Abstract
Background: Diastolic Ca2+ waves lead to arrhythmias by inducing delayed after-depolarisations. Waves are initiated when sarcoplasmic reticulum (SR) Ca2+ content reaches a threshold level. Phosphodiesterase-5 inhibitor sildenafil is antiarrhythmic in small mammalian ischaemia models via an unknown mechanism.
Determine effects of sildenafil on propensity to waves and ventricular arrhythmias in the large mammal.
Methods and results: Sheep ventricular myocytes were voltage-clamped and intracellular Ca2+ measured (Fura-2). Cells were paced at 0.5 Hz and waves induced with 10-15 mM Ca2+. Upon regular waving, sildenafil (1μM) was applied. To determine ‘threshold’ SR content, caffeine (10mM) was added immediately following a wave, and both wave and caffeine-induced INCX integrated.
Increasing external Ca2+ elevated SR content and induced waves. Sildenafil abolished waves in 12/22 cells. In cells where sildenafil terminated waves, SR content was reduced below threshold. Underlying this effect, sildenafil reduced rate constant of SERCA, transiently increased sarcolemmal efflux via NCX tail current, and reduced sarcolemmal entry by decreasing both ICa-L and background influx. Protective effects of sildenafil on waves were abolished in cells pre-incubated with the PKG-inhibitor, KT5823. Sildenafil suppressed ventricular ectopy and episodes of torsades de pointes in vivo in a sheep model of LQT2.
Conclusion: Sildenafil suppresses waves via a PKG-dependent mechanism. This is mediated by a reduction in SR content via reduced SERCA, which itself is caused by reduced SR uptake and decreased sarcolemmal Ca entry via ICa-L and background influx. These findings highlight novel antiarrhythmic properties of PDE5 inhibition and translate to suppression of triggered arrhythmias in vivo.
Funding: British Heart Foundation
Determine effects of sildenafil on propensity to waves and ventricular arrhythmias in the large mammal.
Methods and results: Sheep ventricular myocytes were voltage-clamped and intracellular Ca2+ measured (Fura-2). Cells were paced at 0.5 Hz and waves induced with 10-15 mM Ca2+. Upon regular waving, sildenafil (1μM) was applied. To determine ‘threshold’ SR content, caffeine (10mM) was added immediately following a wave, and both wave and caffeine-induced INCX integrated.
Increasing external Ca2+ elevated SR content and induced waves. Sildenafil abolished waves in 12/22 cells. In cells where sildenafil terminated waves, SR content was reduced below threshold. Underlying this effect, sildenafil reduced rate constant of SERCA, transiently increased sarcolemmal efflux via NCX tail current, and reduced sarcolemmal entry by decreasing both ICa-L and background influx. Protective effects of sildenafil on waves were abolished in cells pre-incubated with the PKG-inhibitor, KT5823. Sildenafil suppressed ventricular ectopy and episodes of torsades de pointes in vivo in a sheep model of LQT2.
Conclusion: Sildenafil suppresses waves via a PKG-dependent mechanism. This is mediated by a reduction in SR content via reduced SERCA, which itself is caused by reduced SR uptake and decreased sarcolemmal Ca entry via ICa-L and background influx. These findings highlight novel antiarrhythmic properties of PDE5 inhibition and translate to suppression of triggered arrhythmias in vivo.
Funding: British Heart Foundation
| Original language | English |
|---|---|
| Pages (from-to) | 37 |
| Number of pages | 1 |
| Journal | Journal of molecular and cellular cardiology |
| Volume | 120 |
| Publication status | Published - Jul 2018 |