cGMP modulates transport across the ciliary epithelium

Area of Science:

• Ophthalmology
• Cell Physiology
• Molecular Biology

Background:

• Cyclic GMP (cGMP) is a crucial second messenger involved in various cellular processes.
• The ciliary epithelium plays a vital role in aqueous humor production and intraocular pressure regulation.
• Understanding the role of cGMP in ciliary epithelium function is essential for glaucoma research.

Purpose of the Study:

• To elucidate the distinct actions of cGMP on the ciliary epithelium.
• To investigate the mechanisms underlying cGMP's effects on ion transport.
• To explore potential interactions between cGMP and cAMP signaling pathways.

Main Methods:

• Isolated rabbit and cat ciliary epithelia were used to measure short-circuit current (ISC).
• cGMP, atrial natriuretic peptide (ANP), and sodium nitroprusside were applied to aqueous and stromal surfaces.
• Ion channel blockers (Ba2+, bumetanide, DIDS) and pump inhibitors (strophanthidin) were employed.
• Whole-cell patch clamping of cultured human nonpigmented ciliary epithelial (NPE) cells was performed.

Main Results:

• Aqueous cGMP reduced ISC in both rabbit and cat ciliary epithelia.
• Stromal cGMP stimulated ISC in rabbit but had no effect in cat ciliary epithelia.
• Stromal cGMP's effect in rabbits involved K+ channels in pigmented epithelial (PE) cells.
• Aqueous cGMP's effect was not mediated by K+ or Cl- channels and involved Na+, K(+)-exchange pumps.
• Forskolin potentiated the response to aqueous cGMP, suggesting cAMP interaction.

Conclusions:

• cGMP exerts dual actions on the ciliary epithelium.
• A primary role of cGMP is to reverse cAMP-mediated inhibition of NPE Na+ pumps.
• A secondary action of cGMP involves enhancing K+ channel and pump activity in rabbit PE cells.