Cardiac dysfunction is a well-known consequence of diabetes,with sustained hyperglycaemia leading to the development of a cardiomyopathy that is independent of cardiovascular disease or hypertension.Animal models of d...Cardiac dysfunction is a well-known consequence of diabetes,with sustained hyperglycaemia leading to the development of a cardiomyopathy that is independent of cardiovascular disease or hypertension.Animal models of diabetes are commonly used to study the pathophysiology of diabetic cardiomyopathy,with the hope that increased knowledge will lead ultimately to better therapeutic strategies being developed.At physiological temperature,left ventricular trabeculae isolated from the streptozotocin rat model of type 1 diabetes showed decreased stress and prolonged relaxation,but with no evidence that decreased contractility was a result of altered myocardial Ca2+handling.Although sarcoplasmic reticulum(SR)Ca2+reuptake appeared slower in diabetic trabeculae,it was offset by an increase in actionpotential duration,thereby maintaining SR Ca2+content and favouring increased contraction force.Frequency analysis of t-tubule distribution by confocal imaging of ventricular tissue labeled with wheat germ agglutinin or ryanodine receptor antibodies showed a reduced T-power for diabetic tissue,but the differences were minor in comparison to other models of heart failure.The contractile dysfunction appeared to be the result of disrupted F-actin in conjunction with the increased typeⅠcollagen,with decreased myofilament Ca2+sensitivity contributing to the slowed relaxation.展开更多
Calcium is a crucial element for striated muscle function. As such, myoplasmic free Ca2+ concentration is delicately regulated through the concerted action of multiple Ca2+ pathways that relay excitation of the plasma...Calcium is a crucial element for striated muscle function. As such, myoplasmic free Ca2+ concentration is delicately regulated through the concerted action of multiple Ca2+ pathways that relay excitation of the plasma membrane to the intracellular contractile machinery. In skeletal muscle, one of these major Ca2+ pathways is Ca2+ release from intracellular Ca2+ stores through type-1 ryanodine receptor/Ca2+ release channels (RyR1), which positions RyR1 in a strategic cross point to regulate Ca2+ homeostasis. This major Ca2+ traff ic point appears to be highly sensitive to the intracellular environment, which senses through a plethora of chemical and protein-protein interactions. Among these modulators, perhaps one of the most elusive is Triadin, a musclespecif ic protein that is involved in many crucial aspect of muscle function. This family of proteins mediates complex interactions with various Ca2+ modulators and seems poised to be a relevant modulator of Ca2+ signaling in cardiac and skeletal muscles. The purpose of this review is to examine the most recent evidence and current understanding of the role of Triadin in muscle function, in general, with particular emphasis on its contribution to Ca2+ homeostasis.展开更多
Ryanodine receptors are ion channels that allow for the release of Ca2+ from the endoplasmic or sarcoplasmic reticulum.They are expressed in many different cell types but are best known for their predominance in skele...Ryanodine receptors are ion channels that allow for the release of Ca2+ from the endoplasmic or sarcoplasmic reticulum.They are expressed in many different cell types but are best known for their predominance in skeletal and cardiac myocytes,where they are directly involved in excitation-contraction coupling.With molecular weights exceeding 2 MDa,Ryanodine Receptors are the largest ion channels known to date and present major challenges for structural biology.Since their discovery in the 1980s,significant progress has been made in understanding their behaviour through multiple structural methods.Cryo-electron microscopy reconstructions of intact channels depict a mushroom-shaped structure with a large cytoplasmic region that pre-sents many binding sites for regulatory molecules.This region undergoes significant motions during opening and closing of the channel,demonstrating that the Ryanodine Receptor is a bona fide allosteric protein.High-resolution structures through X-ray crystallography and NMR currently cover～11% of the entire protein.The combination of high-and low-resolution methods allows us to build pseudo-atomic models.Here we present an overview of the electron microscopy,NMR,and crystallographic analyses of this membrane protein giant.展开更多
The elementary Ca^2＋ release events, Ca2＋ sparks, has been found for a quarter of century. However, the molecular regulation of the spark generator, the ryanodine receptor （RyR） on the sarcoplasmic reticulum, rema...The elementary Ca^2＋ release events, Ca2＋ sparks, has been found for a quarter of century. However, the molecular regulation of the spark generator, the ryanodine receptor （RyR） on the sarcoplasmic reticulum, remains obscure. Although each subunit of the RyR homotetramer has a site for FKS06-binding protein （FKBP）, the role of FKBPs in modifying RyR Ca^2＋ sparks has been debated for long. One of the reasons behind the controversy is that most previous studies detect spontaneous sparks, where the mixture with out-of-focus events and local wavelets prevents an accurate characterization of Ca^2＋ sparks. In the pre- sent study, we detected Ca^2＋ sparks triggered by single L-type Ca^2＋ channels （LCCs） under loose-seal patch clamp conditions in FKS06-treated or FKBPI2.6 knockout cardiomyocytes. We found that FKBP dissociation both by FKS06 and by rapamycin decreased the Ca^2＋ spark amplitude in ventricular cardiomyocytes. This change was neither due to decreased releasable Ca^2＋ in the sarcoplasmic reticulum, nor explained by changed RyR sensitivity. Actually FKS06 increased the LCC-RyR coupling probability and curtailed the latency for an LCC to trigger a RyR Ca^2＋ spark. FKBP12.6 knockout had similar effects as FKS06/rapamycin treatment, indicating that the decreased spark amplitude was attributable to the dissociation of FKBP12.6 rather than FKBP12. We also explained how decreased amplitude of spontaneous sparks after FKBP dissociation sometimes appears to be increased or unchanged due to inappropriate data processing. Our results provided firm evidence that without the inter-RyR coordination by functional FKBP12.6, the RyR recruitment during a Ca^2＋ spark would be compromised despite the sensitization of individual RyRs.展开更多
基金Supported by The Health Research Council of New Zealand
文摘Cardiac dysfunction is a well-known consequence of diabetes,with sustained hyperglycaemia leading to the development of a cardiomyopathy that is independent of cardiovascular disease or hypertension.Animal models of diabetes are commonly used to study the pathophysiology of diabetic cardiomyopathy,with the hope that increased knowledge will lead ultimately to better therapeutic strategies being developed.At physiological temperature,left ventricular trabeculae isolated from the streptozotocin rat model of type 1 diabetes showed decreased stress and prolonged relaxation,but with no evidence that decreased contractility was a result of altered myocardial Ca2+handling.Although sarcoplasmic reticulum(SR)Ca2+reuptake appeared slower in diabetic trabeculae,it was offset by an increase in actionpotential duration,thereby maintaining SR Ca2+content and favouring increased contraction force.Frequency analysis of t-tubule distribution by confocal imaging of ventricular tissue labeled with wheat germ agglutinin or ryanodine receptor antibodies showed a reduced T-power for diabetic tissue,but the differences were minor in comparison to other models of heart failure.The contractile dysfunction appeared to be the result of disrupted F-actin in conjunction with the increased typeⅠcollagen,with decreased myofilament Ca2+sensitivity contributing to the slowed relaxation.
