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Research has been conducted on the human cardiac troponin I mutations. The effect of these mutations and the adjacent N-terminal serine residue phosphorylation on the wild-type human cardiac troponin I and the mutated proteins has been investigated and the results are reported.

The sequential glycolytic reactions catalyzed by aldolase, triosephosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase are compartmentalized in skeletal muscle triads. This finding was obtained from experiments on ATP synthesis and glycolytic activity of the enzymes. The results suggest that endogenously synthesized ATP is utilized in part by structure associated protein kinases and phosphatases in phsophorylation of protens involved in the excitation-contraction coupling of skeletal muscle.

Abstract: Objective: Mutations in the cardiac ryanodine receptor (RYR2) gene have been reported to cause arrhythmogenic right ventricular cardiomyopathy (ARVC). The molecular mechanisms by which genetic modifications lead to ARVC are still not well understood. Methods: ARVC patients were screened for mutations in the RYR2 gene by denaturing HPLC and DNA sequencing. Single channel measurements were carried out with RyR2 channels purified from explanted hearts of ARVC patients. Results: None of the published RYR2 mutations were found in our ARVC-cohort. However, we identified two single nucleotide polymorphisms (SNPs) in exon 37 of the human RYR2 gene which lead to the amino acid exchanges G1885E and G1886S, respectively. Both SNPs together were found exclusively in 3 out of 85 ARVC patients in a composite heterozygous fashion (genotype T4). This genotype was associated with ARVC (p <0.05) but not with dilated cardiomyopathy (DCM, 79 patients) or none-failing controls (463 blood donors). However, either one of the two SNPs were identified in further 7 ARVC patients, in 11 DCM patients, and in 64 blood donors. The SNP leading to G1886S may create a protein kinase C phosphorylation site in the human RyR2. Single channel recordings at pCa4.3 revealed four conductance states for the RyR2 of genotype T4 and a single open state for the wild type RyR2. At pCa7.7, the lowest subconductance state of the RyR2 channel of genotype T4 persisted with a greatly enhanced open probability indicating a leaky channel. Conclusion: The RyR2 channel leak under diastolic conditions could cause SR-Ca2+ depletion, concomitantly arrhythmogenesis and heart failure in a subgroup of ARVC patients of genotype T4. A change in the RyR2 subunit composition due to the combined expression of both SNPs alters the behaviour of the tetrameric channel complex. [Copyright &y& Elsevier]

: BackgroundMyocardial recovery is observed in some end-stage heart failure patients after mechanical circulatory support. The sarcoplasmic reticulum Ca2+–adenosine triphosphatase (Ca2+-ATPase) activity is down-regulated in failing myocardium and contributes to heart failure–associated contraction/relaxation abnormalities. Regulation of Ca2+-ATPase after mechanical support was shown to be heterogenous. Thus, we analyzed Ca2+-ATPase activity and protein expression in the paired myocardial samples of 21 patients supported by ventricular assist devices to identify factors that influence restoration of the Ca2+-transient after ventricular assist device support.: MethodsWe measured Ca2+-ATPase activity using a reduced nicotinamide-adenine dinucleotide–coupled reaction, determined sarcoplasmic reticulum Ca2+-dependent ATPase protein using Western blotting, and determined 4-hydroxyproline using amino-acid analysis.: ResultsThe mean Ca2+-ATPase activity decreased at assist-device implantation and slightly increased at transplantation, but remained significantly lower than in non-failing donor hearts. However, individual responses were heterogeneous. Patients with older age, increased left ventricular diameter, and increased 4-hydroxyproline content showed down-regulation of Ca2+-ATPase activity, whereas we found up-regulation in patients with low values for these parameters after assist-device support.: ConclusionsSarcoplasmic reticulum Ca2+-ATPase activity, which influences the myocardial Ca2+-transient, generally is not restored to normal values in assist-device–supported hearts, but depends on a combined score of the left ventricular end-diastolic diameter, degree of ventricular fibrosis, and age of the patient at the time of assist-device implantation. [Copyright &y& Elsevier]