CALCIUM-INDEPENDENT SECRETION BY ATP-GAMMA-S FROM A PERMEABILIZED RATBASOPHILIC LEUKEMIA-CELL LINE (RBL-2H3)

Activation of rat basophilic leukaemia cells (RBL-2H3) leads to the se cretion of allergic and inflammatory mediators. These cells can be per meabilized, yet still retain their ability to secrete in response to a ntigen. Secretion can also be induced in permeabilized cells by the ad dition of the ATP analogue, ATP gamma S [adenosine-5'-O-(3-thiotriphos phate)], which is relatively resistant to phosphatase activity. ATP ga mma S-induced secretion (35-50% of total amine) is temperature and con centration-dependent. Calcium enhances secretion, but unlike antigen-i nduced secretion, it does occur in the absence of calcium and without the requirement for inositol phospholipid hydrolysis. Other ATP analog ues induced secretion in the rank order AMP-PNP greater than or equal to ATP gamma S >>> AMP-PCP > ATP alpha S = ATP [AMP-PNP, adenylyl-imid odiphosphate; AMP-PCP, adenylyl (beta,gamma-methylene)-diphosphonate; ATP alpha S, adenosine-5'-O-(1-thiotriphosphate)]. At equimolar concen trations, ATP inhibits ATP gamma S-induced secretion by 50%, but prolo nged incubation in the presence of ATP gamma S surmounts the ATP inhib ition. ADP is nearly as effective an inhibitor, but GTP and ITP are in effective. It is likely that secretion occurs through attachment at an ATP-binding site, effectively blocking the action of a phosphatase, a ctive later in the normal secretory pathway.