Purinergic receptors in ocular ciliary epithelial cells

Area of Science:

• Pharmacology
• Cell Biology
• Ophthalmology

Background:

• Purinergic receptors, specifically P1 for adenosine and P2 for adenosine triphosphate (ATP), mediate cellular responses.
• Ciliary epithelium cells play a crucial role in ocular physiology and are potential targets for purinergic signaling.

Purpose of the Study:

• To pharmacologically characterize P1 and P2 purinergic receptor-mediated signal transduction in cultured human nonpigmented ciliary epithelium (NPE) and bovine pigmented ciliary epithelium (PE) cell lines.
• To elucidate the specific subtypes and signaling mechanisms of adenosine and ATP receptors in these ocular cells.

Main Methods:

• Cultured NPE and PE cell lines were utilized for pharmacological studies.
• Adenylate cyclase activity was measured in response to various adenosine receptor agonists and antagonists.
• Inositol phosphate production was assessed to characterize P2 receptor activity using ATP analogues.

Main Results:

• Adenosine exhibited dual effects on adenylate cyclase, inhibiting at high potency (nanomolar) and stimulating at low potency (micromolar), indicating the presence of P1 receptor subtypes.
• Selective P1 agonists like cyclopentyladenosine (CPA) and 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamido adenosine (CGS 21680) modulated adenylate cyclase activity with specific potencies in NPE and PE cells.
• Characterization of P2 receptors revealed the presence of a putative P2u receptor in both NPE and PE cells, evidenced by stimulated inositol phosphate production in response to ATP and its analogues.

Conclusions:

• Both human NPE and bovine PE cell lines express functional P1 and P2 purinergic receptors.
• The identified P1 receptor subtypes mediate distinct signaling pathways involving adenylate cyclase inhibition and stimulation.
• The presence of a P2u receptor suggests a role for ATP in regulating cellular functions within the ciliary epithelium.