Hyposmotic Stress‐induced Cytoplasmic Calcium Increase Involves TRPV4 and Src Family Kinase Activation

Abstract

Many cells respond to osmotic stress by releasing ATP that acts as an extracellular signal for purinergic receptors. Receptor‐triggered increases of calcium and activation of Src family tyrosine kinases (SFKs) have previously been observed in lens epithelium. Here we examined the effect of hyposmotic stress on cytoplasmic calcium [(Ca2+)i] response.Hyposmotic solution caused an immediate increase in (Ca2+)i. The selective Src Family Kinase (SFK) inhibitor PP2 suppressed the calcium increase. Hyposmotic solution was found to cause SFK activation which is significantly suppressed by RN 1734, a selective TRPV4 antagonist. The hypotonicity‐induced (Ca2+)i increase also was prevented by RN 1734 or HC 067047. TRPV4 agonist, GSK1016790A or 4á‐PDD caused similar increase in (Ca2+)i as that caused by hyposmotic stress. Expression of TRPV4 was confirmed by western blot. Pertussis toxin pretreatment for 24h blocked the calcium response. The calcium response points to the involvement of P2‐purinoceptors and G protein. Consistent with this notion, intact lenses released ATP when exposed to hyposmotic solution.The results suggest that the hyposmotic stress‐induced (Ca2+)i increase is the result of an interaction between purinergic P2 receptors and SFK. TRPV4 activation induced calcium entry could be the early mechanism for the complex signaling pathways in the lenses response to osmotic stress.