force generation. When we used real-time confocal imaging, the delay between elevated [Ca2+]iand contraction in intact porcine ASM cells was found to be ∼450 ms. In β-escin-permeabilized ASM strips, photolytic release of caged Ca2+resulted in force generation after ∼800 ms. When calmodulin (CaM) was added, this delay was shortened to ∼500 ms. In the presence of exogenous CaM and 100 μM Ca2+, photolytic release of caged ATP led to force generation after ∼80 ms. These results indicated significant delays due to CaM mobilization and Ca2+-CaM activation of myosin light chain kinase but much shorter delays introduced by myosin light chain kinase-induced phosphorylation of the regulatory myosin light chain MLC20and cross-bridge recruitment. This was confirmed by prior thiophosphorylation of MLC20, in which force generation occurred ∼50 ms after photolytic release of caged ATP, approximating the delay introduced by cross-bridge recruitment alone. The time required to reach maximum steady-state force was >15 s. Rapid chelation of [Ca2+]iafter photolytic release of caged diazo-2 resulted in relaxation after a delay of ∼1.2 s and 50% reduction in force after ∼57 s. We conclude that in ASM cells agonist-induced [Ca2+]ioscillations are temporally and spatially integrated during excitation-contraction coupling, resulting in stable force production.

The multiplicity of mechanisms involved in regulation of intracellular Ca2+concentration ([Ca2+]i) in smooth muscle results in both intra- and intercellular heterogeneities in [Ca2+]i. Heterogeneity in [Ca2+]iregulation is reflected by the presence of spontaneous, localized [Ca2+]itransients (Ca2+sparks) representing Ca2+release through ryanodine receptor (RyR) channels. Ca2+sparks display variable spatial Ca2+distributions with every occurrence within and across cellular regions. Individual sparks are often grouped, and fusion of sparks produces large local elevations in [Ca2+]ithat occasionally trigger propagating [Ca2+]iwaves. Ca2+sparks may modulate membrane potential and thus smooth muscle contractility. Sparks may also be the target of other regulatory factors in smooth muscle. Agonists induce propagating [Ca2+]ioscillations that originate from foci with high spark incidence and also represent Ca2+release through RyR channels. With increasing agonist concentration, the peak of regional [Ca2+]ioscillations remains relatively constant, whereas both frequency and propagation velocity increase. In contrast, the global cellular response appears as a concentration-dependent increase in peak as well as mean cellular [Ca2+]i, representing a spatial and temporal integration of the oscillations. The significance of agonist-induced [Ca2+]ioscillations lies in the establishment of a global [Ca2+]ilevel for slower Ca2+-dependent physiological processes.

AbstractPharmacokinetics and antithrombotic effects of the Factor Xa inhibitor rivaroxaban were studied in subjects with mild renal insufficiency concurrently taking the P‐glycoprotein and moderate CYP3A inhibitor verapamil, a drug commonly administered to patients with hypertension, ischemic heart disease, or atrial fibrillation. Age‐matched controls with normal renal function were studied concurrently. Subjects’ overall mean age was 59 years. Mean creatinine clearance values in the 2 groups were 105 and 71 mL/min. After single 20‐mg oral doses, rivaroxaban area under the curve (AUC) was increased by a factor of 1.11 (ratio of geometric means [RGM]) in mild renal insufficiency compared to controls. Verapamil coadministration independently increased AUC to the same extent in both the mild renal insufficiency and control groups (RGM, 1.39 and 1.43). Concurrent mild renal insufficiency and verapamil produced additive inhibition compared to controls without verapamil (RGM, 1.58). Prothrombin time (PT) prolongation and Factor Xa inhibition tracked plasma rivaroxaban, and were enhanced by verapamil. Concentration–response relationships for PT (linear) and Factor Xa inhibition (hyperbolic) were unaffected by renal function or verapamil. The absolute and relative increases in rivaroxaban AUC caused by verapamil in mild renal insufficiency subjects are potentially associated with an increased bleeding risk. Modification of recommended dosage may be required in this combination of circumstances to reduce risk to patients.

Anderson, Paul J., Christina M. Wood-Wentz, Kent R. Bailey, and Bruce D. Johnson. Objective versus self-reported sleep quality at high altitude. High Alt Med Biol . 24:144–148, 2023. Background: Previous studies have found little relationship between polysomnography and a diagnosis of acute mountain sickness (AMS) using the Lake Louise Symptom Questionnaire (LLSQ). The correlation between sleep question responses on the LLSQ and polysomnography results has not been explored. We compared LLSQ sleep responses and polysomnography data from our previous study of workers rapidly transported to the South Pole. Methods: Sixty-three subjects completed a 3-hour flight from sea level to the South Pole (3200 m, 9800 ft). Participants completed limited overnight polysomnography on their first night and completed LLSQ upon awakening. We compared polysomnography results at the South Pole with sleep question responses on the LLSQ to assess their degree of correspondence. Results: Twenty-two (30%) individuals reported no sleep problems whereas 20 (32%) reported some problems and 20 (33%) individuals reported poor sleep and 1 reported no sleep ( n = 1). Median sleep efficiency was (94%) among response groups and mean overnight oxygen saturation was 81%. Median apnea hypopnea index (AHI; events/hour) was 10.2 in those who reported no problems sleeping, 5.1 in those reporting some problems sleeping, and 13.7 in those who reported poor sleep. These differences were not statistically significant. Conclusion: Self-reported sleep quality varied but there were no associated significant differences in sleep efficiency, overnight oxygen saturation, nor AHI. Studies that explore the role of objective sleep quality in the development of AMS should remove the sleep question on the LLSQ from AMS scoring algorithms.

Treatment with cisplatin and gemcitabine demonstrates a survival benefit in patients with advanced biliary tract cancer (ABTC). However, the weekly administration can add significant toxicities that may prohibit prolonged treatment. Based on previous studies, we implemented a modified biweekly regimen of GC in an attempt to optimize the prescribed regimen with an improved toxicity profile, added convenience to patients while maintaining efficacy. Patients with ABTC were treated with fixed dose rate (FDR) gemcitabine (1,000 mg/m2/min) and cisplatin 20 mg/m2 on days 1 and 15 of every 28‐day cycle. Patients received treatment until time of progression, death, or discontinuation due to intolerance. Collected data included demographics, clinico‐pathologic features, toxicities, and survival. Kaplan‐Meier curves were used to calculate the median overall survival (OS) and progression free survival (PFS). The study included 107 evaluable pts with unresectable ABTC who received the biweekly regimen. Sites of tumor included gallbladder (21.5%), ampullary (3.7%), and bile duct (74.8%). Median number of cycles was 6 (1–27). Median PFS was 8.34 (6.74, 9.23) months and median OS was 10.32 (9.10, 11.43) months. Most common grade ≥3 adverse events included neutropenia (11%), fatigue (10%), and thrombocytopenia (6.4%). Biweekly FDR GC in ABTC is associated with a more favorable toxicity profile while maintaining efficacy similar to that observed in prior clinical trials. Minimal toxicities were observed despite a prolonged course for many patients. Further prospective trials should consider evaluating the role of biweekly GC regimen in ABTC, including a potentially more favorable platform in novel experimental strategies.