Iino S, Cui Y, Galione A, Terrar D A
Department of Pharmacology, University of Oxford, U.K.
Circ Res. 1997 Nov;81(5):879-84. doi: 10.1161/01.res.81.5.879.
Although it is becoming widely accepted that cADP-ribose (cADPR) can regulate calcium release from the endoplasmic reticulum in sea urchin eggs and in a variety of mammalian cell types, it remains controversial whether this substance might influence calcium release during excitation-contraction coupling in cardiac muscle. We have investigated possible actions of cADPR in intact cells isolated from guinea pig ventricle, paying particular attention to the possible influence of temperature. At 36 degrees C, myocyte contraction was influenced by cytosolic application of cADPR in a concentration-dependent manner (showing an approximately 30% increase in contraction with 5 mumol/L cADPR applied via a patch pipette in myocytes stimulated to fire action potentials at 1 Hz). Calcium transients measured with fura 2 were also increased by 5 mumol/L cADPR. Antagonists of cADPR reduced contraction at 36 degrees C (by approximately 35% with either 50 mumol/L 8-Br-cADPR or 5 mumol/L 8-amino-cADPR applied via the patch pipette). At room temperature (approximately 20 degrees C to 24 degrees C), no significant effects on contraction were detected with either cADPR or its antagonists. At 36 degrees C, treatment of the cells with a mixture of 2 mumol/L ryanodine and 1 mumol/L thapsigargin to suppress function of the sarcoplasmic reticulum stores of calcium prevented the action of 5 mumol/L cADPR applied via a patch pipette. These observations are consistent with an action of cytosolic cADPR to enhance calcium-induced calcium release from the sarcoplasmic reticulum in guinea pig ventricular myocytes at 36 degrees C. The observed influence of temperature under the conditions of our experiments is one factor that might help to account for failure to detect actions of cADPR and its analogues in some previous studies.
尽管环ADP核糖（cADPR）能够调节海胆卵及多种哺乳动物细胞类型中内质网的钙释放，这一观点正被广泛接受，但该物质是否会在心肌兴奋-收缩偶联过程中影响钙释放仍存在争议。我们研究了cADPR对从豚鼠心室分离出的完整细胞的可能作用，尤其关注温度的可能影响。在36℃时，心肌细胞收缩受到胞质中cADPR的浓度依赖性影响（在以1Hz刺激产生动作电位的心肌细胞中，通过膜片钳微量移液器施加5μmol/L cADPR时，收缩增加约30%）。用fura 2测量的钙瞬变也因5μmol/L cADPR而增加。cADPR拮抗剂在36℃时可降低收缩（通过膜片钳微量移液器施加50μmol/L 8-溴-cADPR或5μmol/L 8-氨基-cADPR时，收缩降低约35%）。在室温（约20℃至24℃）下，未检测到cADPR及其拮抗剂对收缩有显著影响。在36℃时，用2μmol/L兰尼碱和1μmol/L毒胡萝卜素的混合物处理细胞以抑制肌浆网钙储存功能，可阻止通过膜片钳微量移液器施加5μmol/L cADPR的作用。这些观察结果与胞质cADPR在36℃时增强豚鼠心室肌细胞中钙诱导的肌浆网钙释放的作用一致。在我们的实验条件下观察到的温度影响是一个因素，这可能有助于解释在一些先前研究中未能检测到cADPR及其类似物的作用。
