Evidence that IP3 and ryanodine-sensitive intra-cellular Ca2+ stores are not involved in acute hyposmotically-induced prolactin release in Tilapia.
Prolactin (PRL) cells from the euryhaline tilapia, Oreochromis mossambicus, behave like osmoreceptors by responding directly to reductions in medium osmolality with increased secretion of the osmoregulatory hormone PRL. Extracellular Ca(2+) is essential for the transduction of a hyposmotic stimulus into PRL release. In the current study, the presence and possible role of intracellular Ca(2+) stores during hyposmotic stimulation was investigated using pharmacological approaches. Changes in intracellular Ca(2+) concentration were measured with fura-2 in isolated PRL cells. Intracellular Ca(2+) stores were depleted in dispersed PRL cells with thapsigargin (1 microM) or cyclopiazonic acid (CPA, 10 microM). Pre-incubation with thapsigargin prevented the rise in [Ca(2+)](i) induced by lysophosphatidic acid (LPA, 1 microM), an activator of the IP(3) signalling cascade, but did not prevent the hyposmotically-induced rise in [Ca(2+)](i) in medium with normal [Ca(2+)] (2mM). Pre-treatment with CPA produced similar results. Prolactin release from dispersed cells followed a pattern that paralleled observed changes in [Ca(2+)](i). CPA inhibited LPA-induced prolactin release but not hyposmotically-induced release. Xestospongin C (1microM), an inhibitor of IP(3) receptors, had no effect on hyposmotically-induced PRL release. Pre-exposure to caffeine (10mM) or ryanodine (1microM) did not prevent a hyposmotically-induced rise in [Ca(2+)](i). Taken together these results indicate the presence of IP(3) and ryanodine-sensitive Ca(2+) stores in tilapia PRL cells. However, the rapid rise in intracellular [Ca(2+)] needed for acute PRL release in response to hyposmotic medium can occur independently of these intracellular Ca(2+) stores.
Seale
André P
AP
Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe 96744, USA.
Cooke
Ian M
IM
Hirano
Tetsuya
T
Grau
Gordon E
GE
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism*; D008246:Lysophospholipids / Q000378:metabolism; D009995:Osmosis; D009997:Osmotic Pressure; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D017210:Tilapia / Q000378:metabolism*
D004791:Enzyme Inhibitors; D007295:Inositol Phosphates; D008246:Lysophospholipids; D012433:Ryanodine; C092449:inositol 1,2,3-trisphosphate; D011388:Prolactin; C032881:lysophosphatidic acid; D002118:Calcium