Reduced synchrony of Ca2+ release with loss of T-tubules-a comparison to Ca2+ release in human failing cardiomyocytes.
OBJECTIVE
During cardiac excitation-contraction coupling, Ca2+ release from the sarcoplasmic reticulum (SR) occurs at the junctional complex with the T-tubules, containing the L-type Ca2+ channels. A partial loss of T-tubules has been described in myocytes from failing canine and human hearts. We examined how graded reduction of T-tubule density would affect the synchrony of Ca2+ release.


METHODS
Adult pig ventricular myocytes were isolated and cultured for 24 and 72 h. T-tubules, visualized with di-8-ANEPPS, and [Ca2+]i transients (Fluo-3) were recorded during confocal line scan imaging.


RESULTS
Cultured cardiomyocytes exhibited a progressive reduction in T-tubule density. [Ca2+]i transients showed small areas of delayed Ca2+ release which gradually increased in number and size with loss of T-tubules. Local [Ca2+]i transients in the delayed regions were reduced. Due to these changes, loss of T-tubules resulted in an overall slowing of the rise of [Ca2+] along the entire line scan and transient magnitude tended to be reduced, but there was no change in SR Ca2+ content. Human myocytes isolated from failing hearts had a T-tubule density comparable to that of freshly isolated pig myocytes. The size, but not the number, of delayed release areas tended to be larger. The overall rate of rise of [Ca2+]i was significantly faster than in pig myocytes with low T-tubule density.


CONCLUSIONS
Loss of T-tubules reduces the synchrony of SR Ca2+ release. This could contribute to reduced efficiency of excitation-contraction coupling in heart failure, though dyssynchrony in human failing cells appears to be modest.
Louch
William E
WE
Laboratory of Experimental Cardiology, University of Leuven, Campus Gasthuisberg O/N 7th floor, Herestraat 49, B-3000 Leuven, Belgium.
Bito
Virginie
V
Heinzel
Frank R
FR
Macianskiene
Regina
R
Vanhaecke
Johan
J
Flameng
Willem
W
Mubagwa
Kanigula
K
Sipido
Karin R
KR
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004594:Electrophysiology; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D018613:Microscopy, Confocal; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000648:ultrastructure*; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure*; D013552:Swine
D002118:Calcium