Hosogi S, Araki J, Syuu Y, Suzuki S, Mohri S, Mikane T, Matsubara H, Ohe T, Hirakawa M, Suga H
Department of Physiology II, Okayama University Medical School, Japan.
Heart Vessels. 1997;12(6):280-6. doi: 10.1007/BF02766804.
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.
我们研究了在β受体阻滞剂作用后冠状动脉内给予钙是否会像在β受体阻滞剂作用前给予钙一样增加心肌内钙再循环分数（RF）。这是在离体交叉循环犬心脏中进行的。我们分析了自发性期前收缩后期前收缩后增强（PESP）的指数衰减成分。在心房以恒定速率起搏时，所有的PESP均呈交替性衰减。我们获得了交替性PESP单指数衰减成分的时间常数（tau(e)）。在用普萘洛尔进行β受体阻滞剂作用前后，冠状动脉内钙增加1.5 mmol/l可使左心室收缩性指数Emax（收缩末期最大弹性）提高2.5倍。β受体阻滞剂作用后的冠状动脉内钙使tau(e)略有但显著增加，因此由tau(e)通过RF = exp(-1/tau(e))计算得出的RF增加。这与β受体阻滞剂作用前钙使tau(e)和RF略有增加的情况类似。我们推测，就tau(e)和RF而言，心肌环磷酸腺苷依赖性磷酸化水平不会显著改变冠状动脉内给予钙对心肌钙处理的影响。
