Figure 7. Purinergic activation of Panx-1-like currents in type II cells is mediated by P2Y2 receptors in association with a rise in intracellular Ca²⁺.

A, both ATP and UTP (50 μm) induce inward currents (at −60 mV) of similar magnitude in the same type II cell as expected for P2Y2 receptors. B, dose–response relation for the UTP-evoked currents in a group of type II cells is shown by the black curve; data are represented as means ± SEM (n = 4) and fitted with the Hill equation with an EC₅₀ = 37 μm. The dose–response curve for ATP (red) from Fig. 4B is superimposed and is indistinguishable from that for UTP. C, intracellular Ca²⁺ responses monitored simultaneously in type I and type II cells located in different regions of the same culture. Note that both hypercapnia (10% CO₂) and the depolarizing stimulus high (30 mm) K⁺ induce robust Δ[Ca²⁺]_i responses in the type I cell (upper trace), but are ineffective in the two type II cells (lower traces). Conversely, ATP and UTP induced comparable robust Δ[Ca²⁺]_i responses in both type II cells, but not in the type I cell; small Ca²⁺ responses of unknown origin were sometimes seen in the type I cell after removal of each purine (upper trace). Period during which each stimulus was applied is indicated by the shaded vertical bars.