Activation of the store-operated calcium current ICRAC can be dissociated from regulated exocytosis in rat basophilic leukaemia (RBL-1) cells.
In many cell types, the emptying of intracellular Ca2+ stores results in the opening of store-operated Ca2+ channels in the plasma membrane. However, the nature of the signal that couples store content to the opening of these Ca2+ channels is unclear. One model proposes that the Ca2+ channels are initially stored in cytoplasmic vesicles but inserted into the plasma membrane upon store depletion via a regulated exocytoytic mechanism (vesicular fusion model). Using the whole-cell patch-clamp technique to measure the store-operated Ca2+ current ICRAC and the capacitance method to monitor vesicular fusion, an indicator of exocytosis, we have investigated the effects of interfering with regulated exocytosis on the ability of ICRAC to activate. We find that the recombinant protein alpha-SNAP1-285, an inhibitor of exocytosis in many systems, suppresses such fusion but has no impact on the activation of ICRAC. A variety of other manoeuvres that interfere with vesicle trafficking and exocytosis were also without effect on ICRAC. Impairing constitutive exocytosis with brefeldin A reduced the extent of ICRAC, but this effect was less pronounced when current density was considered instead. Activation of ICRAC can therefore be clearly dissociated from an exocytotic mechanism, a finding that is not easily reconcilable with the vesicular fusion model.
Laboratory of Molecular and Cellular Signalling, Department of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK.
Daniel
D
Bakowski
Robert D
RD
Burgoyne
Anant B
AB
Parekh
D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics / Q000494:pharmacology; D045744:Cell Line, Tumor; D025802:Electric Capacitance; D005033:Ethylmaleimide / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D015471:Leukemia, Basophilic, Acute / Q000473:pathology / Q000503:physiopathology; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000235:genetics / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000494:pharmacology; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013744:Tetanus Toxin / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D033921:Vesicular Transport Proteins; D018631:ras Proteins / Q000378:metabolism
D015220:Calcium Channels; D002352:Carrier Proteins; D008565:Membrane Proteins; D009842:Oligopeptides; D011994:Recombinant Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013744:Tetanus Toxin; D033921:Vesicular Transport Proteins; C088459:B 581; D020126:Brefeldin A; D019284:Thapsigargin; D018631:ras Proteins; D005033:Ethylmaleimide; D002118:Calcium