The F-actin cytoskeleton modulates slow secretory components rather than readily releasable vesicle pools in bovine chromaffin cells

Adrenal chromaffin cells were used to test the role of the peripheral cytos keleton of F-actin in controlling different vesicle pools. Phorbol 12-myris tate 13-acetate and calyculin A, two substances affecting phosphorylation-d ephosphorylation cycles, produced different degrees of F-actin reorganizati on, inducing the partial and the almost total disassembly of this structure , respectively, as visualized using rhodamine-phalloidin staining. Conseque ntly, electron microscopy studies revealed the higher efficiency of calycul in-A over phorbol 12-myristate 13-acetate in promoting vesicle access to th e plasmalemma boundary. Surprisingly, only the phorbol ester enhanced fast kinetics and the population of rapidly releasable vesicle pools as studied by single-cell amperometry, whereas both agents, as well as the F-actin sev ering compound, Latrunculin A, promoted an increase in the population of ve sicles recruited in response to prolonged or repetitive stimulations. Taken together, our data support the notion that the F-actin peripheral bar rier controls primary granule recruitment from reserve vesicle pools, where as the phorbol ester effect on the rapidly releasable pools might be relate d to the alteration of late secretory stage through protein kinase C-depend ent phosphorylation of an unidentified target. (C) 2000 IBRO. Published by Elsevier Science Ltd. All rights reserved.