文摘Calcium is a crucial element for striated muscle function. As such, myoplasmic free Ca2+ concentration is delicately regulated through the concerted action of multiple Ca2+ pathways that relay excitation of the plasma membrane to the intracellular contractile machinery. In skeletal muscle, one of these major Ca2+ pathways is Ca2+ release from intracellular Ca2+ stores through type-1 ryanodine receptor/Ca2+ release channels (RyR1), which positions RyR1 in a strategic cross point to regulate Ca2+ homeostasis. This major Ca2+ traff ic point appears to be highly sensitive to the intracellular environment, which senses through a plethora of chemical and protein-protein interactions. Among these modulators, perhaps one of the most elusive is Triadin, a musclespecif ic protein that is involved in many crucial aspect of muscle function. This family of proteins mediates complex interactions with various Ca2+ modulators and seems poised to be a relevant modulator of Ca2+ signaling in cardiac and skeletal muscles. The purpose of this review is to examine the most recent evidence and current understanding of the role of Triadin in muscle function, in general, with particular emphasis on its contribution to Ca2+ homeostasis.
基金funded by the CIHR(operating grant 84350)the Heart and Stroke Foundation of Canadaa CIHR new investigator and a Michael Smith Foundation for Health Research Scholar
文摘Ryanodine receptors are ion channels that allow for the release of Ca2+ from the endoplasmic or sarcoplasmic reticulum.They are expressed in many different cell types but are best known for their predominance in skeletal and cardiac myocytes,where they are directly involved in excitation-contraction coupling.With molecular weights exceeding 2 MDa,Ryanodine Receptors are the largest ion channels known to date and present major challenges for structural biology.Since their discovery in the 1980s,significant progress has been made in understanding their behaviour through multiple structural methods.Cryo-electron microscopy reconstructions of intact channels depict a mushroom-shaped structure with a large cytoplasmic region that pre-sents many binding sites for regulatory molecules.This region undergoes significant motions during opening and closing of the channel,demonstrating that the Ryanodine Receptor is a bona fide allosteric protein.High-resolution structures through X-ray crystallography and NMR currently cover～11% of the entire protein.The combination of high-and low-resolution methods allows us to build pseudo-atomic models.Here we present an overview of the electron microscopy,NMR,and crystallographic analyses of this membrane protein giant.
基金supported by the National Research and Development Program of China (2016YFA0500401)National Natural Science Foundation of China (31630035, 31571486, 81370203, 81461148026, 31271228 and 31327901)the Project of Beijing Municipal Science and Technology Commission (Z141100000214006)
文摘The elementary Ca^2＋ release events, Ca2＋ sparks, has been found for a quarter of century. However, the molecular regulation of the spark generator, the ryanodine receptor （RyR） on the sarcoplasmic reticulum, remains obscure. Although each subunit of the RyR homotetramer has a site for FKS06-binding protein （FKBP）, the role of FKBPs in modifying RyR Ca^2＋ sparks has been debated for long. One of the reasons behind the controversy is that most previous studies detect spontaneous sparks, where the mixture with out-of-focus events and local wavelets prevents an accurate characterization of Ca^2＋ sparks. In the pre- sent study, we detected Ca^2＋ sparks triggered by single L-type Ca^2＋ channels （LCCs） under loose-seal patch clamp conditions in FKS06-treated or FKBPI2.6 knockout cardiomyocytes. We found that FKBP dissociation both by FKS06 and by rapamycin decreased the Ca^2＋ spark amplitude in ventricular cardiomyocytes. This change was neither due to decreased releasable Ca^2＋ in the sarcoplasmic reticulum, nor explained by changed RyR sensitivity. Actually FKS06 increased the LCC-RyR coupling probability and curtailed the latency for an LCC to trigger a RyR Ca^2＋ spark. FKBP12.6 knockout had similar effects as FKS06/rapamycin treatment, indicating that the decreased spark amplitude was attributable to the dissociation of FKBP12.6 rather than FKBP12. We also explained how decreased amplitude of spontaneous sparks after FKBP dissociation sometimes appears to be increased or unchanged due to inappropriate data processing. Our results provided firm evidence that without the inter-RyR coordination by functional FKBP12.6, the RyR recruitment during a Ca^2＋ spark would be compromised despite the sensitization of individual RyRs.
