Ruth J A, Cuizon J V, Eiden L E
Neuropeptides. 1984 May;4(3):185-91. doi: 10.1016/0143-4179(84)90099-4.
Norepinephrine (NE) (10(-5) M) increases the beating rate of isolated, spontaneously beating guinea-pig atria 78 +/- 3 beats per minute. Leucine-enkephalin (10(-7) M) increases the maximal chronotropic response to NE by 38%, i.e., by 30 beats per minute. In the presence of 10(-7) M leucine-enkephalin and 10(-7) M naloxone, the chronotropic response to NE is reduced to 38 +/- 3 beats per minute, a value observed in the presence of naloxone alone. Neither naloxone nor leucine enkephalin significantly altered the inotropic response to NE, or significantly altered the basal beating rate. Parallel effects were observed when 45Ca++ uptake by atrial tissue was examined. Incubation of atrial slices with 10(-5) M NE for 10 minutes minimally stimulated 45Ca++ uptake from 1.27 +/- 0.04 to 1.45 +/- 0.17 nmol/mg tissue. In the presence of 10(-7) M leucine-enkephalin, 45Ca++ uptake was increased to 1.95 +/- 0.14 nmol/mg tissue. 45Ca++ uptake was reduced to control values (1.19 +/- 0.09 nmol/mg tissue) in the presence of NE, leucine-enkephalin and naloxone (10(-7) M). The data are consistent with a leucine-enkephalin augmentation of NE-induced chronotropy in guinea-pig atria due to an enhancement of NE-dependent Ca++ accumulation. This effect of leucine-enkephalin is opposite that previously reported for rat atria, in which leucine-enkephalin inhibits both NE-induced positive chronotropy and Ca++ influx.
去甲肾上腺素（NE）（10⁻⁵ M）可使离体的、自主搏动的豚鼠心房的搏动频率增加78±3次/分钟。亮氨酸脑啡肽（10⁻⁷ M）可使对NE的最大变时反应增加38%，即增加30次/分钟。在存在10⁻⁷ M亮氨酸脑啡肽和10⁻⁷ M纳洛酮的情况下，对NE的变时反应降至38±3次/分钟，这是仅存在纳洛酮时观察到的值。纳洛酮和亮氨酸脑啡肽均未显著改变对NE的变力反应，也未显著改变基础搏动频率。当检测心房组织对⁴⁵Ca²⁺的摄取时，观察到了类似的效应。将心房切片与10⁻⁵ M NE孵育10分钟，可使⁴⁵Ca²⁺摄取量从1.27±0.04 nmol/mg组织轻微刺激至1.45±0.17 nmol/mg组织。在存在10⁻⁷ M亮氨酸脑啡肽的情况下，⁴⁵Ca²⁺摄取量增加至1.95±0.14 nmol/mg组织。在存在NE、亮氨酸脑啡肽和纳洛酮（10⁻⁷ M）的情况下，⁴⁵Ca²⁺摄取量降至对照值（1.19±0.09 nmol/mg组织）。这些数据与亮氨酸脑啡肽通过增强NE依赖性Ca²⁺积累而增强豚鼠心房中NE诱导的变时性一致。亮氨酸脑啡肽的这种作用与先前报道的大鼠心房相反，在大鼠心房中，亮氨酸脑啡肽抑制NE诱导的确正性变时性和Ca²⁺内流。
