Protein kinase C (PKC)-mediated phosphorylation of cardiac myofilament (MF) proteins has been shown to depress the actomyosin interaction and may be important during heart failure. Biochemical studies indicate that phosphorylation of Ser43 and Ser45 of cardiac troponin I (cTnI) plays a substantial role in the PKC-mediated depression. We studied intact and detergent-extracted papillary muscles from nontransgenic (NTG) and transgenic (TG) mouse hearts that express a mutant cTnI (Ser43Ala, Ser45Ala) that lacks specific PKC-dependent phosphorylation sites. Treatment of NTG papillary muscles with phenylephrine (PE) resulted in a transient increase and a subsequent 62% reduction in peak twitch force. TG muscles showed no transient increase and only a 45% reduction in force. There was a similar difference in maximum tension between NTG and TG fiber bundles that had been treated with a phorbol ester and had received subsequent detergent extraction. Although levels of cTnI phosphorylation correlated with these differences, the TG fibers also demonstrated a decrease in phosphorylation of cardiac troponin T. The PKC-specific inhibitor chelerythrine inhibited these responses. Our data provide evidence that specific PKC-mediated phosphorylation of Ser43 and Ser45 of cTnI plays an important role in regulating force development in the intact myocardium.

In pediatric acute respiratory distress syndrome, early deaths were due primarily to neurologic failure, whereas later deaths were more commonly due to multisystem organ failure. Deaths from neurologic causes accounted for a substantial portion of nonsurvivors. Refractory hypoxemia accounted for only a minority of deaths. Our study highlights limitations associated with using death as an endpoint in therapeutic pediatric acute respiratory distress syndrome trials.

Objective Literature regarding appropriate use of inhaled nitric oxide (iNO) for pediatric acute respiratory distress syndrome (PARDS) is sparse. This study aims to determine if positive response to iNO is associated with decreased mortality and duration of mechanical ventilation in PARDS. Design Retrospective cohort study Setting Large pediatric academic medical center Patients or Subjects 161 children with PARDS and iNO exposure for ≥1 hour within 3 days of PARDS onset. Interventions Patients with ≥20% improvement in oxygenation index (OI) or oxygen saturation index (OSI) by 6 hours after iNO initiation were classified as “responders.” Measurements and Main Results OI, OSI, and ventilator settings were evaluated prior to iNO initiation and 1, 6, 12, and 24 hours following iNO initiation. Primary outcomes were mortality and duration of mechanical ventilation. Baseline characteristics, including severity of illness, were similar between responders and non-responders. Univariate analysis showed no difference in mortality between responders and non-responders (21% vs 21%, p=0.999). Ventilator days were significantly lower in responders (10 vs 16, p<0.001). Competing risk regression (competing risk of death) confirmed association between iNO response and successful extubation (SHR=2.11, 95% CI 1.41 to 3.17, p<0.001). Response to iNO was associated with decreased utilization of high frequency oscillatory ventilation (HFOV) and extracorporeal membrane oxygenation (ECMO), and lower hospital charges (difference in medians of $424,000). Conclusions Positive response to iNO was associated with fewer ventilator days, without change in mortality, potentially via reduced use of HFOV and ECMO. Future studies of iNO for PARDS should stratify based on oxygenation response, given the association with favorable outcomes.