Bridge J H, Spitzer K W, Ershler P R
Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, UT.
Science. 1988 Aug 12;241(4867):823-5. doi: 10.1126/science.3406740.
Cell contraction and relaxation were measured in single voltage-clamped guinea pig cardiomyocytes to investigate the contribution of sarcolemmal Na+-Ca2+ exchange to mechanical relaxation. Cells clamped from -80 to 0 millivolts displayed initial phasic and subsequent tonic contractions; caffeine reduced or abolished the phasic and enlarged the tonic contraction. The rate of relaxation from tonic contractions was steeply voltage-dependent and was significantly slowed in the absence of a sarcolemmal Na+ gradient. Tonic contractions elicited in the absence of a Na+ gradient promptly relaxed when external Na+ was applied, reflecting activation of Na+-Ca2+ exchange. It appears that a voltage-dependent Na+-Ca2+ exchange can rapidly mechanically relax mammalian heart muscle.
在单个电压钳制的豚鼠心肌细胞中测量细胞收缩和舒张，以研究肌膜钠钙交换对机械舒张的作用。钳制在-80至0毫伏的细胞表现出初始的阶段性收缩和随后的强直性收缩；咖啡因减少或消除了阶段性收缩并增大了强直性收缩。强直性收缩的舒张速率高度依赖电压，并且在没有肌膜钠梯度的情况下显著减慢。在没有钠梯度的情况下引发的强直性收缩，当施加细胞外钠时会迅速舒张，这反映了钠钙交换的激活。看来电压依赖性钠钙交换可以迅速使哺乳动物心肌产生机械舒张。
