Figure 4. Effects of the removal of extracellular Ca²⁺ on the noradrenaline- and ATP-evoked [Ca²⁺]_i responses.

Periods of exposure to 1 μm noradrenaline (NA), 10 μm ATP and the nominally Ca²⁺-free bath solution (0 Ca²⁺) were indicated by the horizontal bars below the records. A, a single cell was exposed to noradrenaline in the standard bath solution ([Ca²⁺]_o= 2.0 mm) and in nominally Ca²⁺-free bath solution, as indicated. Note that noradrenaline evoked only a transient and small increase in [Ca²⁺]_i in the nominally Ca²⁺-free solution. B, the bath solution was changed to the nominally Ca²⁺-free solution with noradrenaline present. The noradrenaline-induced increase in [Ca²⁺]_i was nearly completely abolished in the absence of extracellular Ca²⁺. C, a single cell was stimulated with noradrenaline in standard bath solution and then with ATP in nominally Ca²⁺-free bath solution. Each trace is obtained from different cells and is representative of 6–8 cells.