Multiple calcium mobilization pathways in single avian salt gland cells

Area of Science:

• Cell Physiology
• Ion Transport
• Biochemistry

Background:

• Avian salt glands are crucial for osmoregulation.
• Intracellular calcium signaling plays a vital role in cellular functions, including secretion.

Purpose of the Study:

• To investigate the mechanisms of agonist-induced intracellular calcium changes in avian salt gland cells.
• To differentiate between calcium release from intracellular stores and calcium influx from extracellular sources.
• To explore the pathways involved in refilling intracellular calcium stores.

Main Methods:

• Dual-wavelength microspectrofluorimetry using fura-2 to measure intracellular calcium concentration ([Ca2+]i).
• Stimulation with cholinergic agonist carbachol.
• Manipulation of extracellular calcium levels and use of calcium entry blockers (Ni2+, La3+).

Main Results:

• Carbachol stimulation caused a rapid, sustained increase in [Ca2+]i.
• The initial increase was transient without extracellular Ca2+ or with Ni2+, indicating intracellular Ca2+ release.
• Sustained increase required extracellular Ca2+, indicating Ca2+ influx.
• Two distinct Ca2+ entry mechanisms were suggested: one agonist-induced and sensitive to blockers, another for refilling intracellular stores and insensitive to blockers.
• Spontaneous [Ca2+]i oscillations were observed in some cells, originating from the agonist-sensitive intracellular pool.

Conclusions:

• Avian salt gland cells utilize both intracellular calcium release and extracellular calcium influx for agonist-induced signaling.
• Distinct calcium entry pathways regulate cellular calcium homeostasis and store refilling.
• Intracellular calcium dynamics are complex, involving multiple regulatory mechanisms and exhibiting spontaneous oscillations in a subset of cells.