sentence: The dissociation between the time-course of ATP and hormone accumulation in the medium from GH cells indicates that ATP release occurs through either a pathway other than the exocytotic , or that ATP , but not PRL , is degraded and therefore a progressive decrease in extracellular ATP concentrations in static cultures after replacement of medium reflects the time needed to reach a balance between ATP release and its degradation by ectonucleotidases.In additional experiments aimed to further exclude the possible impact of lysis of cells on ATP release , GT1-7 , α T3-1 and GH cells were attached on beads and perifused for 150 min with ATP-free buffer at flow rate of 0.8 ml / min , prior to sample collection for ATP measurements .