Genetic manipulation of cardiac Na+/Ca2+ exchange expression.
The Na+/Ca2+ exchanger (NCX) is the primary Ca2+ extrusion mechanism in cardiomyocytes. To further investigate the role of NCX in excitation-contraction coupling and Ca2+ homeostasis, we created murine models with altered expression levels of NCX. Homozygous overexpression of NCX resulted in mild cardiac hypertrophy. Decline of the Ca2+ transient and relaxation of contraction were increased and the reverse mode of NCX was augmented. Overexpression also led to a higher susceptibility to ischemia-reperfusion injury and to a greater ability of NCX to trigger Ca2+-induced Ca2+ release. Furthermore, an increase in peak L-type Ca2+ current was observed suggesting a direct influence of NCX on L-type Ca2+ current. Whereas global knockout of NCX led to prenatal death, a recently generated cardiac-specific NCX knockout mouse was viable with surprisingly normal contractile properties. Expression levels of other Ca2+-handling proteins were not altered. Ca2+ influx in these animals is limited by a decrease of peak L-type Ca2+ current. An alternative Ca2+ efflux mechanism, presumably the plasma membrane Ca2+-ATPase, is sufficient to maintain Ca2+-homeostasis in the NCX knockout mice.
Pott
Christian
C
Departments of Physiology and Medicine, The Cardiovascular Research Laboratories, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
Goldhaber
Joshua I
JI
Philipson
Kenneth D
KD
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D002118:Calcium