Professor Dirk Van Helden

Lee JM, Mayall JR, Chevalier A, McCarthy H, Van Helden D, Hansbro PM, Horvat JC, Jobling P. Chlamydia muridarum infection differentially alters smooth muscle function in mouse uterine horn and cervix. Am J Physiol Endocrinol Metab 318: E981 E994, 2020. First published April 21, 2020; doi:10.1152/ajpendo.00513. 2019. Chlamydia trachomatis infection is a primary cause of reproductive tract diseases including infertility. Previous studies showed that this infection alters physiological activities in mouse oviducts. Whether this occurs in the uterus and cervix has never been investigated. This study characterized the physiological activities of the uterine horn and the cervix in a Chlamydia muridarum (Cmu)-infected mouse model at three infection time points of 7, 14, and 21 days postinfection (dpi). Cmu infection significantly decreased contractile force of spontaneous contraction in the cervix (7 and 14 dpi; P < 0.001 and P < 0.05, respectively), but this effect was not observed in the uterine horn. The responses of the uterine horn and cervix to oxytocin were significantly altered by Cmu infection at 7 dpi (P < 0.0001), but such responses were attenuated at 14 and 21 dpi. Cmu infection increased contractile force to prostaglandin (PGF2_) by 53 83% in the uterine horn. This corresponded with the increased messenger ribonucleic acid (mRNA) expression of Ptgfr that encodes for its receptor. However, Cmu infection did not affect contractions of the uterine horn and cervix to PGE2 and histamine. The mRNA expression of Otr and Ptger4 was inversely correlated with the mRNA expression of Il1b, Il6 in the uterine horn of Cmu-inoculated mice (P < 0.01 to P < 0.001), suggesting that the changes in the Otr and Ptger4 mRNA expression might be linked to the changes in inflammatory cytokines. Lastly, this study also showed a novel physiological finding of the differential response to PGE2 in mouse uterine horn and cervix.

Calmodulin (CaM) is a Ca-binding protein that binds to, and can directly inhibit cardiac ryanodine receptor calcium release channels (RyR2). Animal studies have shown that RyR2 hyperphosphorylation reduces CaM binding to RyR2 in failing hearts, but data are lacking on how CaM regulates human RyR2 and how this regulation is affected by RyR2 phosphorylation. Physiological concentrations of CaM (100 nM) inhibited the diastolic activity of RyR2 isolated from failing human hearts by ~50% but had no effect on RyR2 from healthy human hearts. Using FRET between donor-FKBP12.6 and acceptor-CaM bound to RyR2, we determined that CaM binds to RyR2 from healthy human heart with a K d = 121 ± 14 nM. Ex-vivo phosphorylation/dephosphorylation experiments suggested that the divergent CaM regulation of healthy and failing human RyR2 was caused by differences in RyR2 phosphorylation by protein kinase A and Ca-CaM-dependent kinase II. Ca 2+ -spark measurements in murine cardiomyocytes harbouring RyR2 phosphomimetic or phosphoablated mutants at S2814 and S2808 suggest that phosphorylation of residues corresponding to either human RyR2-S2808 or S2814 is both necessary and sufficient for RyR2 regulation by CaM. Our results challenge the current concept that CaM universally functions as a canonical inhibitor of RyR2 across species. Rather, CaM's biological action on human RyR2 appears to be more nuanced, with inhibitory activity only on phosphorylated RyR2 channels, which occurs during exercise or in patients with heart failure.

Neural and agonist-induced contractions of proximal (i.e. upper half adjacent to the cervix) and distal mouse vaginal smooth muscle strips were investigated. We hypothesised that nerve-mediated vaginal contractions arise through activity of cholinergic nerves. Nerve activation by bursts of electrical field stimulation (EFS) caused a primary transient contraction often accompanied by a secondary transient contraction, both larger in proximal than distal tissues (i.e. primary: 7-fold larger; secondary: 3-fold larger). Our hypothesis was supported as we found that cholinergic nerves mediated the primary transient contraction in both proximal and distal vaginal strips, as EFS responses were enhanced by neostigmine an anticholinesterase, massively inhibited by the competitive muscarinic receptor antagonist atropine and not affected by the non-selective a-adrenergic receptor antagonist phentolamine. Primary transient contractions were halved in amplitude by the L-type Ca2+ channel blocker nifedipine and markedly inhibited by the sarco-endoplasmic reticulum calcium ATPase (SERCA) inhibitor cyclopiazonic acid (CPA). Resultant secondary transient contractions were abolished by nifedipine. Notably, the selective a1-adrenergic receptor agonist phenylephrine caused tonic contracture in distal but not proximal strips. Low-frequency EFS often initiated recurrent transient contractions similar to those elicited by CCh. Immunohistochemical studies demonstrated innervation of the smooth muscle. Findings of enhanced proximal cholinergic nerve-induced transient contractions, evidence that maintained nerve stimulation could cause recurrent contractions and the finding of distal phenylephrine-mediated tonic contraction have implications on insemination.

