Figure 7.

The effect of extracellular apyrase on changes of [Ca²⁺]_i of HeLa control cells in response to agonists. (A) In the absence of apyrase, fura-2–loaded HeLa control cells respond to 50 μM ATP, added at t = 0 and present throughout the experiment, with an initial Ca²⁺ increase followed by Ca²⁺ oscillations. Time scale bar is indicated at the bottom of the figure. (B) In the presence of 40 IU/ml apyrase, the [Ca²⁺]_i increase in response to 50 μM ATP is completely abolished. (C) In the absence of apyrase, HeLa control cells also respond to the continuous presence of 100 μM histamine with an initial [Ca²⁺]_i peak followed by oscillatory changes of [Ca²⁺]_i. (D) In the presence of 40 IU/ml apyrase, the [Ca²⁺]_i responses to 100 μM histamine are unchanged. The changes in [Ca²⁺]_i are represented in arbitrary values.