Donald M Bers

..Our results suggest that CaMKII-dependent phosphorylation of RyR2 is involved in enhanced SR diastolic Ca leak and reduced SR Ca load in HF, and may thus contribute to arrhythmias and contractile dysfunction in HF...

..Furthermore, spatial microdomains within the cell are important in localizing the molecular players that orchestrate cardiac function...

..In heart failure, there are significant alterations in how myocyte Ca is regulated, and these alterations are critical in dictating both contractile dysfunction and certain cardiac arrhythmias that are characteristic of heart failure...

..The lower expression level of more phosphorylated PLM in HF may explain the above dichotomy. Thus, altered Ca(2+) and Na(+) handling contributes to altered contractile function and arrhythmogenesis in HF...

..These complexes, and their relative independence emphasizes the importance of thinking about other aspects of very local molecular signaling, analogous to the local control of SR Ca-release at the heart of current (E-C) coupling theory...

..In this way cells can use Ca signaling in multiple ways that function in spatially and temporally distinct manners...

..We conclude that NaCaX contributes in major ways to both contractile dysfunction (by reducing SR Ca) and increased propensity for triggered arrhythmias (by increasing I(ti) and DADs)...

..Thus, the balance of Na+ fluxes in heart cells may be complex, but myocyte Na+ regulation is functionally important and merits focused attention as in this issue...

..Importantly, although such diverse Ca-dependent regulations occur simultaneously in a cell, the cell can distinguish distinct signals by local Ca or protein complexes and differential Ca signal integration...

..These issues are discussed in both normal physiological and pathophysiological contexts...

..Complementary approaches useful in studying localized changes in Ca2+ and other second messengers (such as cyclic adenosine monophosphate) are also discussed...

..This study brings some new answers, but also raises additional new questions that will require further investigation...

..However, evidence from subcellular and expression systems shows the process to be dynamic, and our observations confirm this to be the case in intact cardiac cells as well...

..Phospholemman is an important regulator of NKA function (decreasing [Na(+)](i) affinity unless it is phosphorylated). Here we discuss the interplay between Ca(2+) and Na(+) in myocytes from normal and failing hearts...

..This may directly contribute to the development and/or maintenance of HF...

..Recent evidence shows that phosphorylation of the NKA-associated small transmembrane protein phospholemman (PLM) mediates beta-adrenergic-induced NKA stimulation...

..We conclude that the acute inotropic effects of DIG, ACS and OUA (and the effects on RyRs) depend on the presence of Na(+) and a functional NCX in ferret and cat myocytes (rather than alternate Na(+)-independent mechanisms)...

..At very positive V(m), reduced i(Ca) must explain reduced SR Ca2+ release...

..Thus, the beta-AR hyporesponsiveness in human HF is mediated in large part by NO (or related congeners) produced within cardiac myocytes via NOS2...

..Moreover, this may explain the enhanced SR diastolic Ca2+ leak and certain triggered arrhythmias seen in heart failure...

..Intracellular sodium concentration ([Na(+)](i)) modulates cardiac contractile and electrical activity through Na/Ca exchange (NCX). Upregulation of NCX in heart failure (HF) may magnify the functional impact of altered [Na(+)](i)...

..However, we also found that sparks explain approximately half of J(leak). Our strategy unmasks the presence of a subresolution (i.e., nonspark) release of potential physiological relevance...

..5), respectively), and (3) PDBu and ISO combine to activate NKA in wild-type to the level found in the PLM knockout mouse...

..Thus SR-targeted CaMKII inhibition can directly inhibit the activation of SR Ca(2+) uptake, SR Ca(2+) release and I(Ca) by CaMKII, effects which have all been implicated in triggered arrhythmias...

..We conclude that CaMKIIdeltaC overexpression causes acute modulation of excitation-contraction coupling, which contributes to heart failure...

..CONCLUSIONS: These results show that Ca entry through NCX may limit systolic dysfunction due to reduced sarcoplasmic reticulum Ca stores in HF but could contribute to slow decay of the [Ca]i transient and to diastolic dysfunction...

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..These new biosensors allow studying InsP3 dynamics at high temporal and spatial resolution that will be powerful in under-standing InsP3 signaling in intact cells...

..Thus, myocytes can distinguish simultaneous local and global Ca2+ signals involved in contractile activation from those targeting gene expression...

..In this way, diastolic [Ca2+]SR alternans can enhance frequency-induced Ca2+ alternans, even if they initiate by other means...

..Our results indicate that there are dynamic changes in free Ca-CaM levels (a phasic component tracking [Ca]i) as well as system memory that integrates the [Ca]i signals (a tonic component)...

