pH homeostasis in human lymphocytes: modulation by ions and mitogen

Area of Science:

• Cellular Physiology
• Immunology
• Biochemistry

Background:

• Quiescent human peripheral blood lymphocytes exhibit a stable intracellular pH (7.0-7.2) across a physiological extracellular pH range (6.9-7.4).
• Intracellular pH regulation is crucial for cellular function and response to stimuli.

Purpose of the Study:

• To investigate the mechanisms of intracellular pH regulation in human lymphocytes.
• To determine the relationship between intracellular pH homeostasis and mitogen-induced lymphocyte proliferation.
• To examine the effects of ATP levels and extracellular ion concentrations (Na+, K+) on lymphocyte pH regulation.

Main Methods:

• Measurement of intracellular pH using 19F nuclear magnetic resonance spectroscopy.
• Assessment of intracellular pH via [14C]5,5-dimethyloxazolidine-2,4-dione (DMO) equilibrium distribution.
• Manipulation of intracellular ATP levels and extracellular Na+/K+ concentrations.

Main Results:

• Decreased ATP levels abolished active pH regulation, resulting in a constant pH gradient (0.2 pH units, acid inside).
• Low extracellular Na+ inhibited proliferation but did not affect pH regulation, while high K+ (low Na+) disrupted pH homeostasis but restored proliferation.
• Mitogen stimulation did not significantly alter intracellular pH in the initial hours of culture, and prolonged mitogen exposure led to loss of pH homeostasis.

Conclusions:

• Intracellular pH regulation in lymphocytes is an active, ATP-dependent process.
• Lymphocyte proliferation and pH regulation are differentially influenced by extracellular ion composition.
• A shift in intracellular pH is not a prerequisite for mitogen-induced lymphocyte proliferation.