Sensitivity and Specificity of oscs

Sensitivity and Specificity of Ca²⁺ Oscillations
Airway epithelial cells in culture displayed a wide range of sensitivities to extracellular ATP. This sensitivity is based on the Ca²⁺ response and can be classed in to three groups: low, intermediate and high sensitivity.
Low Sensitivity Cells: 5 uM ATP invokes only an initial Ca²⁺ transient (below, left, top trace). However, increasing doses of ATP, up to 100 uM, can evoke Ca²⁺ oscillations. The frequency of the oscillations increases with ATP concentration.		High Sensitivity Cells: A similar range of Ca²⁺ responses were observed in the high sensitivity cells. However, in these cells, the basic response of a single Ca²⁺ spike was evoked by 0.1 uM ATP while the fastest Ca²⁺ oscillations were evoked by 1 uM ATP. ATP doses of > 5 uM induced a plateau increase in Ca²⁺ .


Sensitivity to ATP and UTP Airway epithelial cells show similar Ca²⁺ responses to extracellular UTP. However, for all the cells examined, individual cells were more sensitive to UTP than ATP. The graph (right) shows the responses of 3 different cells to 0.1 uM UTP (Red trace) or ATP (Yellow trace). In a low sensitivity cell (top) UTP, but not ATP, induced a single Ca²⁺ spike. In an intermediate sensitivity cell (middle), UTP induced a single Ca²⁺ oscillation while ATP induce only a Ca²⁺ spike. In a high sensitivity cell (bottom), UTP induced Ca²⁺ oscillations with a frequency greater than those induced by ATP.
Conclusion The Ca²⁺ responses induced in airway epithelial cells by ATP and UTP and the greater sensitivity of these responses to UTP as compared to ATP suggests that the Ca²⁺ responses are mediated via a P2U receptor.