Initiation of purinergic signaling by exocytosis of ATP-containing vesicles in liver epithelium.
Extracellular ATP represents an important autocrine/paracrine signaling molecule within the liver. The mechanisms responsible for ATP release are unknown, and alternative pathways have been proposed, including either conductive ATP movement through channels or exocytosis of ATP-enriched vesicles, although direct evidence from liver cells has been lacking. Utilizing dynamic imaging modalities (confocal and total internal reflection fluorescence microscopy and luminescence detection utilizing a high sensitivity CCD camera) at different scales, including confluent cell populations, single cells, and the intracellular submembrane space, we have demonstrated in a model liver cell line that (i) ATP release is not uniform but reflects point source release by a defined subset of cells; (ii) ATP within cells is localized to discrete zones of high intensity that are approximately 1 mum in diameter, suggesting a vesicular localization; (iii) these vesicles originate from a bafilomycin A(1)-sensitive pool, are depleted by hypotonic exposure, and are not rapidly replenished from recycling of endocytic vesicles; and (iv) exocytosis of vesicles in response to cell volume changes depends upon a complex series of signaling events that requires intact microtubules as well as phosphoinositide 3-kinase and protein kinase C. Collectively, these findings are most consistent with an essential role for exocytosis in regulated release of ATP and initiation of purinergic signaling in liver cells.
Feranchak
Andrew P
AP
Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9030, USA. drew.feranchak@UTSouthwestern.edu
Lewis
Matthew A
MA
Kresge
Charles
C
Sathe
Meghana
M
Bugde
Abhijit
A
Luby-Phelps
Kate
K
Antich
Peter P
PP
Fitz
J Gregory
JG
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D019898:Autocrine Communication / Q000502:physiology; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D048429:Cell Size; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism*; D008113:Liver Neoplasms; D018942:Macrolides / Q000494:pharmacology; D018613:Microscopy, Confocal; D019899:Paracrine Communication / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011983:Receptors, Purinergic / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D022161:Transport Vesicles / Q000502:physiology*; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism
D004791:Enzyme Inhibitors; D018942:Macrolides; D011983:Receptors, Purinergic; C040929:bafilomycin A1; D000255:Adenosine Triphosphate; D011493:Protein Kinase C; D025262:Vacuolar Proton-Translocating ATPases