Our purpose was to elucidate how extracellular ATP causes cell death in the retinal microvasculature. Although ATP appears to serve as a vasoactive signal acting via P2X7 and P2Y4 purinoceptors, this nucleotide can kill microvascular cells of the retina. Because P2X7 receptor activation causes transmembrane pores to form and microvascular cells to die, we initially surmised that pore formation accounted for ATP’s lethality. To test this hypothesis, we isolated pericyte-containing microvessels from rat retinas and assessed cell viability by trypan blue dye exclusion, detected pores by the uptake of the fluorescent dye YO-PRO-1, measured intracellular calcium with the use of fura-2 and monitored ionic currents via perforated-patch pipettes. As predicted, ATP-induced cell death required P2X7 receptor activation. However, we found that pore formation was minimal because ATP’s activation of P2Y4 receptors prevents P2X7 pores from forming. Rather than opening lethal pores, ATP kills by a mechanism involving voltage-dependent calcium channels (VDCC’s). Our experiments suggest that when high concentrations of ATP cause nearly all microvascular P2X7 receptor/channels to open, the resulting profound depolarization opens VDCC’s
To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.