High osmolality: a potent XXXX hormone secretogogue in dispersed @entity3243 cells.

@entity268 @entity935 @entity1219 @entity3044 @entity969 @entity24585 @entity460 @entity141 @entity3243 @entity2827 @entity291
We have examined possible mechanisms by which osmolality might modulate @entity24585 secretion in dispersed @entity291 @entity3243 cells. Increasing medium osmolality by adding @entity2827 causes a marked, dose-dependent increase in @entity24585 release. The maximum effect (4-fold increase) is observed when osmolality is around 650 mosM, with half-maximal stimulation at about 400 mosM. When osmolality is increased to a similar extent with either sucrose or @entity2827 , @entity24585 secretion is enhanced to a comparable degree, suggesting that osmolality itself, rather than ionic strength, is responsible for the increase in @entity24585 secretion. Time course experiments show that the increased secretion of @entity24585 with high osmolality occurs very rapidly (in less than 5 min). In contrast to the suppressive effects of high @entity141 on @entity24585 release, increasing @entity460 concentration in the incubation media does not inhibit the stimulation of @entity24585 secretion by high osmolality. Moreover, the effects of @entity935 (10(-5) M) and high osmolality on @entity24585 release are additive, further suggesting that high osmolality and @entity268 modulate @entity24585 release by different mechanisms. In fact, direct measurement of cellular @entity268 in cells exposed to high osmolality shows no change relative to control cells incubated with normal osmolality, 127 +/- 20 vs. 146 +/- 21 fmol/10(5) cells, respectively. Cytosolic @entity141 increases from 257 +/- 29 nM to 703 +/- 50 nM after 200 mM @entity1219 is added to the incubation medium at low @entity141 (0.5mM). Prior removal of extracellular @entity460 abolished this effect. Increasing the osmolality to a similar level by adding @entity969 to the medium does not demonstrate any increase in cytosolic @entity460 . We conclude that high osmolality is a potent secretogogue in dispersed @entity291 @entity3243 cells. Unlike @entity935 and @entity3044 , high osmolality does not act through changes in intracellular @entity268 . It also prevents the normal inhibitory effect of high @entity141 on @entity24585 release. Change of cytosolic @entity141 is variable and suggests that the effect of high osmolality on @entity24585 release cannot be explained by cytosolic @entity141 alone. Further understanding of the mechanisms by which osmolality affects @entity24585 release, therefore, may provide clues to the unusual inverse relationship between extracellular and cytosolic @entity460 and @entity24585 release.
