Biology subjects

Cameron, B. A.

Publications and source records attributed to Cameron, B. A..

5 recordsLinked to original sources

bioRxiv2024

Disturbed repolarisation-relaxation coupling during acute ischaemia permits systolic mechano-arrhythmogenesis.

BackgroundThe hearts mechanical state feeds back to its electrical activity, potentially contributing to arrhythmias. Mechano-arrhythmogenesis has been mechanistically explained during electrical diastole, when cardiomyocytes are at their resting membrane potential. During electrical systole, cardiomyocytes are refractory right from the onset of depolarisation, while during repolarisation they appear to be protected from mechano-arrhythmogenesis by near-simultaneous restoration of resting membrane potential and cytosolic calcium concentration ([Ca2+]i): repolarisation-relaxation coupling (RRC). Yet, systolic mechano-arrhythmogenesis has been reported in ischaemic myocardium, with unclear underlying mechanisms. We hypothesise that ischaemia-induced alteration of RRC gives rise to a vulnerable period for mechano-arrhythmogenesis. MethodsAcute left-ventricular (LV) regional ischaemia was induced by coronary artery ligation in Langendorff-perfused rabbit hearts, with mechanical load controlled by an intraventricular balloon. Mechanical activity was assessed by echocardiography and arrhythmia incidence by electrocardiogram. Single LV cardiomyocytes were exposed to simulated ischaemia or pinacidil (ATP-sensitive potassium channel opener). Stretch was applied in diastole or late systole using carbon fibres. Stretch characteristics and arrhythmia incidence were assessed by sarcomere length measurement. In both models, RRC was assessed by simultaneous voltage-[Ca2+]i fluorescence imaging and mechano-arrhythmogenesis mechanisms were pharmacologically tested. ResultsIn whole heart, acute regional ischaemia leads to systolic stretch and disturbed RRC at the ischaemic border. These electro-mechanical changes were associated with waves of arrhythmias, which were reduced by mechanical unloading, electro-mechanical uncoupling, or buffering of [Ca2+]i. In LV cardiomyocytes, physiological RRC is associated with a low incidence of systolic mechano-arrhythmogenesis, while a vulnerable period emerged by prolonged RRC during ischaemia. The increase in systolic mechano-arrhythmogenesis was reduced by restoring RRC, chelating [Ca2+]i, blocking mechano-sensitive transient receptor potential kinase ankyrin 1 channels (TRPA1), or buffering reactive oxygen species (ROS) levels. ConclusionProlonged RRC allows for systolic mechano-arrhythmogenesis in acute ischaemia, involving contributions of elevated [Ca2+]i, TRPA1 activity, and ROS, which represent potential anti-arrhythmic targets. GRAPHICAL ABSTRACT LEGENDRole of disturbed repolarisation-relaxation coupling (RRC), transient receptor potential kinase ankyrin 1 (TRPA1) channels, cytosolic calcium concentration ([Ca2+]i), and reactive oxygen species (ROS) in ventricular systolic mechano-arrhythmogenesis. Schematic of the proposed mechanisms underlying the TRPA1- and Ca2+-mediated increase in systolic mechano-arrhythmogenesis with disturbed RRC. AITC, Allyl isothiocyanate (TRPA1 channel activator); AP, action potential; BAPTA ([Ca2+]i buffer); CaT, Ca2+ transient; DNT, dantrolene (ryanodine receptor stabiliser); DPI, diphenyleneiodonium (ROS production blocker); GLIB, glibenclamide (KATP channel blocker); HC-300031 (TRPA1 channel blocker); KATP, ATP-sensitive potassium channel; NAC, N-acetyl-L-cysteine (ROS chelator); NCX, sodium-Ca2+ exchanger; PIN, pinacidil (KATP channel activator); ROS, reactive oxygen species; SI, simulated ischaemia; STP, streptomycin (non-specific mechano-sensitive ion channel blocker).

physiology↗

bioRxiv2024

Repolarisation-relaxation dyscoupling and TRPA1 activation permit systolic mechano-arrhythmogenesis

