Caffeine stores and dopamine differentially require Ca(2+) channels in goldfish somatotropes

Area of Science:

• Endocrinology
• Neuroendocrinology
• Cellular Signaling

Background:

• Intracellular calcium (Ca2+) stores play a critical role in regulating hormone secretion.
• Previous studies indicated that gonadotropin-releasing hormone (GnRH) stimulates GH release via intracellular Ca2+ stores.
• The specific mechanisms and temporal dynamics of these stores in neuroendocrine regulation require further elucidation.

Purpose of the Study:

• To investigate the role of intracellular Ca2+ stores in regulating growth hormone (GH) secretion in goldfish somatotropes.
• To characterize the caffeine-activated intracellular Ca2+ store and its modulation by ryanodine receptors.
• To compare the temporal requirements of Ca2+ channels in dopamine- and caffeine-evoked GH release.

Main Methods:

• Dissociation of goldfish pituitary cells to isolate somatotropes.
• Stimulation with caffeine and dopamine to evoke GH release.
• Application of ryanodine and blockade of Cd2+-sensitive Ca2+ channels to assess the involvement of specific pathways.

Main Results:

• Caffeine-stimulated GH release was partially mediated by caffeine-activated ryanodine receptors, with a ~28% reduction by ryanodine.
• The initial phase of dopamine-evoked GH release depended on Ca2+ channel activity.
• The initial phase of caffeine-evoked GH release was sensitive to prior blockade, suggesting Ca2+ influx is required for store maintenance.

Conclusions:

• Intracellular Ca2+ stores, particularly caffeine-activated ones involving ryanodine receptors, are crucial for GH secretion.
• Differential temporal requirements for Ca2+ channels in caffeine- and dopamine-evoked signaling suggest distinct regulatory mechanisms.
• This segregation of signaling pathways may allow for precise control of neuroendocrine regulation in teleosts.