Patch clamp studies on TRPV4-dependent hemichannel activation in lens epithelium

Area of Science:

• Ophthalmology
• Cell Physiology
• Ion Channel Biology

Background:

• Adenosine triphosphate (ATP) release from the lens, mediated by hemichannels, is linked to Transient Receptor Potential Vanilloid 4 (TRPV4) activation during osmotic swelling.
• Understanding the precise relationship between TRPV4 activation and connexin hemichannel opening is crucial for lens physiology research.

Purpose of the Study:

• To investigate the functional link between TRPV4 activation and connexin hemichannel opening in cultured mouse lens epithelial cells.
• To determine if TRPV4 agonist GSK1016790A (GSK) induces hemichannel activity and if this is modulated by TRPV4 antagonist HC067047 (HC).

Main Methods:

• Patch-clamp recordings (whole-cell and cell-attached configurations) were performed on cultured mouse lens epithelial cells.
• Cells were treated with the TRPV4 agonist GSK1016790A (GSK) and the TRPV4 antagonist HC067047 (HC).
• Membrane current (Im) and single-channel conductance were measured under various voltage conditions.

Main Results:

• GSK administration caused a rapid, variable, and significant increase in non-selective whole-cell membrane conductance (Im) across a wide voltage range.
• The GSK-induced increase in Im was blocked by HC, confirming TRPV4 dependence.
• GSK treatment led to membrane depolarization and the disappearance of an outward K+ current, with its presence predicting GSK response.
• Single-cell recordings identified channel events with a conductance of 180-270 pS upon GSK application.

Conclusions:

• The findings strongly support the hypothesis of TRPV4-dependent opening of connexin 43 (Cx43) hemichannels in lens epithelial cells.
• This mechanism provides a direct link between TRPV4 activation, potentially due to osmotic stress, and hemichannel-mediated ATP release from the lens.