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P2 purinergic receptor-coupled signaling in the rabbit ciliary body epithelium
Nasser A Farahbakhsh1, Marianne C Cilluffo
1Department of Physiological Science, 3817 Life Sciences, University of California-Los Angeles, Los Angeles, CA 90095-1606, USA. nasserf@lifesci.ucla.edu
Purpose:
To identify and characterize P2 purinergic receptors and their signaling pathways in the epithelial cells of the rabbit ciliary body.
Methods:
Real-time fluorescence ratio imaging of the intact fura-2-loaded nonpigmented ciliary body epithelial (NPE) cells of rabbit were used to record changes in the intracellular free calcium concentration ([Ca(2+)](i)), in response to a number of purinergic agonists and antagonists. The effects of some of these drugs on the inositol phosphate (IP) levels in ciliary processes were also examined.
Results:
Adenosine diphosphate (ADP), adenosine triphosphate (ATP), and uridine triphosphate (UTP) dose dependently increased the [Ca(2+)](i) and IP levels. The [Ca(2+)](i) increases induced by ADP and UTP were distinguishable, both kinetically and pharmacologically. The effect of ADP on [Ca(2+)](i) was mimicked by a number of P2Y(1)-selective agonists, and was blocked by three P2Y(1)-receptor-specific antagonists. The [Ca(2+)](i) increases elicited by ADP (or its analogs) and UTP were additive.
Conclusions:
Rabbit ciliary body epithelium possesses both P2Y(1) and P2Y(2) metabotropic purinergic receptor subtypes, which differentially use the IP(3)/Ca(2+) second-messenger pathway.