Function-specific calcium stores selectively regulate growth hormone secretion, storage, and mRNA level.
Ca(+) stores may regulate multiple components of the secretory pathway. We examined the roles of biochemically independent intracellular Ca(2+) stores on acute and long-term growth hormone (GH) release, storage, and mRNA levels in goldfish somatotropes. Thapsigargin-evoked intracellular Ca(2+) concentration ([Ca(2+)](i)) signal amplitude was similar to the Ca(2+)-mobilizing agonist gonadotropin-releasing hormone, but thapsigargin (2 microM) did not acutely increase GH release, suggesting uncoupling between [Ca(2+)](i) and exocytosis. However, 2 microM thapsigargin affected long-term secretory function. Thapsigargin-treated cells displayed a steady secretion of GH (2, 12, and 24 h), which decreased GH content (12 and 24 h), but not GH mRNA/production (24 h). In contrast to the results with thapsigargin, activating the ryanodine (Ry) receptor (RyR) with 1 nM Ry transiently increased GH release (2 h). Prolonged activation of RyR (24 h) reduced GH release, contents and apparent production, without changing GH mRNA levels. Inhibiting RyR with 10 microM Ry increased GH mRNA levels, production, and storage (2 h). Increasing [Ca(2+)](i) independently of Ca(2+) stores with the use of 30 mM KCl decreased GH mRNA. Collectively, these results suggest that parts of the secretory pathway can be controlled independently by function-specific Ca(2+) stores.
Johnson
James D
JD
Department of Biological Sciences, University of Alberta, Edmonton, T6G 2E9, Canada T2N 1N4.
Klausen
Christian
C
Habibi
Hamid R
HR
Chang
John P
JP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D005089:Exocytosis; D006054:Goldfish; D013006:Growth Hormone / Q000235:genetics* / Q000378:metabolism*; D010902:Pituitary Gland / Q000737:chemistry / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis*; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction; D019284:Thapsigargin / Q000494:pharmacology
D012333:RNA, Messenger; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D011189:Potassium Chloride; D019284:Thapsigargin; D013006:Growth Hormone; D003513:Cycloheximide; D002118:Calcium