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Plant cells maintain a low luminal pH in the Trans-Golgi-Network/Early Endosome (TGN/EE), the organelle in which the secretory and endocytic pathways intersect. Impaired TGN/EE pH regulation translates into severe plant growth defects. The identity of the proton pump and proton/ion antiporters that regulate TGN/EE pH have been determined, but an essential component required to complete the TGN/EE membrane transport circuit remains unidentified - a pathway for cation and anion efflux. Here, we have used complementation, genetically encoded fluorescent sensors, and pharmacological treatments to demonstrate that Arabidopsis Cation Chloride Cotransporter (CCC1) is this missing component necessary for regulating TGN/EE pH and function. Loss of CCC1 function leads to alterations in TGN/EE-mediated processes including endocytic trafficking, exocytosis and response to abiotic stress, consistent with the multitude of phenotypic defects observed in ccc1 knockout plants. This discovery places CCC1 as a central component of plant cellular function.

We examined the effect of L364718, a new cholecystokinin (CCK) receptor antagonist, on amylase release stimulated by CCK or different secretagogues in isolated rat pancreatic acini. L364718 caused a parallel rightward shift of the dose-response curve of CCK8. Schild plots showed a slope of 1.05 t 0.15 and a pA2 value of 10.01 * 0.31. L364718 inhibited maximally stimulated amylase release by CCK in a dose-dependent manner, with half maximal inhibition (ID5,) at 1.7 nM and complete inhibition at 30 nM. Asperlicin, a prototype compound of L3M718, also caused dose-dependent inhibition, but L364718 was approximately 400 times morc potent than asperlicin (IDSo = 761 nM). L364718 significantly inhibited amylase release in response to CCK33 and CCK8 but had no effect on amylase release stimulated by other receptor secretagogues or agents bypassing receptors. The results indicate that L364718 acts as an extremcly potent, competitive, and specific antagonist of CCK's action on pancreatic acini. Key Words: L3647 18-Asperlicin-Amylase release-Pancreatic acinar cells.L364718 has been recently shown to be a potent nonpeptide cholecystokinin (CCK) receptor antagonist. The compound is synthesized starting from the asperlicin structure, which was formerly isolated from the fungus Aspergillus alliaceirs (1).Using '*'I-labeled CCK8 and 3H-labeled L3647 18, Chang et al. (2,3) have demonstrated that L364718 has an extremely high affinity for pancreatic and gallbladder CCK receptor and is highly selective for peripheral CCK receptors when compared with gastrin and brain CCK receptors. L364718 is also shown to act as an antagonist of CCK on gallbladder contraction (2,4), gastric emptying (4,5), and pancreatic secretion (4). We (6) have demonstrated that L364718 caused a potent inhibition of