Altered Ca(2+) handling by ryanodine receptor and Na(+)-Ca(2+) exchange in the heart from ovariectomized rats: role of protein kinase A.
Our previous study has demonstrated that ovariectomy (Ovx) significantly increased the left ventricular developed pressure (LVDP) and the maximal rate of developed pressure over time (+/-dP/dt(max)) in the isolated perfused rat heart and the effects were reversed by female sex hormone replacement. In the present investigation, we studied the effects of Ovx for 6 wk on Ca(2+) homeostasis that determines the contractile function. Particular emphasis was given to Ca(2+) handling by ryanodine receptor (RyR) and Na(+)-Ca(2+) exchange (NCX). (45)Ca(2+) fluxes via the RyR, NCX, and Ca(2+)-ATPase (SERCA) were compared with their expression in myocytes from Ovx rats with and without estrogen replacement. Furthermore, we correlated the handling of Ca(2+) by these Ca(2+) handling proteins with the overall Ca(2+) homeostasis by determining the Ca(2+) transients induced by electrical stimulation and caffeine, which reveals the dynamic changes of cytosolic Ca(2+) concentration ([Ca(2+)](i)) in the heart. In addition, we determined the expression and contribution of protein kinase A (PKA) to the regulation of the aforementioned Ca(2+) handling proteins in Ovx rats. It was found that after Ovx there were 1) increased Ca(2+) fluxes via RyR and NCX, which were reversed not only by estrogen replacement, but more importantly by blockade of PKA; 2) an increased expression of PKA; and 3) no increase in expression of NCX and SERCA. We suggest that hyperactivities of RyR and NCX are a result of upregulation of PKA. The increased release of Ca(2+) through RyR and removal of Ca(2+) by NCX are believed to be responsible for the greater contractility and faster relaxation after Ovx.
Kravtsov
Gennadi M
GM
Department of Physiology, 4/F Laboratory Block, Faculty of Medicine Bldgs., 21 Sassoon Rd., Pokfulam, Hong Kong SAR, China.
Kam
Kenneth W L
KW
Liu
Jing
J
Wu
Song
S
Wong
Tak Ming
TM
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004558:Electric Stimulation; D004967:Estrogens / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D006706:Homeostasis; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010052:Ovariectomy; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D013997:Time Factors; D015854:Up-Regulation; D016277:Ventricular Function, Left
D004967:Estrogens; D047428:Protein Kinase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D019831:Sodium-Calcium Exchanger; D002110:Caffeine; D017868:Cyclic AMP-Dependent Protein Kinases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases