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(Circulation Research. 2008;103:1109.)
© 2008 American Heart Association, Inc.

Cellular Biology

Ca²⁺ Influx Through T- and L-Type Ca²⁺ Channels Have Different Effects on Myocyte Contractility and Induce Unique Cardiac Phenotypes

Naser Jaleel^*, Hiroyuki Nakayama^*, Xiongwen Chen^*, Hajime Kubo^*, Scott MacDonnell, Hongyu Zhang, Remus Berretta, Jeffrey Robbins, Leanne Cribbs, Jeffery D. Molkentin, Steven R. Houser

From the Department of Physiology (N.J., X.C., H.K., S.M., H.Z., R.B., S.R.H.), Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, Pa; Department of Pediatrics (H.N., J.R., J.D.M.), Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Ohio; and Department of Physiology, Cardiovascular Institute (L.C.), Loyola University Medical Center, Maywood, Ill.

Correspondence to Dr Steven R. Houser, 3420 N Broad St, Philadelphia, PA 19140. E-mail steven.houser{at}temple.edu

T-type Ca²⁺ channels (TTCCs) are expressed in the developing heart, are not present in the adult ventricle, and are reexpressed in cardiac diseases involving cardiac dysfunction and premature, arrhythmogenic death. The goal of this study was to determine the functional role of increased Ca²⁺ influx through reexpressed TTCCs in the adult heart. A mouse line with cardiac-specific, conditional expression of the 1G-TTCC was used to increase Ca²⁺ influx through TTCCs. 1G hearts had mild increases in contractility but no cardiac histopathology or premature death. This contrasts with the pathological phenotype of a previously studied mouse with increased Ca²⁺ influx through the L-type Ca²⁺ channel (LTCC) secondary to overexpression of its β2a subunit. Although 1G and β2a myocytes had similar increases in Ca²⁺ influx, 1G myocytes had smaller increases in contraction magnitude, and, unlike β2a myocytes, there were no increases in sarcoplasmic reticulum Ca²⁺ loading. Ca²⁺ influx through TTCCs also did not induce normal sarcoplasmic reticulum Ca²⁺ release. 1G myocytes had changes in LTCC, SERCA2a, and phospholamban abundance, which appear to be adaptations that help maintain Ca²⁺ homeostasis. Immunostaining suggested that the majority of 1G-TTCCs were on the surface membrane. Osmotic shock, which selectively eliminates T-tubules, induced a greater reduction in L- versus TTCC currents. These studies suggest that T- and LTCCs are in different portions of the sarcolemma (surface membrane versus T-tubules) and that Ca²⁺ influx through these channels induce different effects on myocyte contractility and lead to distinct cardiac phenotypes.

Key Words: T-type Ca²⁺ channels • myocyte death • EC coupling

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