Purinergic receptors in the rat lens: activation of P2X receptors following hyperosmotic stress.

PURPOSE A range of P2Y and P2X receptors is expressed in the rat lens. Because most P2X receptors are located in the cytoplasm, the authors sought to determine whether P2X receptors are functionally active. METHODS Rat lenses were cultured under either isotonic or hypertonic conditions in the presence of P2 receptor agonists or antagonists. Lenses were fixed and cryosectioned, cell membranes were labeled, and confocal microscopy was used to determine whether the different reagents affected cell morphology. RESULTS Application of the P2 receptor inhibitor PPADS to lenses cultured under isotonic conditions induced extracellular space dilations between fiber cells in a distinct zone in the outer cortex. This damage was not caused by the inhibition of P2X(1) or P2Y(1) because more selective antagonists for P2X(1) (MRS2159) and P2Y(1) (MRS2179) either did not cause any damage or induced extracellular dilations located between superficial fiber cells at the lens modiolus, respectively. Although the P2 agonists ATPgammaS and ADPbetaS both induced a distinctive disruption to cell morphology in the same localized zone as PPADS, the P2X-specific agonist alpha,beta-methyl-ATP induced no change to cell morphology. However, under hypertonic conditions that cause the insertion of P2X(1,4) into the membranes, alpha,beta-methyl-ATP induced a localized zone of damage that was associated with changes in actin distribution. CONCLUSIONS The results show that P2X receptors may play a minimal role in mediating ion fluxes in the rat lens under steady state conditions. In contrast, hypertonic cell shrinkage activates previously inactive P2X receptors in the lens, suggesting P2X receptors may play a role in the lens in response to osmotic stress.