Effects of Strophanthidin on the Force-Frequency Relationship in Dog Ventricular Working and Conducting Tissues

犬心室乳頭肌或心肌柱與浦金氏纖維束分離後置組織皿中，以37℃ Tyrode氏液流灌，並以寬度2ms之閾上強度方波電刺激。動作電位、收縮張力與張力改變速率，均同時以示波器及多功能記錄器顯示、記錄或照相。實驗發現，心室肌之收縮力，於毒毛旋花配質(0.3~1×10^(-6)M)處理時增強，亦隨生理範圍內（60-120／分鐘）之刺激頻率加速而增強（正階梯）。浦金氏纖維則有下列不同反應：1．在相同刺激頻率範圍內，收縮力隨刺激頻率加速而降低（負階梯），2．相同濃度毒毛旋花配質引起之收縮力增強到達一高峰後即逐漸下降，收縮力增強作用未下降前，刺激頻率與收縮力之關係仍為負階梯，收縮力開始下降後則變為正階梯。3．收縮力隨細胞外鈣離子濃度增高而增強，鈣離子濃度過高(8.1-12.lmM)則收縮力增強之作用降低，收縮力增強作用未降低前，刺激頻率與收縮力之關係仍為負階梯，收縮力開始降低後則轉變為正階梯。此種鈣離子過高引起之變化，經鈣離子對抗劑處理後消失。實驗結果顯示心室肌與浦金氏纖維細胞內鈣離子濃度之調節機轉，基本性質相同，但在量方面則有差異。

關鍵字

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並列摘要

Effects of strophanthidin on force-frequency relationship were studied in dog working ventricular myocardium (VM) and Purkinje fibers (PF). In VM, both strophanthidin (0.3-1×10^(-6) M) and driving rate increase within physiological range of 1 to 2 Hz potentiated the force of contraction. In PF, the following different responses were observed. 1. The contractile force decreased as the driving rate increased within the same range (negative staircase). 2. The positive inotropic effect of strophanthidin first increased and then declined. During the rising phase of strophanthidin inotropy, the staircase was still negative. The staircase became positive as strophanthidin inotropy declined. 3. Strophanthidin also potentiated the contractile force of extrasystolic and post-extrasystolic beats as revealed by the Johnson's two-state experiments. 4. The inotropic effects of strophanthidin were mimicked by high [Ca(superscript 2+)](8.1-l2.1 mM) and reversed by Ca channel blockers. Effects of Ca(superscript 2+) overloading are discussed and a quantitative difference in regulation of cytosolic Ca(superscript 2+) between VM and PF is suggested.

並列關鍵字

strophanthidin inotropy ； force-frequency relationship ； Ca overloading ； ventricular tissues

國際替代計量

Effects of Strophanthidin on the Force-Frequency Relationship in Dog Ventricular Working and Conducting Tissues

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