Cardiac myocyte alternans in intact heart: Influence of cell–cell coupling and β-adrenergic stimulation

Abstract

Background Cardiac alternans are proarrhythmic and mechanistically link cardiac mechanical dysfunction and sudden cardiac death. Beat-to-beat alternans occur when beats with large Ca2+ transients and long action potential duration (APD) alternate with the converse. APD alternans are typically driven by Ca2+ alternans and sarcoplasmic reticulum (SR) Ca2+ release alternans. But the effect of intercellular communication via gap junctions (GJ) on alternans in intact heart remains unknown. Objective We assessed the effects of cell-to-cell coupling on local alternans in intact Langen-dorff-perfused mouse hearts, measuring single myocyte [Ca2+] alternans synchronization among neighboring cells, and effects of β-adrenergic receptor (β-AR) activation and reduced GJ coupling. Methods and Results Mouse hearts (C57BL/6) were retrogradely perfused and loaded with Fluo-8 AM to record cardiac myocyte [Ca2+] in situ with confocal microscopy. Single cell resolution allowed analysis of alternans within the intact organ during alternans induction. Carbenoxolone (25 μM), a GJ inhibitor, significantly increased the occurrence and amplitude of alternans in single cells within the intact heart. Alternans were concordant between neighboring cells throughout the field of view, except transiently during onset. β-AR stimulation only reduced Ca2+ alternans in tissue that had reduced GJ coupling, matching effects seen in isolated myocytes. Conclusions Ca2+ alternans among neighboring myocytes is predominantly concordant, likely because of electrical coupling between cells. Consistent with this, partial GJ uncoupling increased propensity and amplitude of Ca2+ alternans, and made them more sensitive to reversal by β-AR activation, as in isolated myocytes. Electrical coupling between myocytes may thus limit the alternans initiation, but also allow alternans to be more stable once established.

Dedifferentiation, Proliferation, and Redifferentiation of Adult Mammalian Cardiomyocytes After Ischemic Injury

“…We confirmed that the NRVM Ca 2+ that influences ACM redifferentiation travels into ACM via gap junctions. 42 Ischemia impaired gap junction function and blocked Ca 2+ induced ACM redifferentiation. An ischemia-resistant mutant of Cx43 with stable phosphorylation at serine residues 325/328/330 rescued these effects.…”

β-Adrenergic receptor stimulation inhibits proarrhythmic alternans in postinfarction border zone cardiomyocytes: a computational analysis

“…Cellular mechanisms of alternans have been investigated in numerous experimental and computational studies ( 14 , 15 , 18 , 31 , 43 , 46 , 62 ), which have highlighted a complex interplay between different Ca 2+ handling processes ( 57 ). In particular, a sarcoplasmic reticulum (SR) Ca 2+ release-reuptake mismatch ( 8 , 26 , 62 ) or refractoriness of the type 2 ryanodine receptor (RyR2) channel, responsible for SR Ca 2+ release ( 41 ), have been proposed to contribute to Ca 2+ transient (CaT) alternans formation ( Fig.…”

“…Recent human studies have also shown that lack of reinnervation after MI predicts future occurrence of SCD ( 2 , 13 ). Similarly, β-AR agonists have been used to suppress repolarization alternans in some studies ( 14 , 18 , 26 , 56 ) but increased alternans in others ( 36 ).…”

Calcium-Dependent Arrhythmogenic Foci Created by Weakly Coupled Myocytes in the Failing Heart

“…32 Figure 4A–B shows that CBX reduced FRAP dramatically in CTL-SY myocytes, reaching only the steady state level seen in HF-AS myocytes (Figure 4B–C). We also tried to promote coupling in HF hearts using rotigaptide (ZP123, 50nM), which has been reported to enhance gap junctional conductance.…”

“…In both the Ca-V m coupling study and gap junction FRAP experiments, the gap junction uncoupler carbenoxolone (CBX; Sigma-Aldrich, St. Louis, MO; 25μmol/L) 32 or I k1 blocker BaCl 2 (Sigma-Aldrich, St. Louis, MO; 5 μmol/L) 37 were delivered by aortic perfusion into hearts. The gap junction modifier rotigaptide (ZP123; 50nmol/L), which is reported to increase gap junctional conductance, 38,39 was perfused into HF hearts.…”