Local detection of mechanically induced ATP release from bone cells with ATP microbiosensors.

The mechanically induced release of adenosine-5'-triphosphate (ATP) from osteoblastic cells (MC3T3-E1) was measured in real time. A stretching device integrated into scanning electrochemical microscopy was developed to apply controlled mechanical strain to MC3T3-E1 cells. For ATP secretion, a stepwise yet uniform mechanical stress was imposed onto MC3T3-E1 cells. The ATP biosensors were positioned at a distance of approximately 30-40 μm above the cell surface. Calibration functions were recorded prior to the cell measurements and revealed a linear response up to 40 μM with a sensitivity of 1-5pA/μM ATP. Stretching MC3T3-E1 cells up to 21% resulted in a concentration of 30.57±4.82 μM of extracellular ATP (N=12) detected above the cell surface. As a control experiment, nifedipine, a L-type voltage sensitive calcium channel (L-VSCC) inhibitor was applied, which blocks Ca(2+)entry from the outer medium into the cell. Inhibition resulted in a significantly smaller amount of released ATP, i.e., 7.08±1.93 μM ATP (N=10). Further control experiments with glucose microbiosensors did not yield significant changes of the baseline current (N=8).