Calcium equally increases the internal calcium recirculation fraction before and after beta-blockade in canine left ventricles.
We studied whether intracoronary Ca administration after beta-blockade would increase the internal Ca recirculation fraction (RF) analogously to the Ca administration before beta-blockade. This was performed in excised cross-circulated canine hearts. We analyzed the exponential decay component of the postextrasystolic potentiation (PESP) following a spontaneous extrasystole. All the PESPs decayed in alternans with atrial pacing at a constant rate. We obtained the time constant (tau(e)) of the monoexponential decay component of the alternans PESP. An increment of intracoronary Ca by 1.5 mmol/l enhanced the left ventricular contractility index Emax (end-systolic maximum elastance) by 2.5 times before and after beta-blockade with propranolol. The intracoronary Ca after beta-blockade slightly but significantly increased tau(e), and hence increased RF calculated from tau(e) by RF = exp(-1/tau(e)). This was analogous to the slightly increased tau(e) and RF with Ca before beta-blockade. We speculate that the myocardial cyclic AMP-dependent phosphorylation level would not significantly alter the effect of intracoronarily administered Ca on myocardial Ca handling, in terms of tau(e) and RF.
Hosogi
S
S
Department of Physiology II, Okayama University Medical School, Japan.
Araki
J
J
Syuu
Y
Y
Suzuki
S
S
Mohri
S
S
Mikane
T
T
Matsubara
H
H
Ohe
T
T
Hirakawa
M
M
Suga
H
H
D000249:Adenosine Monophosphate / Q000378:metabolism; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D002118:Calcium / Q000008:administration & dosage / Q000493:pharmacokinetics*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D003331:Coronary Vessels; D004195:Disease Models, Animal; D004285:Dogs; D004562:Electrocardiography / Q000187:drug effects; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D007269:Injections, Intra-Arterial; D009200:Myocardial Contraction / Q000187:drug effects; D011433:Propranolol / Q000494:pharmacology*
D000319:Adrenergic beta-Antagonists; D015220:Calcium Channels; D000249:Adenosine Monophosphate; D011433:Propranolol; D002118:Calcium