Basal Spontaneous Firing of Rabbit Sinoatrial Node Cells Is Regulated by Dual Activation of PDEs (Phosphodiesterases) 3 and 4. (June 2018)

• Record Type: Journal Article
• Authors: Vinogradova, Tatiana M.; Sirenko, Syevda; Lukyanenko, Yevgeniya O.; Yang, Dongmei; Tarasov, Kirill V.; Lyashkov, Alexey E.; Varghese, Nevin J.; Li, Yue; Chakir, Khalid; Ziman, Bruce; Lakatta, Edward G.
• Is Part Of: Circulation. Volume 11:Number 6(2018)
• Publication Date: 2018-06
• Subjects: calcium -- calcium channel -- phosphodiesterase -- phospholamban -- sarcoplasmic reticulum -- sinoatrial node; Arrhythmia -- Periodicals; Heart -- Electric properties -- Periodicals; 616.128
• DOI: 10.1161/CIRCEP.117.005896
• Languages: English
• ISSNs: 1941-3149

Abstract

Abstract : Background: Spontaneous firing of sinoatrial node cells (SANCs) is regulated by cAMP-mediated, PKA (protein kinase A)-dependent (cAMP/PKA) local subsarcolemmal Ca 2+ releases (LCRs) from RyRs (ryanodine receptors). LCRs occur during diastolic depolarization and activate an inward Na + /Ca 2+ exchange current that accelerates diastolic depolarization rate prompting the next action potential. PDEs (phosphodiesterases) regulate cAMP-mediated signaling; PDE3/PDE4 represent major PDE activities in SANC, but how they modulate LCRs and basal spontaneous SANC firing remains unknown. Methods: Real-time polymerase chain reaction, Western blot, immunostaining, cellular perforated patch clamping, and confocal microscopy were used to elucidate mechanisms of PDE-dependent regulation of cardiac pacemaking. Results: PDE3A, PDE4B, and PDE4D were the major PDE subtypes expressed in rabbit SANC, and PDE3A was colocalized with α-actinin, PDE4D, SERCA (sarcoplasmic reticulum Ca 2+ ATP-ase), and PLB (phospholamban) in Z-lines. Inhibition of PDE3 (cilostamide) or PDE4 (rolipram) alone increased spontaneous SANC firing by ≈20% ( P <0.05) and ≈5% ( P >0.05), respectively, but concurrent PDE3+PDE4 inhibition increased spontaneous firing by ≈45% ( P <0.01), indicating synergistic effect. Inhibition of PDE3 or PDE4 alone increased L-type Ca 2+ current (ICa, L ) by ≈60% ( P <0.01) or ≈5% ( P >0.05), respectively, and PLB phosphorylation by ≈20% ( P >0.05) each, but dual PDE3+PDE4 inhibition increased ICa, L by ≈100% ( P <0.01) and PLB phosphorylation by ≈110% ( P <0.05). Dual PDE3+PDE4 inhibition increased the LCR number and size ( P <0.01) and reduced the SR (sarcoplasmic reticulum) Ca 2+ refilling time ( P <0.01) and the LCR period (time from action potential–induced Ca 2+ transient to subsequent LCR; P <0.01), leading to decrease in spontaneous SANC cycle length ( P <0.01). When RyRs were disabled by ryanodine and LCRs ceased, dual PDE3+PDE4 inhibition failed to increase spontaneous SANC firing. Conclusions: Basal cardiac pacemaker function is regulated by concurrent PDE3+PDE4 activation which operates in a synergistic manner via decrease in cAMP/PKA phosphorylation, suppression of LCR parameters, and prolongation of the LCR period and spontaneous SANC cycle length. Abstract : Supplemental Digital Content is available in the text.