Western blots showing tyrosine phosphorylation in control (lanes 1 to 4) and Scott erythrocyte ghosts (lanes 5 to 8) after a 15-minute incubation period with increasing concentrations of ATP: 0.05 mmol/L (lanes 1 and 5); 0.5 mmol/L (lanes 2 and 6); 1.0 mmol/L (lanes 3 and 7) and 2.0 mmol/L (lanes 4 and 8).