Vanadium-containing tunicate blood cells are not highly acidic

Area of Science:

• Marine biology
• Cellular physiology
• Biochemistry

Background:

• Intracellular pH (pHi) is a critical regulator of cellular functions.
• Tunicates, like Ascidia nigra, possess unique vanadium-rich blood cells (vanadocytes) with poorly understood physiology.
• Accurate pHi measurement is essential for understanding cellular homeostasis in these organisms.

Purpose of the Study:

• To accurately determine the intracellular pH of intact Ascidia nigra blood cells.
• To investigate the pHi of specific cell types, particularly vanadocytes.
• To evaluate the suitability of existing pHi measurement techniques for vanadium-rich cells.

Main Methods:

• Intracellular pH measurement using the transmembrane equilibration of [14C] methylamine.
• Fractionation of Ascidia nigra blood cells to isolate vanadocytes.
• Comparison of the [14C] methylamine method with traditional techniques like cell lysis and vital staining.

Main Results:

• The intracellular pH of unfractionated Ascidia nigra blood cells was determined to be 7.39 ± 1.10.
• The intracellular pH of isolated vanadocytes was measured at 7.2.
• Traditional methods relying on cell lysis or vital staining were found to be unsuitable for these vanadium-rich cells, yielding inaccurate low pH values (<3.0).

Conclusions:

• The [14C] methylamine method provides a reliable means to measure intracellular pH in Ascidia nigra blood cells.
• Vanadocytes maintain a near-neutral intracellular pH of 7.2.
• The chemical properties of vanadium-containing cells necessitate specialized techniques for accurate intracellular pH determination, invalidating previously used methods.