ATP-induced [Ca²⁺]_i changes in the human corneal epithelium

Abstract

ATP, when leaked from damaged cells, is capable of eliciting responses in neighboring cells. A better understanding of the mechanism of this response is essential for designing therapeutic strategies for disease, there have been only a limited number of studies on the effect of ATP on the human cornea. We examined ATP-induced intracellular Ca²⁺ ([Ca²⁺]_i) changes in the human corneal epithelia, cultured to near confluence. Cells were loaded with the Ca²⁺ indicators, Indo-1 or Fluo-4, and [Ca²⁺]_i was monitored. ATP was found to induce an increase in [Ca²⁺]_i, which was initiated from the perinuclear region and the nuclear envelope per se, and then propagated gradually towards the periphery. Intranuclear Ca²⁺ was momentarily increased. UTP elicited an identical response, but adenosine and α, β-methylene ATP had no effect. Pretreatment with U73122 or thapsigargin inhibited the ATP-induced increase in [Ca²⁺]_i. When a cell was topically stimulated with ATP, the [Ca²⁺]_i increase spread beyond the cell boundary. The intercellular communications that accompanied the [Ca²⁺]_i changes were inhibited by octanol. We conclude that extracellular ATP in the human cornea caused the mobilization of Ca²⁺ from intracellular Ca²⁺ stores (e. g. the endoplasmic reticulum and nuclear envelope) via P2Y purinoceptors of the epithelial cell. The response to ATP appears to spread to neighboring regions through gap junctions in the epithelium.