Siegl P K, McNeill J H
Can J Physiol Pharmacol. 1982 Jan;60(1):33-40. doi: 10.1139/y82-004.
Inotropic responses to cumulative additions of methoxamine (10(-7) to 3 X 10(-4) M), isoproterenol (10(-9) to 10(-5) M), or calcium (2 to 32 mM) were measured in isolated rat left atria and papillary muscles and rabbit right ventricular papillary muscles at three stimulation frequencies. Cardiac muscles were incubated in oxygenated Chenoweth-Koelle solution (2 mM calcium) at 37 degrees C. The basal developed force (BDF) before and maximum developed force (MDF) after challenge with methoxamine and isoproterenol were inversely related to stimulation frequency in rat preparations. BDF was directly related to stimulation rate in rabbit papillary muscles while MDF was independent of the rate. Drug-induced increases in force (MDF - BDF) were independent of stimulation frequency in rat and inversely related to stimulation frequency in rabbit. Responses to calcium were similar to the observed adrenergic responses. Also, force-frequency relationships of the rat and rabbit preparations were not similar in the absence and presence of these agonists. These data show that inotropic responses by rat and rabbit hearts are not affected similarly by stimulation frequency and this may reflect a species difference in the utilization of extracellular calcium for contraction.
在三种刺激频率下，测定了离体大鼠左心房和乳头肌以及兔右心室乳头肌对甲氧明（10⁻⁷至3×10⁻⁴M）、异丙肾上腺素（10⁻⁹至10⁻⁵M）或钙（2至32mM）累积添加的变力反应。心肌在37℃的含氧Chenoweth-Koelle溶液（2mM钙）中孵育。在大鼠标本中，用甲氧明和异丙肾上腺素刺激前的基础发育力（BDF）和刺激后的最大发育力（MDF）与刺激频率呈负相关。在兔乳头肌中，BDF与刺激频率直接相关，而MDF与刺激频率无关。药物诱导的力增加（MDF - BDF）在大鼠中与刺激频率无关，而在兔中与刺激频率呈负相关。对钙的反应与观察到的肾上腺素能反应相似。此外，在不存在和存在这些激动剂的情况下，大鼠和兔标本的力-频率关系也不相似。这些数据表明，大鼠和兔心脏的变力反应受刺激频率的影响不同，这可能反映了在利用细胞外钙进行收缩方面的种属差异。