..This suggests that INa effects on excitation-contraction coupling (via outward INCX) are minimal and limited to early during the action potential. However, local Delta[Na+]sm during INa may be 60 times higher than bulk Delta[Na+]i...

..Truncation of the transmembrane domain by L39Stop mutation prevents anchoring of the protein in the membrane, greatly reducing PLB binding to itself or its regulatory target, SERCA...

..Eventually, these events terminate by luminal Ca-independent mechanisms, such as inactivation, adaptation, or stochastic attrition...

..The increased amount of SR Ca(2+) release normally seen with ISO depends primarily on increased I(Ca) trigger and SR Ca(2+) load, whereas faster release kinetics may be the main result of RyR phosphorylation...

..However, such effects are likely to be either minor (vs. other PKA actions on myocyte Ca handling) or indirect, such as secondary effects dependent on altered local [Ca](i) and [Na](i)...

..We conclude that PLM phosphorylation at either Ser63 or Ser68 is both necessary and sufficient for completely relieving the PLM-induced NKA inhibition...

..Moreover, the data provide compelling evidence that elevated intra-SR [Ca2+] increases RyR gating independent of cytosolic [Ca2+] (which was clamped)...

..Treatment with ISO plus KN93 completely abolished this effect. The evidence suggests the ISO-dependent increase in SCaW activity in both healthy and failing myocytes is CaMKII-dependent, implicating CaMKII in arrhythmogenesis...

..This approach could enhance contractile function in failing hearts of various etiologies, even here where reduced SERCA activity is not the main dysfunction...

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..Phosphatase 1 appears to be the main phosphatase dephosphorylating S2808/S2814, but phosphatase 2a may also dephosphorylate S2814. RyR phosphorylation is complex, but important in understanding RyR functional modulation...

..We conclude that phospholemman and Na/K-pump are in very close proximity (FRET occurs) and that phospholemman phosphorylation alters the interaction of Na/K-pump and phospholemman...

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..This rapid luminal communication may maintain homogeneously high luminal [Ca(2+)], ensuring a robust and uniform driving force for local Ca(2+) release events from either SR or NucEn...

..We found that SparkMaster provides a reliable, easy to use, and fast way of analyzing Ca sparks in a wide variety of experimental conditions...

..The functional density of NKA-alpha2 is approximately 4.5 times higher in the T-tubules vs. ESL, whereas NKA-alpha1 is almost uniformly distributed between the TT and ESL...

..These findings place stringent novel constraints on how excitation-contraction coupling works in heart and also reveal a Ca2+ store reserve that could in principle be a therapeutic target to enhance cardiac function in heart failure...

..We hypothesize that this increased Ca influx can explain the slowed decay and impaired relaxation of failing human ventricular myocytes...

..So reduced Na/K-ATPase expression in HF may be functionally offset by lower inhibition by PLM (because of reduced PLM expression and higher PLM phosphorylation)...

..We conclude that PLM modulates the NKA function in a manner similar to the way phospholamban affects the related SR Ca-ATPase (inhibition of transport substrate affinity, that is relieved by phosphorylation)...

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..We conclude that low total SR Ca2+ content in HF, and reduced SR Ca2+ release, is attributable to reduced [Ca2+]SR, not to alterations in SR volume or Ca2+ buffering capacity...

..Our simulations suggest that NCX current is outward for less than approximately 10 ms at the beginning of the action potential...

..The contribution of the computer modeler to their respective biological fields will be more successful and enduring if modelers devote sufficient time to implement their equations into a model with user-friendly characteristics...

..We conclude that long APD and slower [Ca(2+)](i) decline lead to cumulative inactivation limiting I(Ca) at high heart rates and might contribute to the negative FFR in HF, independent of altered Ca(2+) channel properties...

..Bound CaM is relatively concentrated at Z-lines at rest but translocates significantly to the nucleus upon elevation of [Ca2+]i, which may influence activation of different targets and cellular functions...

..We conclude that phosphorylation of PLM increases its oligomerization into tetramers, decreases its binding to NKA, and alters the structures of both the tetramer and NKA regulatory complex...

..These results show that RyRs are the main, but not sole contributor to SR Ca²(+) leak. RyR-mediated leak occurs in part as Ca²(+) sparks, but there is clearly RyR-mediated but Ca²(+) sparks independent leak...

..The early rise in [Ca(2+)](sm) causes I(NCX) to be inward for the majority of the AP. Thus, little Ca(2+) influx via NCX is expected under physiological conditions, but this can differ among species and in pathophysiological conditions...

..We conclude that chronic PMA or ET-1 exposure in cultured NRVMs causes altered functional expression of cardiac ion currents, which mimic electrophysiological changes seen in whole animal and human hypertrophy and heart failure...

