Multiple fatty acid sensing mechanisms operate in enteroendocrine cells: novel evidence for direct mobilization of stored calcium by cytosolic fatty acid.
Fatty acids (FA) with at least 12 carbon atoms increase intracellular Ca(2+) ([Ca(2+)](i)) to stimulate cholecystokinin release from enteroendocrine cells. Using the murine enteroendocrine cell line STC-1, we investigated whether candidate intracellular pathways transduce the FA signal, or whether FA themselves act within the cell to release Ca(2+) directly from the intracellular store. STC-1 cells loaded with fura-2 were briefly (3 min) exposed to saturated FA above and below the threshold length (C(8), C(10), and C(12)). C(12), but not C(8) or C(10), induced a dose-dependent increase in [Ca(2+)](i), in the presence or absence of extracellular Ca(2+). Various signaling inhibitors, including d-myo-inositol 1,4,5-triphosphate receptor antagonists, all failed to block FA-induced Ca(2+) responses. To identify direct effects of cytosolic FA on the intracellular Ca(2+) store, [Ca(2+)](i) was measured in STC-1 cells loaded with the lower affinity Ca(2+) dye magfura-2, permeabilized by streptolysin O. In permeabilized cells, again C(12) but not C(8) or C(10), induced release of stored Ca(2+). Although C(12) released Ca(2+) in other permeabilized cell lines, only intact STC-1 cells responded to C(12) in the presence of extracellular Ca(2+). In addition, 30 min exposure to C(12) induced a sustained elevation of [Ca(2+)](i) in the presence of extracellular Ca(2+), but only a transient response in the absence of extracellular Ca(2+). These results suggest that at least two FA sensing mechanisms operate in enteroendocrine cells: intracellularly, FA (>/=C(12)) transiently induce Ca(2+) release from intracellular Ca(2+) stores. However, they also induce sustained Ca(2+) entry from the extracellular medium to maintain an elevated [Ca(2+)](i).
Hira
Tohru
T
School of Biological Sciences, G.38 Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, United Kingdom.
Elliott
Austin C
AC
Thompson
David G
DG
Case
R Maynard
RM
McLaughlin
John T
JT
D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002244:Carbon / Q000737:chemistry; D002460:Cell Line; D002766:Cholecystokinin / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D019858:Enteroendocrine Cells / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005227:Fatty Acids / Q000378:metabolism*; D051379:Mice; D015398:Signal Transduction; D019284:Thapsigargin / Q000378:metabolism / Q000494:pharmacology; D013997:Time Factors; D010738:Type C Phospholipases / Q000378:metabolism
D004791:Enzyme Inhibitors; D005227:Fatty Acids; D019284:Thapsigargin; D002244:Carbon; D002766:Cholecystokinin; D010738:Type C Phospholipases; D001839:Bombesin; D002118:Calcium