The functional role of protease-activated receptors on contractile responses by activation of Ca2+ sensitization pathways in simian colonic muscles.

It has been known that activation of protease-activated receptors (PARs) affects gastrointestinal motility. In this study, we tested the effects of PAR agonists on electrical and contractile responses and Ca2+ sensitization pathways in simian colonic muscles. The Simian colonic muscle was initially hyperpolarized by PAR agonists. After the transient hyperpolarization, simian colonic muscle repolarized to the control resting membrane potential (RMP) without a delayed depolarization. Apamin significantly reduced the initial hyperpolarization, suggesting that activation of small conductance Ca2+-activated K+ (SK) channels is involved in the initial hyperpolarization. In contractile experiments, PAR agonists caused an initial relaxation followed by an increase in contractions. These delayed contractile responses were not matched with the electrical responses that showed no after depolarization of the RMP. To investigate the possible involvement of Rho-associated protein kinase 2 (ROCK) pathways in the PAR effects, muscle strips were treated with ROCK inhibitors, which significantly reduced the PAR agonist-induced contractions. Furthermore, PAR agonists increased MYPT1 phosphorylation, and ROCK inhibitors completely blocked MYPT1 phosphorylation. PAR agonists alone had no effect on CPI-17 phosphorylation. In the presence of apamin, PAR agonists significantly increased CPI-17 phosphorylation, which was blocked by protein kinase C (PKC) inhibitors suggesting that Ca2+ influx is increased by apamin and is activating PKC. In conclusion, these studies show that PAR activators induce biphasic responses in simian colonic muscles. The initial inhibitory responses by PAR agonists are mainly mediated by activation of SK channels and delayed contractile responses are mainly mediated by the CPI-17 and ROCK Ca2+ sensitization pathways in simian colonic muscles. NEW & NOTEWORTHY In the present study, we found that the contractile responses of simian colonic muscles to protease-activated receptor (PAR) agonists are different from the previously reported contractile responses of murine colonic muscles. Ca2+ sensitization pathways mediate the contractile responses of simian colonic muscles to PAR agonists without affecting the membrane potential. These findings emphasize novel mechanisms of PAR agonist-induced contractions possibly related to colonic dysmotility in inflammatory bowel disease.

How much experience do rescuers require to achieve successful tracheal intubation during cardiopulmonary resuscitation?

AIM: The cardiopulmonary resuscitation (CPR) guidelines recommend that endotracheal intubation (ETI) should be performed only by highly skilled rescuers. However, the definition of 'highly skilled' is unclear. This study evaluated how much experience with ETI is required for rescuers to perform successful ETI quickly without complications including serious chest compression interruption (interruption time <10 s) or oesophageal intubation during CPR. METHODS: This was a clinical observation study using review of CPR video clips in an urban emergency department (ED) over 2 years. Accumulated ETI experience and performance of ETI were analysed. Main outcomes were 1) 'qualified ETI': successful ETI within 60 s without complications and 2) 'highly qualified ETI': successful ETI within 30 s without complications. RESULTS: We analysed 110 ETIs using direct laryngoscopy during CPR. The success rate improved and the time to successful ETI decreased with increasing experience; however, the total interruption time of chest compression did not decrease. A 90% success rate for qualified ETI required 137 experiences of ETIs (1218 days of training). A 90% success rate for highly qualified ETI required at least 243 experiences of ETIs (1973 days of training). CONCLUSIONS: Accumulated experience can improve the ETI success rate and time to successful ETI during CPR. Because ETI must be performed quickly without serious interruption of chest compression during CPR, becoming proficient at ETI requires more experience than that required for non-arrest patients. In our analysis, more than 240 experiences were required to achieve a 90% success rate of highly qualified ETI.