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Articles by S. M Schumacher
Total Records ( 2 ) for S. M Schumacher
  S. M Schumacher , D. P McEwen , L Zhang , K. L Arendt , K. M Van Genderen and J. R. Martens
 

Conventional antiarrhythmic drugs target the ion permeability of channels, but increasing evidence suggests that functional ion channel density can also be modified pharmacologically. Kv1.5 mediates the ultrarapid potassium current (IKur) that controls atrial action potential duration. Given the atrial-specific expression of Kv1.5 and its alterations in human atrial fibrillation, significant effort has been made to identify novel channel blockers. In this study, treatment of HL-1 atrial myocytes expressing Kv1.5-GFP with the class I antiarrhythmic agent quinidine resulted in a dose- and temperature-dependent internalization of Kv1.5, concomitant with channel block. This quinidine-induced channel internalization was confirmed in acutely dissociated neonatal myocytes. Channel internalization was subunit-dependent, activity-independent, stereospecific, and blocked by pharmacological disruption of the endocytic machinery. Pore block and channel internalization partially overlap in the structural requirements for drug binding. Surprisingly, quinidine-induced endocytosis was calcium-dependent and therefore unrecognized by previous biophysical studies focused on isolating channel–drug interactions. Importantly, whereas acute quinidine-induced internalization was reversible, chronic treatment led to channel degradation. Together, these data reveal a novel mechanism of antiarrhythmic drug action and highlight the possibility for new agents that selectively modulate the stability of channel protein in the membrane as an approach for treating cardiac arrhythmias.

  Y Wang , C Qian , A. J.M Roks , D Westermann , S. M Schumacher , F Escher , R. G Schoemaker , T. L Reudelhuber , W. H van Gilst , H. P Schultheiss , C Tschope and T. Walther
 

Background— Angiotensin (Ang)-(1-7) attenuates the development of heart failure. In addition to its local effects on cardiovascular tissue, Ang-(1-7) also stimulates bone marrow, which harbors cells that might complement the therapeutic effect of Ang-(1-7). We studied the effects of Ang-(1-7) either produced locally in the heart or subcutaneously injected during the development of heart failure induced by myocardial infarction (MI) and explored the role of cardiovascular progenitor cells in promoting the effects of this heptapeptide.

Methods and Results— Effects of Ang-(1-7) on bone marrow–derived mononuclear cells in rodents, particularly endothelial progenitor cells, were investigated in vitro and in vivo in rats, in mice deficient for the putative Ang-(1-7) receptor Mas, and in mice overexpressing Ang-(1-7) exclusively in the heart. Three weeks after MI induction through permanent coronary artery occlusion, effects of Ang-(1-7) either produced locally in the heart or injected into the subcutaneous space were investigated. Ang-(1-7) stimulated proliferation of endothelial progenitor cells isolated from sham or infarcted rodents. The stimulation was blunted by A779, a Mas receptor blocker, or by Mas deficiency. Infusion of Ang-(1-7) after MI increased the number of c-kit– and vascular endothelial growth factor–positive cells in infarcted hearts, inhibited cardiac hypertrophy, and improved cardiac function 3 weeks after MI, whereas cardiomyocyte-derived Ang-(1-7) had no effect.

Conclusions— Our data suggest circulating rather than cardiac Ang-(1-7) to be beneficial after MI. This beneficial effect correlates with a stimulation of cardiac progenitor cells in vitro and in vivo. This characterizes the heptapeptide as a promising new tool in stimulating cardiovascular regeneration under pathophysiological conditions.

 
 
 
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