BackgroundThe hearts mechanical state feeds back to its electrical activity, potentially contributing to arrhythmias (mechano-arrhythmogenesis, MAR). MAR has been mechanistically explained during electrical diastole, when cardiomyocytes are at their resting membrane potential. Conversely, during electrical systole, cardiomyocytes appear to be protected from MAR, even as membrane potential and cytosolic calcium concentration ([Ca2+]i) are simultaneously restored to resting levels during repolarisation (repolarisation-relaxation coupling, RRC). Yet, systolic MAR has been reported in ischaemic myocardium, with unclear underlying mechanisms. MethodsRabbit left ventricular cardiomyocytes were electrically paced and exposed to a simulated ischaemia solution (including hyperkalaemia, acidosis, and block of oxidative phosphorylation) or pinacidil (to simulate ischaemia-induced opening of ATP-sensitive potassium [KATP] channels), with or without glibenclamide (to block KATP channels). RRC was assessed by simultaneous measurement of membrane voltage and [Ca2+]i dynamics with fluorescence imaging. Acute stretch at increasing magnitudes was applied using carbon fibres, with stretch timed to diastole or late systole. Stretch mechanics and the incidence of MAR was assessed by video-based measurement of sarcomere length. Mechanisms contributing to MAR were assessed by buffering [Ca2+]i (BAPTA-AM), stabilising ryanodine receptors (dantrolene), non-specifically blocking mechano-sensitive channels (streptomycin), activating (AITC) or blocking (HC-030031) transient receptor potential kinase ankyrin 1 channels (TRPA1), or chelating (NAC) or blocking production of (DPI) reactive oxygen species (ROS). ResultsIt was reconfirmed that MAR during physiological RRC is rare, while ischaemia- or pharmacologically-induced RRC dyscoupling generates a vulnerable period for systolic MAR. This systolic MAR depends on TRPA1, [Ca2+]i, and ROS, which contribute to stretch-induced excitation and arrhythmia sustenance. An increase in systolic MAR can be prevented by mitigating RRC dyscoupling with KATP channel block, or by blocking TRPA1, buffering [Ca2+]i, or reducing ROS. ConclusionRRC dyscoupling may be arrhythmogenic in ischaemia and other pathologies associated with systolic MAR, and TRPA1 may be a novel anti-arrhythmic target.

physiology↗

bioRxiv2023

Age-related structural and functional changes of the intracardiac nervous system

BackgroundAlthough aging is known to be associated with an increased incidence of both atrial and ventricular arrhythmias, there is limited knowledge about how Schwann cells (SC) and the intracardiac nervous system (iCNS) remodel with age. Here we investigate the differences in cardiac SC, parasympathetic nerve fibers, and muscarinic acetylcholine receptor M2 (M2R) expression in young and old mice. Additionally, we examine age-related changes in cardiac responses to sympathomimetic and parasympathomimetic drugs. Methods and ResultsLower SC density, lower SC proliferation and fewer parasympathetic nerve fibers were observed in cardiac and, as a control sciatic nerves from old (20-24 months) compared to young mice (2-3 months). In old mice, CSPG4 was increased in sciatic but not cardiac nerves. Expression of M2R was lower in ventricular myocardium and ventricular conduction system from old mice compared to young mice, while no significant difference was seen in M2R expression in sino-atrial or atrio-ventricular node pacemaker tissue. Heart rate was slower and PQ intervals were longer in Langendorff-perfused hearts from old mice. Ventricular tachycardia and fibrillation were more frequently observed in response to carbachol administration in hearts from old mice versus those from young mice. ConclusionsOn the background of reduced presence of SC and parasympathetic nerve fibers, and of lower M2R expression in ventricular cardiomyocytes and conduction system of aged hearts, the propensity of ventricular arrhythmogenesis upon parasympathomimetic drug application is increased. Whether this is caused by an increase in heterogeneity of iCNS structure and function remains to be elucidated. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=192 HEIGHT=200 SRC="FIGDIR/small/568538v1_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@11dbccdorg.highwire.dtl.DTLVardef@1563d75org.highwire.dtl.DTLVardef@dcda58org.highwire.dtl.DTLVardef@182e598_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2021

