Parkman H P, Pagano A P, Ringold M A, Ryan J P
Department of Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Regul Pept. 1996 May 7;63(1):31-7. doi: 10.1016/0167-0115(96)00023-7.
The aim of this study was to investigate the role of extracellular Ca2+ utilization in cholecystokinin (CCK) and acetylcholine-induced guinea pig gallbladder contractions by using agents that modulate influx of extracellular Ca2+ through voltage-dependent calcium channels.
Guinea pig gallbladder muscle strips were studied isometrically at Lmax in vitro.
(1) Acetylcholine and CCK caused dose-dependent contractions, with EDmax of 10(-4) and 10(-6) M, respectively. (2) Preventing influx of extracellular Ca2+ by incubation in Ca(2+)-free/0.1 mM EGTA solution inhibited the acetylcholine (10(-4) M)-induced contraction by 60 +/- 3% compared to only 46 +/- 5% (P < 0.05) for CCK (10(-6) M)-induced contraction. (3) Nifedipine (3 microM) inhibited the response to acetylcholine (10(-4) M) by 54 +/- 3%, compared to only 34 +/- 3% (P < 0.01) for CCK (10(-6) M). (4) Bay K 8644 (10(-7) M) significantly increased (P < 0.05) the contractile responses to low doses of each agonist: acetylcholine (10(-6) M) by 121 +/- 44% and CCK (10(-9) M) by 94 +/- 31%, but had no effect on the contraction to the EDmax of each agonist.
These studies demonstrate: (1) acetylcholine and CCK cause guinea pig gallbladder contraction by both intracellular Ca2+ release and influx of extracellular Ca2+ through voltage-dependent calcium channels; (2) the CCK-induced contraction is more dependent on intracellular Ca2+ than is acetylcholine; and (3) acetylcholine and CCK-induced contractions can by modulated by manipulating influx of extracellular Ca2+ through voltage-dependent calcium channels.
本研究的目的是通过使用调节细胞外Ca2+通过电压依赖性钙通道内流的药物，研究细胞外Ca2+利用在胆囊收缩素（CCK）和乙酰胆碱诱导的豚鼠胆囊收缩中的作用。
在体外等长条件下，于最大张力（Lmax）对豚鼠胆囊肌条进行研究。
（1）乙酰胆碱和CCK引起剂量依赖性收缩，最大效应剂量（EDmax）分别为10(-4) M和10(-6) M。（2）在无钙/0.1 mM乙二醇双四乙酸（EGTA）溶液中孵育以阻止细胞外Ca2+内流，与CCK（10(-6) M）诱导的收缩仅被抑制46±5%相比，乙酰胆碱（10(-4) M）诱导的收缩被抑制60±3%（P<0.05）。（3）硝苯地平（3 microM）抑制对乙酰胆碱（10(-4) M）的反应达54±3%，而对CCK（10(-6) M）的反应仅被抑制34±3%（P<0.01）。（4）Bay K 8644（10(-7) M）显著增加（P<0.05）对低剂量每种激动剂的收缩反应：对乙酰胆碱（10(-6) M）增加121±44%，对CCK（10(-9) M）增加94±31%，但对每种激动剂最大效应剂量的收缩无影响。
这些研究表明：（1）乙酰胆碱和CCK通过细胞内Ca2+释放和细胞外Ca2+通过电压依赖性钙通道内流引起豚鼠胆囊收缩；（2）CCK诱导的收缩比乙酰胆碱更依赖于细胞内Ca2+；（3）乙酰胆碱和CCK诱导的收缩可通过操纵细胞外Ca2+通过电压依赖性钙通道的内流来调节。
