Cell to cell communication and pH in the frog lens

Area of Science:

• Ophthalmology
• Cell Biology
• Biophysics

Background:

• Lens fiber cells are interconnected by gap junctions, facilitating solute transport between peripheral and inner cells.
• Transmembrane transport is predominantly handled by peripheral cells.
• Gap junctions play a crucial role in maintaining lens homeostasis and function.

Purpose of the Study:

• To develop and apply a novel method for measuring cell-to-cell resistance in intact lens fiber cells at varying depths.
• To investigate the intracellular pH distribution within the intact lens.
• To characterize the differential pH sensitivity and coupling resistance of gap junctions in peripheral versus inner lens fiber cells.

Main Methods:

• Utilized a two-intracellular microelectrode technique to measure cell-to-cell resistance.
• Employed ion-sensitive microelectrodes for recording intracellular pH at different depths.
• Manipulated intracellular pH using CO2 bubbling to assess gap junction response.

Main Results:

• Identified a transition zone (500-650 microns) where gap junction properties change.
• Peripheral fiber cells exhibit a specific coupling resistance of 1.1 Ω cm², while inner cells have 2.7 Ω cm².
• Peripheral gap junctions uncouple (resistance increases >40-fold) upon acidification, whereas inner junctions remain largely unaffected.

Conclusions:

• Gap junctions in the lens exhibit depth-dependent variations in resistance and pH sensitivity.
• Peripheral lens cells maintain an alkaline intracellular pH (7.02) via Na/H exchange, while inner cells are more acidic (6.81).
• The reduced pH sensitivity of inner fiber cell gap junctions may be vital for lens survival in its acidic interior environment.