μ-Calpain-mediated deregulation of cardiac, brain, and kidney NCX1 splice variants.
μ-Calpain is a Ca(2+)-activated protease abundant in mammalian tissues. Here, we examined the effects of μ-calpain on three alternatively spliced variants of NCX1 using the giant, excised patch technique. Membrane patches from Xenopus oocytes expressing either heart (NCX1.1), kidney (NCX1.3), or brain (NCX1.4) variants of NCX1 were exposed to μ-calpain and their Na(+)-dependent (I(1)) and Ca(2+)-dependent (I(2)) regulatory phenotypes were assessed. For these exchangers, I(1) inactivation is evident as a Na(+)(i)-dependent decay of peak outward currents whereas I(2) regulation manifests as outward current activation by micromolar Ca(2+)(i) concentrations. Notably, with NCX1.1 and NCX1.4 but not in NCX1.3, higher Ca(2+)(i) levels alleviate I(1) inactivation. Our results show that (i) μ-calpain selectively ablates Ca(2+)-dependent (I(2)) regulation leading to a constitutive activation of exchange current, (ii) μ-calpain has much smaller effects on Na(+)-dependent (I(1)) regulation, produced by a slight destabilization of the I(1) state, and (iii) Ca(2+)-dependent regulation (I(2)) and Ca(2+)-mediated alleviation of I(1) appear to be functionally distinct mechanisms, the latter of which is left largely intact after μ-calpain treatment. The ability of μ-calpain to selectively and constitutively activate Na(+)-Ca(2+) exchange currents may have important pathophysiological implications in tissue where these splice variants are expressed.
Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre, University of Manitoba, Faculty of Medicine, 351 Tache Avenue, Winnipeg, Manitoba, Canada.
Mark
M
Hnatowich
Hoa Dinh
HD
Le
Danielle
D
DeMoissac
Kristy
K
Ranson
Vladimir
V
Yurkov
James S C
JS
Gilchrist
Alexander
A
Omelchenko
Larry V
LV
Hryshko
D017398:Alternative Splicing / Q000502:physiology*; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D004285:Dogs; D007668:Kidney / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009928:Organ Specificity / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D002154:Calpain