..We conclude that FDAR results mainly from CaMKII-dependent stimulation of SR Ca transport, but does not require phospholamban...

..Hsp20 renders this protection through its C-terminal extension protein domain, while this part of the protein is not involved in the Hsp20 ability to increase both calcium transients and cell contraction...

..I(pump) integrals and [Na](i) decline were used to estimate intracellular Na buffering, which is slight (1.39 +/- 0.09)...

..We conclude that resting [Na+]i is higher in rat than in rabbit, that this is caused by higher resting Na+ influx in rat and that a higher Na+,K+-ATPase pumping rate in rat is a consequence of the higher [Na+]i...

..A simple diffusion model indicated that such gradients require a Na diffusion coefficient of 10-12 microm(2)/s, significantly lower than in aqueous solutions...

..Many cases could be prevented if they were anticipated through means of a better awareness among the medical community, new therapies based on early genetic screening, or corrected by countershock...

..Better recognition of primary pulmonary hypertension can produce better treatment by comprehensive therapists...

..Here we review the classical role of Ca in E-C coupling and extend this view to the role of the Ca-dependent proteins CaM and CaMKII in modulating E-C coupling and their contribution to E-T coupling...

..Furthermore, two CPVT-inducing CASQ2 mutations, which cause mechanistically different defects in CASQ2 and RyR2 function, lead to increased diastolic SR Ca release events and exhibit a similar CPVT disease phenotype...

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..Therapeutic approaches to the treatment of HF will need to balance increasing SR Ca load with the arrhythmogenic effects of SR Ca overload that involve activation of I(ti) carried by Na/Ca exchanger...

..These changes can explain the defective Ca2+ transients of the failing human ventricular myocyte...

..Collectively, these data suggest that HRC may be an integral regulatory protein involved in cardiac muscle SR Ca uptake and Ca homeostasis...

..We conclude that RyR regulation may play a role in preventing arrhythmias in healthy myocytes but that the same regulation may have the opposite effect in chronic heart failure...

..Thus, beta(2)-AR stimulation is arrhythmogenic in HF, mediated by SR Ca overload-induced spontaneous SR Ca release and aftercontractions...

..This study demonstrates that inhibition of SR CaMKII activity at the LSR results in alterations in cardiac contractility and Ca2+ handling in TG hearts...

..Thus, reliable SR Ca(2+) release termination depends on tight RyR regulation by [Ca(2+)](SR)...

..This ICa modulation may partly compensate for the loss in SERCA2a responsiveness and thereby partially normalize beta-adrenergic inotropy in DM phospholamban mice...

..This inotropic response appears to be independent of autocrine/paracrine AT1 or ET(A) receptor activation, but mediated through stretch-induced activation of NHE and reverse mode NCX...

..We investigated the effects of different levels of SERCA1a expression on contractility and Ca2+ cycling. We tested whether increased SERCA1a expression levels enhance myocyte contractility in a gene-dose-dependent manner...

..In mice, enhanced CaMKIIdelta(C) activity predisposed to VT. Thus, CaMKII-dependent regulation of Na(+) channel function may contribute to arrhythmogenesis in HF...

..We conclude that increased diastolic SR Ca2+ leak in HF may contribute to reductions in SR Ca2+ content, but changes in NCX in this HF model have more impact on [Ca2+]SRT...

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..The results suggest that beta-AR stimulation enhances diastolic SR Ca leak in a manner that is (1) CaMKII dependent, (2) not protein kinase A dependent, and 3) not dependent on bulk [Ca](i)...

..Junctin is a major transmembrane protein in cardiac junctional sarcoplasmic reticulum, which forms a quaternary complex with the ryanodine receptor (Ca(2+) release channel), triadin, and calsequestrin...

..We conclude that this model is more robust than many previously existing models and reproduces many experimental results using parameters based largely on experimental measurements in myocytes...

..Our method is illustrated by a simple model of the diadic cleft of a cardiac half-sarcomere...

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..This provides a useful initial framework to consider pathways by which CaMKII may contribute to arrhythmogenesis...

..The subcellular distribution of these isoforms in T-tubule and surface sarcolemmal (SSL) membranes and their regulation by cAMP-dependent protein kinase (PKA) is unclear...

..We conclude that this is attributable to concomitant enhancement of fractional SR Ca2+ release in CaMKIIdeltaC myocytes (ie, CaMKII-dependent enhancement of RyR Ca2+ sensitivity during diastole and systole) and increased ICa...

..This work will greatly increase fundamental understanding of key cardiac Ca transport systems in the intact cellular environment under physiological conditions. ..