Contractile regulation by overexpressed ETA requires intact T tubules in adult rat ventricular myocytes.
Endothelin (ET)-1 regulates the contractility and growth of the heart by binding G protein-coupled receptors of the ET type A receptor (ET(A))/ET type B (ET(B)) receptor family. ET(A), the predominant ET-1 receptor subtype in myocardium, is thought to localize preferentially within cardiac T tubules, but the consequences of mislocalization are not fully understood. Here we examined the effects of the overexpression of ET(A) in conjunction with T-tubule loss in cultured adult rat ventricular myocytes. In adult myocytes cultured for 3 to 4 days, the normally robust positive inotropic effect (PIE) of ET-1 was lost in parallel with T-tubule degeneration and a decline in ET(A) protein levels. In these T tubule-compromised myocytes, an overexpression of ET(A) using an adenoviral vector did not rescue the responsiveness to ET-1, despite the robust expression in the surface sarcolemma. The inclusion of the actin polymerization inhibitor cytochalasin D (CD) during culture prevented gross morphological changes including a loss of T tubules and a rounding of intercalated discs, but CD alone did not rescue the responsiveness to ET-1 or prevent ET(A) downregulation. The rescue of a normal PIE in 3- to 4-day cultured myocytes required both an increased expression of ET(A) and intact T tubules (preserved with CD). Therefore, the activation of ET(A) localized in T tubules was associated with a strong PIE, whereas the activation of ET(A) in surface sarcolemma was not. The results provide insight into the pathological cardiac conditions in which ET(A) is upregulated and T-tubule morphology is altered.
Chung
Ka Young
KY
Molecular and Cellular Pharmacology Program, Department of Physiology, University of Wisconsin, 1300 University Avenue, Madison, WI 53706, USA.
Kang
Misuk
M
Walker
Jeffery W
JW
D000818:Animals; D021961:Cell Membrane Structures / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D048430:Cell Shape; D002478:Cells, Cultured; D015638:Cytochalasin D / Q000494:pharmacology; D019332:Endothelin-1 / Q000378:metabolism; D006352:Heart Ventricles / Q000378:metabolism; D006801:Humans; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044022:Receptor, Endothelin A / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D013997:Time Factors; D014161:Transduction, Genetic; D015854:Up-Regulation
D019332:Endothelin-1; D044022:Receptor, Endothelin A; D011993:Recombinant Fusion Proteins; D015638:Cytochalasin D