Effects of Cholecystokinin (CCK)-JMV-180 on the CCK Receptors of Rabbit Pancreatic Acini and Gallbladder Smooth Muscle

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Effects of cholecystokinin (CCK)-JMV-180, a CCK analog, on the CCK receptor functions of isolated rabbit pancreatic acini and gallbladder smooth muscle were studied. When the pancreatic acini were incubated with increasing concentrations of CCK-8, stimulation of amylase release reached a maximum at 3 nM and then declined with the increasing concentration of CCK-8. CCK-JMV-180 also caused a dosedependent amylase release stimulation, which plateaued and remained unchanged above 300 nM at about 50% of the maximal stimulation by CCK-8. CCK-JMV-180 above 100 nM caused a rightward shift of the downstroke of the dose-response curve for CCK-8 (pA₂=7.5). In the gallbladder smooth muscle, CCK-8 caused a dose-dependent contraction, but CCK-JMV-180 totally lacked this property. Instead, CCK-JMV-180 caused a rightward shift of the dose-response curve for CCK-8 (pA₂=7.9). These results suggest that CCK-JMV-180 distinguishes between the CCK_A receptors associated with pancreatic exocrine secretion in the acini and those involved in contraction of the isolated gallbladder smooth muscle in rabbits.