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  • 1
    ISSN: 1423-0127
    Keywords: Antiarrhythmic agents ; Potassium channels ; Voltage clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The slow delayed rectifier potassium current (IKs) is unique in its slow activation and deactivation kinetics. It is important during cardiac repolarization, especially when the heart rate is fast. We compared the effects of quinidine, procainamide, sotalol, and amidarone on IKs and correlated the findings with the clinical reverse use-dependent effects of potassium channel blockers. Human minK RNA was obtained by reverse transcription-polymerase chain reaction using explanted human heart. The RNA was injected into Xenopus oocytes for heterologous expression of IKs. A two-electrode voltage clamp technique was performed to investigate the IKs. We demonstrated that quinidine, sotalol and procainamide had no effects on IKs up to a concentration of 300 µM while amiodarone inhibited IKs in a concentration-dependent manner starting from 10 µM. The inhibition by amiodarone was state-dependent with gradual unblocking after depolarization. The degree of inhibition was 53% immediately after depolarization and 19% at the end of a 5-second depolarization. IKs is 30 times more sensitive to amiodarone than to quinidine, sotalol, and procainamide. Quinidine, sotalol and procainamide have reverse use-dependent effects while amiodarone does not. This is compatible with the hypothesis that no inhibition of IKs at clinical concentrations contributes to the clinical reverse use-dependent effects.
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  • 2
    ISSN: 0730-2312
    Keywords: M-line proteins ; titin ; expression ; antibody perturbation ; immunocytochemistry ; cardiomyocyte ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: A rat polyclonal anti-M-line protein antiserum and three mouse monoclonal anti-titin antibodies (E2, F3, and A12) were used to study the spatiotemporal relationship between M-line proteins and titin during myofibril assembly in cultured chicken cardiomyocytes by immunofluorescence microscopy. In day 2 cultures, M-line proteins and titin were detected as punctate staining in most cardiomyocytes, which possessed many nonstriated fibrils. At a late stage (day 3 cultures), M-line proteins were incorporated into dot-like structures along nonstriated fibrils, while titin staining was continuous on these structures. As development progressed, M-line proteins were registered in periodic pattern in the mid-A band. In cardiomyocytes from day 5 cultures, the titin bands were separated by an unstained region, and achieved their adult doublet pattern. Thus, the organization of titin in the sarcomere appears to occur later than that of M-line proteins in the M-line. Our morphological data indicate that the early registration of M-line proteins in primitive myofibrils may guide titin filament alignment via interaction between M-line proteins and titin. In order to investigate the role of M-line proteins in the assembly of titin filaments, anti-M-line protein or anti-titin antibodies were introduced into cultured cardiomyocytes by electroporation to functionally bind the respective proteins, and the profile of myofibril assembly was examined. Cardiomyocytes from day 2-3 cultures with incorporated anti-M-line protein antibodies became shrunk, and exhibited defective myofibrillar assembly, as shown by the failure of titin to assemble into a typical sarcomeric pattern. Incorporation of anti-titin antibody E2, which recognizes the M-line end domain of titin, resulted in the failure of M-line proteins organized into the M-line structure, as shown by random, sporadic staining with anti-M-line protein antibody. These studies confirm the essential role of M-line proteins in the organization of titin filaments in the sarcomere and that the interaction between titin and M-line proteins is crucial to the formation of the M-line structure. J. Cell. Biochem. 71:82-95, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
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  • 3
    ISSN: 0730-2312
    Keywords: rho A ; C3 exoenzyme ; focal adhesion ; costamere ; myofibrillogenesis ; cardiomyocyte ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The aim of this study was to provide morphological evidence for the presence of rho A protein in developing cardiomyocytes and to investigate its possible role in myofibrillogenesis. Immunostaining with a monoclonal anti-rho antibody gave a diffuse pattern in the cytosol of cultured cardiomyocytes. Introduction of C3 exoenzyme into the cells by electroporation was used to inactivate rho A protein by ADP-ribosylation. An immunostaining with anti-vinculin, anti-talin, and anti-integrin antibodies showed the focal adhesions in electroporation control cardiomyocytes to be evenly distributed in the ventral sarcolemma; the costameric structure was also detected using these antibodies. In contrast, in C3 exoenzyme treated cells, focal adhesions were disassembled and costamere were absent; in addition, β-actin-positive, non-striated fibrils were lost and assembly of M-protein, titin, and α-actinin into myofibrils was poor, as shown by diffuse and filamentous staining pattern. C3 exoenzyme treatment had a less marked effect on mature cardiomyocytes than on immature cells; in this case, cells became distorted and few myofibrils were seen. The intensity of anti-phosphotyrosine antibody staining of the focal adhesion was also decreased or diffuse in C3 exoenzyme-treated cardiomyocytes, suggesting dephosphorylation of focal adhesion components. We therefore conclude that small G protein rho A plays an important role in myofibril assembly in cardiomyocytes. J. Cell. Biochem. 66:43-53, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
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