Biology subjects

Madders, G. W.

Publications and source records attributed to Madders, G. W..

3 recordsLinked to original sources

bioRxiv2026

Cardiac microtubules mediate transverse (t)-tubule growth and homeostasis

Transverse (t)-tubules enable rapid, synchronous Ca release required for efficient cardiac contraction by bringing L-type Ca channels into close apposition with ryanodine receptors. In heart failure with reduced ejection fraction (HFrEF), t-tubule disorganisation and loss occur alongside cardiac microtubule remodelling, contributing to impaired Ca handling and contractile dysfunction. Despite their canonical function in contraction, how t-tubules develop is unknown. Microtubules support delivery of L-type Ca channels to t-tubules via Amphiphysin-II/BIN1, yet whether microtubules directly regulate t-tubule formation and maintenance is unclear. Here, we investigated a role for microtubules in t-tubule development and homeostasis. Neonatal rat ventricular myocytes (NRVMs), which lack endogenous t-tubules, were used as a reductionist model in which BIN1 overexpression induces nascent membrane tubules. Microtubule depolymerisation with nocodazole before BIN1 overexpression impaired BIN1-driven tubule formation, reducing tubule density and length. Dynein inhibition with EHNA produced similar effects, indicating a requirement for microtubule-based motor activity during tubule elongation. Knockdown of the microtubule +TIP tracking protein CLIP-170 also reduced BIN1-driven tubule density, implicating BIN1-CLIP-170-dependent microtubule capture in tubule initiation. Microtubules were also required to maintain existing tubules. In NRVMs with established BIN1-driven tubules, microtubule depolymerisation, microtubule stabilisation or dynein inhibition each reduced tubule density and length. Consistent with this, acute microtubule depolymerisation or stabilisation disrupted native t-tubule networks in isolated adult sheep left atrial myocytes. Together, these findings identify cardiac microtubules as active regulators of t-tubule architecture. We propose that BIN1-dependent tubule formation requires CLIP-170-mediated microtubule plus-end capture and dynein-dependent elongation, while ongoing microtubule dynamics are necessary to preserve mature t-tubule structure.

physiology↗

bioRxiv2024

Acute sildenafil administration reduces susceptibility to induced atrial fibrillation in sheep

BackgroundSildenafil is a PDE5 inhibitor with a very good safety profile and animal models suggest it may be beneficial in the treatment of heart failure and ventricular fibrillation. Sildenafil has also been associated with a reduced incidence of atrial fibrillation (AF) in a retrospective observational study. We have therefore sought to determine whether sildenafil has a direct effect on atrial electrophysiology and resultant AF burden. MethodsInvasive electrophysiological studies were performed in 12 anaesthetised healthy adult female Welsh mountain sheep. Pacing protocols were performed in the right atrium before and after administration of an acute 10 mg intravenous bolus of sildenafil and the burden of AF assessed. ResultsSildenafil profoundly reduced the vulnerability to AF, decreasing AF duration (112.2 {+/-} 73.5 s vs. 3.3 {+/-} 1.4 s), the number of burst pacing inductions causing AF (90 % vs 70 %) and the complexity of AF. The antiarrhythmic effects of sildenafil were determined to be resultant of prolongation of both the atrial effective refractory period (146.9 {+/-} 7.2 ms vs 166.2 {+/-} 32.5 ms) and the atrial excitation wavelength (12.9 {+/-} 0.07 cm vs 15.0 {+/-} 0.07 cm) and resulted in a shallower restitution curve, reflected in a decreased magnitude of monophasic action potential alternans (0.09 {+/-} 0.001 mV vs 0.05 {+/-} 0.10 mV). ConclusionsIn the subjectively healthy atria of a highly translational model a strong antiarrhythmic effect upon acute sildenafil application was observed suggestive of a potential clinical benefit in AF.

physiology↗

bioRxiv2018

PDE5 inhibition improves symptom-free survival and restores transverse tubule loss and catecholamine responsiveness in heart failure

Heart failure is characterized by poor survival, a loss of catecholamine reserve and cellular structural remodeling in the form of disorganization and loss of the transverse tubule network. Indeed, survival rates for heart failure are worse than many common cancers and have not improved over time. Tadalafil is a clinically relevant drug that blocks phosphodiesterase 5 with high specificity and is used to treat erectile dysfunction. Using a sheep model of advanced heart failure, we show that tadalafil treatment results in a marked improvement in symptom-free survival, reverses transverse tubule loss and restore cardiac myocyte systolic calcium transient amplitude and the hearts chronotropic and contractile response to catecholamines. These effects are independent of changes in myocardial cGMP content and are associated with upregulation of both monomeric and dimerized forms of protein kinase G and of the cGMP hydrolyzing phosphodiesterase 2 and 3. We propose that the molecular switch for the loss of transverse tubules in heart failure and their restoration following tadalafil treatment involves the BAR domain protein Amphiphysin II (BIN1) and the restoration of catecholamine sensitivity is through reductions in G-protein receptor kinase 2, protein phosphatase 1 and protein phosphatase 2A abundance following phosphodiesterase 5 inhibition.

physiology↗