Mechano-arrhythmogenicity is enhanced during late repolarisation in ischemia and driven by a TRPA1-, calcium-, and reactive oxygen species-dependent mechanism

BackgroundCardiac dyskinesis in regional ischemia results in arrhythmias through mechanically-induced changes in electrophysiology ( mechano-arrhythmogenicity) that involve ischemic alterations in voltage-calcium (Ca2+) dynamics, creating a vulnerable period (VP) in late repolarisation. ObjectiveTo determine cellular mechanisms of mechano-arrhythmogenicity in ischemia and define the importance of the VP. Methods and ResultsVoltage-Ca2+ dynamics were simultaneously monitored in rabbit ventricular myocytes by dual-fluorescence imaging to assess the VP in control and simulated ischemia (SI). The VP was longer in SI than in control (146{+/-}7 vs 54{+/-}8ms; p<0.0001) and was reduced by blocking KATP channels with glibenclamide (109{+/-}6ms; p<0.0001). Cells were rapidly stretched (10-18% increase in sarcomere length over 110-170ms) with carbon fibres during diastole or the VP. Mechano-arrhythmogenicity, associated with stretch and release in the VP, was greater in SI than control (7 vs 1% of stretches induced arrhythmias; p<0.005) but was similar in diastole. Arrhythmias during the VP were more complex than in diastole (100 vs 69% had sustained activity; p<0.05). In the VP, incidence was reduced with glibenclamide (2%; p<0.05), by chelating intracellular Ca2+ (BAPTA; 2%; p<0.05), blocking mechano-sensitive TRPA1 (HC-030031; 1%; p<0.005), or by scavenging (NAC; 1%; p<0.005) or blocking reactive oxygen species (ROS) production (DPI; 2%; p<0.05). Ratiometric Ca2+ imaging revealed that SI increased diastolic Ca2{+/-} (+9{+/-}1%, p<0.0001), which was not prevented by HC-030031 or NAC. ConclusionIn ischemia, mechano-arrhythmogenicity is enhanced specifically during the VP and is mediated by ROS, TRPA1, and Ca2+.

physiology↗

bioRxiv2020

TRPA1 channels are a source of calcium-driven cardiac mechano-arrhythmogenicity

SUMMARY PARAGRAPHMaintenance of cardiac function involves a regulatory loop in which electrical excitation causes the heart to contract through excitation-contraction coupling (ECC),1 and the mechanical state of the heart directly affects its electrical activity through mechano-electric coupling (MEC).2 However, in pathological states such as acute ischaemia that alter early or late electro-mechanical coordination (i.e., disturbances in ECC or repolarisation-relaxation coupling, RRC), MEC may contribute to the initiation and / or sustenance of arrhythmias (mechano-arrhythmogenesis).3 The molecular identity of specific factor(s) underlying mechano-arrhythmogenesis in acute ischaemia, however, remain undefined.4 By rapid stretch of rabbit single left ventricular cardiomyocytes, we show that upon ATP-sensitive potassium channel-induced alterations of RRC, overall vulnerability to mechano-arrhythmogenesis is increased, with mechano-sensitive5-11 transient receptor potential kinase ankyrin 1 (TRPA1) channels12 acting as the molecular driver through a Ca2+-mediated mechanism. Specifically, TRPA1 activation drives stretch-induced excitation and creates a substrate for self-sustained arrhythmias, which are maintained by increased cytosolic free Ca2+ concentration ([Ca2+]i) and spontaneous [Ca2+]i oscillations. This TRPA1-dependent mechano-arrhythmogenesis involves microtubules, and can be prevented by block of TRPA1 or buffering of [Ca2+]i. Thus, in cardiac pathologies with disturbed RRC dynamics and / or augmented TRPA1 activity, TRPA1 may represent an anti-arrhythmic target with untapped therapeutic potential.13-17

physiology↗