title: Reduction in density of transverse tubules and L-type Ca(2+) channels in canine tachycardia-induced heart failure.
abstract: OBJECTIVE
  Persistent supraventricular tachycardia leads to the development of a dilated cardiomyopathy with impairment of excitation-contraction (EC) coupling. Since the initial trigger for EC coupling in ventricular muscle is the influx of Ca(2+) through L-type Ca(2+) channels (I(Ca)) in the transverse tubules (T-tubules), we determined if the density of the T-tubule system and L-type Ca(2+) channels change in canine tachycardia pacing-induced cardiomyopathy.
  
  
  METHODS
  Confocal imaging of isolated ventricular myocytes stained with the membrane dye Di-8-ANEPPS was used to image the T-tubule system, and standard whole-cell patch clamp techniques were used to measure I(Ca) and intramembrane charge movement.
  
  
  RESULTS
  A complex staining pattern of interconnected tubules including prominent transverse components spaced every approximately 1.6 microm was present in control ventricular myocytes, but failing cells demonstrated a far less regular T-tubule system with a relative loss of T-tubules. In confocal optical slices, the average % of the total cell area staining for T-tubules decreased from 11.5+/-0.4 in control to 8.7+/-0.4% in failing cells (P<0.001). Whole-cell patch clamp studies revealed that I(Ca) density was unchanged. Since whole-cell I(Ca) is due to both the number of channels as well as the functional properties of those channels, we measured intramembrane charge movement as an assay for changes in channel number. The saturating amount of charge that moves due to gating of L-type Ca(2+) channels, Q(on,max), was decreased from 6.5+/-0.6 in control to 2.8+/-0.3 fC/pF in failing myocytes (P<0.001).
  
  
  CONCLUSIONS
  Cellular remodeling in heart failure results in decreased density of T-tubules and L-type Ca(2+) channels, which contribute to abnormal EC coupling.
authors.affiliation: Department of Physiology, University of Wisconsin, Madison, Wisconsin 53792, USA.
authors.forename: J
authors.initials: J
authors.lastname: He
authors.forename: M W
authors.initials: MW
authors.lastname: Conklin
authors.forename: J D
authors.initials: JD
authors.lastname: Foell
authors.forename: M R
authors.initials: MR
authors.lastname: Wolff
authors.forename: R A
authors.initials: RA
authors.lastname: Haworth
authors.forename: R
authors.initials: R
authors.lastname: Coronado
authors.forename: T J
authors.initials: TJ
authors.lastname: Kamp
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D048429:Cell Size; D004095:Dihydropyridines / Q000494:pharmacology; D004285:Dogs; D006333:Heart Failure / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D007091:Image Processing, Computer-Assisted; D015640:Ion Channel Gating / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D018613:Microscopy, Confocal; D023421:Models, Animal; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure*; D018408:Patch-Clamp Techniques; D013610:Tachycardia / Q000150:complications* / Q000473:pathology / Q000503:physiopathology
chemical_list: D000318:Adrenergic beta-Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004095:Dihydropyridines; C045796:SAN 202791; D007545:Isoproterenol