Calcium dynamics during physiological acidification in Xenopus oocyte.

Area of Science:

• Cellular Physiology
• Ion Homeostasis
• Oocyte Biology

Background:

• The interplay between intracellular pH (pHi) and calcium ([Ca2+]i) is not fully understood.
• Changes in proton and calcium homeostasis are observed during physiological events like Xenopus laevis oocyte maturation.

Purpose of the Study:

• To investigate the relationship between pHi and [Ca2+]i in Xenopus oocytes.
• To elucidate the mechanisms of calcium mobilization induced by intracellular acidification.

Main Methods:

• Utilized NH4Cl and extracellular pH (pHe) changes to induce physiological intracellular acidification.
• Employed voltage-clamping, calcium imaging, and the triple-step protocol to analyze ion currents and calcium dynamics.
• Used BAPTA-AM, caffeine, heparin, MOPS, and lanthanum to investigate calcium sources and buffer pHi.

Main Results:

• NH4Cl-induced acidification triggered an inward current, primarily a Ca2+-dependent chloride current (ICl-Ca).
• Intracellular acidification led to a significant increase in [Ca2+]i, involving both calcium release and influx.
• The calcium pathways activated by pHe changes mirrored those activated by NH4Cl.

Conclusions:

• Intracellular acidification, whether induced by NH4Cl or pHe changes, stimulates [Ca2+]i increase through both calcium release and influx.
• Xenopus oocytes possess a robust signaling mechanism to manage environmental pH variations by modulating calcium homeostasis.