This study assessed the¿effects of resveratrol, a polyphenol¿found in grapes and red wine¿on non-pregnant murine uteri under hypoxia. Resveratrol at 1, 3, 10, 30 and 100¿µM promoted uterine relaxation and decreased the amplitude and frequency of spontaneous uterine contractions. Assayed at 3, 10, 30¿µM, resveratrol inhibited the oxytocin-induced cumulative contractions reducing the maximum effect in a dose-dependent manner. In hypoxic uteri, resveratrol at 100¿µM restored the uterine contractions compromised by hypoxia. In addition, under hypoxia, resveratrol prevented the decrease in uterine contractions maintaining >75% of its contraction capability. The effects of resveratrol on uterine contractions under hypoxia were attenuated by tetraethylammonium (10¿mM) and almost abolished by glibenclamide (10¿µM). Our¿results show regenerative and protective effects of resveratrol in non-pregnant murine uteri under hypoxia and describes for the first time that these effects are mediated by blockade of ATP-sensitive potassium channels.

The mammalian brain is a mechanosensitive organ that responds to different mechanical forces ranging from intrinsic forces implicated in brain morphogenesis to extrinsic forces that can cause concussion and traumatic brain injury. However, little is known of the mechanosensors that transduce these forces. In this study we use cell-attached patch recording to measure single mechanically-gated (MG) channel currents and their affects on spike activity in identified neurons in neonatal mouse brain slices. We demonstrate that both neocortical and hippocampal pyramidal neurons express stretch-activated MG cation channels that are activated by suctions of ~25 mm Hg, have a single channel conductance for inward current of 50-70 pS and show weak selectivity for alkali metal cations (i.e., Na+<K+<Cs+). Significantly, single MG channel currents activated on the soma trigger spiking/action potentials in both neocortical and hippocampal pyramidal neurons. Not all neuron types studied here expressed MG channel currents. In particular, locus coeruleus and cerebellar Purkinje neurons showed no detectable MG channel activity. Moreover their robust rhythmic spike activity was resistant to mechanical modulation. Our observation that a single MG channel current can trigger spiking predicates the need for reassessment of the long held view that the impulse output of central neurons depends only upon their intrinsic voltage-gated channels and/or their integrated synaptic input.

Recent human imaging studies indicate that reduced blood flow through pial collateral vessels ('collateral failure') is associated with late infarct expansion despite stable arterial occlusion. The cause for 'collateral failure' is unknown. We recently showed that intracranial pressure (ICP) rises dramatically but transiently 24 hours after even minor experimental stroke. We hypothesized that ICP elevation would reduce collateral blood flow. First, we investigated the regulation of flow through collateral vessels and the penetrating arterioles arising from them during stroke reperfusion. Wistar rats were subjected to intraluminal middle cerebral artery (MCA) occlusion (MCAo). Individual pial collateral and associated penetrating arteriole blood flow was quantified using fluorescent microspheres. Baseline bidirectional flow changed to MCA-directed flow and increased by >450% immediately after MCAo. Collateral diameter changed minimally. Second, we determined the effect of ICP elevation on collateral and watershed penetrating arteriole flow. Intracranial pressure was artificially raised in stepwise increments during MCAo. The ICP increase was strongly correlated with collateral and penetrating arteriole flow reductions. Changes in collateral flow post-stroke appear to be primarily driven by the pressure drop across the collateral vessel, not vessel diameter. The ICP elevation reduces cerebral perfusion pressure and collateral flow, and is the possible explanation for 'collateral failure' in stroke-in-progression.

Conclusions/Significance: Cervical smooth muscle strips taken from mice in estrus, metestrus or late pregnancy were generally spontaneously active. Vaginal smooth muscle strips were normally quiescent but could be induced to exhibit phasic contractions independent on phase of the estrus cycle or late pregnancy. Spontaneous cervical or TEA-induced vaginal phasic contractions were not mediated by ICs or intracellular Ca2+ stores. Given that vaginal smooth muscle is normally quiescent then it is likely that increases in hormones such as oxytocin, as might occur through sexual stimulation, enhance the effectiveness of such pacemaking until phasic contractile activity emerges.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) causes sudden cardiac death due to mutations in cardiac ryanodine receptors (RyR2), calsequestrin, or calmodulin. Flecainide, a class I antiarrhythmic drug, inhibits Na⁺ and RyR2 channels and prevents CPVT. The purpose of this study is to identify inhibitory mechanisms of flecainide on RyR2. RyR2 were isolated from sheep heart, incorporated into lipid bilayers, and investigated by singlechannel recording under various activating conditions, including the presence of cytoplasmic ATP (2mM) and a range of cytoplasmic [Ca²⁺], [Mg²⁺], pH, and [caffeine]. Flecainide applied to either the cytoplasmic or luminal sides of the membrane inhibited RyR2 by two distinct modes: 1) a fast block consisting of brief substate and closed events with a mean duration of ~1 ms, and 2) a slow block consisting of closed events with a mean duration of ~1 second. Both inhibition modes were alleviated by increasing cytoplasmic pH from 7.4 to 9.5 but were unaffected by luminal pH. The slow block was potentiated in RyR2 channels that had relatively low open probability, whereas the fast block was unaffected by RyR2 activation. These results show that these two modes are independent mechanisms for RyR2 inhibition, both having a cytoplasmic site of action. The slow mode is a closed-channel block, whereas the fast mode blocks RyR2 in the open state. At diastolic cytoplasmic [Ca²⁺] (100 nM), flecainide possesses an additional inhibitory mechanism that reduces RyR2 burst duration. Hence, multiple modes of action underlie RyR2 inhibition by flecainide.