Gap junctional conductance is a simple and sensitive function of intracellular pH

Area of Science:

• Cell Biology
• Developmental Biology
• Biophysics

Background:

• Gap junctions mediate direct cell-to-cell communication in embryonic development.
• Cytoplasmic pH (pHi) is a critical regulator of cellular processes.
• The precise mechanisms by which pHi affects gap junction function are not fully understood.

Purpose of the Study:

• To investigate the quantitative relationship between cytoplasmic pH and gap junctional conductance in early embryos.
• To elucidate the kinetics and mechanism of pH-induced gap junction closure.

Main Methods:

• Measurement of cytoplasmic pH using pH-sensitive microelectrodes in amphibian (Ambystoma) and teleost (Fundulus) embryos.
• Assessment of junctional conductance in electrotonically coupled cell pairs.
• Analysis of the relationship between pHi and junctional conductance under varying pH conditions.

Main Results:

• Cytoplasmic pH in cleavage-stage blastomeres averages approximately 7.7.
• Acidification of the cytoplasm rapidly and reversibly reduces junctional conductance.
• The pH-gated closure follows a Hill curve (K = 50 nM, pK = 7.3, n = 4-5), indicating a cooperative mechanism involving multiple charged sites.

Conclusions:

• Gap junction channels are directly regulated by cytoplasmic pH.
• The observed cooperative binding of protons suggests direct interaction with channel macromolecules.
• The absence of hysteresis indicates protons act directly, not via cytoplasmic intermediates.