title: Calcium and GTP-gamma-S as single effectors of secretion from permeabilized rat mast cells: requirements for ATP.
abstract: Treatment with metabolic inhibitors and addition of exogenous MgATP exerted different effects on secretion from streptolysin-O-permeabilized mast cells, responding to calcium and GTP-gamma-S as single effectors (i.e., independently of each other). These effects were also strongly dependent on the experimental conditions. Thus cells, triggered by Ca2+ at the time of permeabilization, did not require MgATP, but after metabolic inhibition rapidly became absolutely dependent on its provision, requiring high (> mM) concentrations. AMP-PNP was not effective. After longer treatment with metabolic inhibitors, the absolute dependence on MgATP was also exhibited by cells responding to dual effectors (i.e., Ca2+ and GTP-gamma-S applied together). In contrast, calcium independent secretion due to GTP-gamma-S was more resistant to metabolic inhibition, exhibiting no absolute requirements for MgATP. Once the responsiveness to GTP-gamma-S had been lost, it could not be restored by addition of MgATP. MgATP, in fact, inhibited the response of permeabilized cells to GTP-gamma-S. This effect could be mimicked by AMP-PNP. When permeabilized cells were washed before triggering, MgATP (0.1-1 mM concentration range) was no longer inhibitory but stimulatory. These differences between Ca(2+)- and GTP-gamma-S-induced responses indicate that ATP utilization is essential to the calcium, but not to the guanine nucleotide, pathway to secretion. The rate of the response to calcium/MgATP was much slower in the absence than in the presence of GTP-gamma-S. The onset of secretion occurred after an initial delay. This lag phase was abolished by addition of GTP-gamma-S, suggesting that a GTP-binding protein may control a reaction which constitutes a rate-limiting step in the secretory process.
authors: Department of Physiology, University College London, UK.
authors: A
authors: A
authors: Koffer
authors: Y
authors: Y
authors: Churcher
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis / Q000494:pharmacology; D000818:Animals; D001426:Bacterial Proteins; D002118:Calcium / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D008297:Male; D008407:Mast Cells / Q000187:drug effects* / Q000378:metabolism; D010529:Peritoneal Cavity; D010539:Permeability; D010743:Phospholipids / Q000032:analysis; D010750:Phosphoproteins / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013301:Streptolysins; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D010743:Phospholipids; D010750:Phosphoproteins; D013301:Streptolysins; C025964:streptolysin O; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000255:Adenosine Triphosphate; D002118:Calcium