Depletion of T-tubules and specific subcellular changes in sarcolemmal proteins in tachycardia-induced heart failure.
OBJECTIVE
The T-tubule membrane network is integrally involved in excitation-contraction coupling in ventricular myocytes. Ventricular myocytes from canine hearts with tachycardia-induced dilated cardiomyopathy exhibit a decrease in accessible T-tubules to the membrane-impermeant dye, di8-ANNEPs. The present study investigated the mechanism of loss of T-tubule staining and examined for changes in the subcellular distribution of membrane proteins essential for excitation-contraction coupling.


METHODS
Isolated ventricular myocytes from canine hearts with and without tachycardia-induced heart failure were studied using fluorescence confocal microscopy and membrane fractionation techniques using a variety of markers specific for sarcolemmal and sarcoplasmic reticulum proteins.


RESULTS
Probes for surface glycoproteins, Na/K ATPase, Na/Ca exchanger and Ca(v)1.2 demonstrated a prominent but heterogeneous reduction in T-tubule labeling in both intact and permeabilised failing myocytes, indicating a true depletion of T-tubules and associated membrane proteins. Membrane fractionation studies showed reductions in L-type Ca(2+) channels and beta-adrenergic receptors but increased levels of Na/Ca exchanger protein in both surface sarcolemma and T-tubular sarcolemma-enriched fractions; however, the membrane fraction enriched in junctional complexes of sarcolemma and junctional sarcoplasmic reticulum demonstrated no significant changes in the density of any sarcolemmal protein or sarcoplasmic reticulum protein assayed.


CONCLUSIONS
Failing canine ventricular myocytes exhibit prominent depletion of T-tubules and changes in the density of a variety of proteins in both surface and T-tubular sarcolemma but with preservation of the protein composition of junctional complexes. This subcellular remodeling contributes to abnormal excitation-contraction coupling in heart failure.
Balijepalli
Ravi C
RC
Department of Medicine, University of Wisconsin, Madison, WI 53792, USA.
Lokuta
Andrew J
AJ
Maertz
Nathan A
NA
Buck
Jennifer M
JM
Haworth
Robert A
RA
Valdivia
Hector H
HH
Kamp
Timothy J
TJ
D000818:Animals; D020746:Calcium Channels, L-Type / Q000032:analysis; D000252:Calcium-Transporting ATPases / Q000032:analysis; D002155:Calsequestrin / Q000032:analysis; D002304:Cardiac Pacing, Artificial; D002458:Cell Fractionation; D002478:Cells, Cultured; D004285:Dogs; D004594:Electrophysiology; D006333:Heart Failure / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000032:analysis; D017275:Isradipine / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009124:Muscle Proteins / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000648:ultrastructure*; D011485:Protein Binding; D011943:Receptors, Adrenergic, beta / Q000032:analysis; D012433:Ryanodine / Q000378:metabolism; D012508:Sarcolemma / Q000378:metabolism / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger / Q000032:analysis; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis
D020746:Calcium Channels, L-Type; D002155:Calsequestrin; D018398:Homeodomain Proteins; D009124:Muscle Proteins; D011943:Receptors, Adrenergic, beta; D019831:Sodium-Calcium Exchanger; D012433:Ryanodine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D017275:Isradipine