Figure 4. Ca²⁺ increase in OPC processes is mediated by glutamate and ATP released in response to action potentials in axons.

(a) Representative Ca²⁺ traces in OPC processes in response to electrical stimulation of axons without (black) and with (blue) BoNT/A treatment to block SNARE-dependent exocytosis. (b) Averaged Ca²⁺ traces in OPCs from 14 dishes are shown. Responses were inhibited by BoNT/A treatment. **P=0.001, t-test, peak amplitude, n=14 cells from 14 dishes with no BoNT/A, n=14 cells from 14 dishes with BoNT/A. (c) Number of Ca²⁺ responses were reduced significantly by BoNT/A treatment (blocked). The peak Ca²⁺ response within 200 s of axonal stimulation (10 Hz) were measured. P=0.004, t-test, n=14 cells from 14 dishes with no BoNT/A, n=14 cells from 14 dishes with BoNT/A. (d) Summary graph shows per cent inhibition of Ca²⁺ responses following treatment with selective blockers of glutamatergic and purinergic neurotransmitter receptors, including a combination of CNQX, DAPV, MCPG (GluR antagonists), suramin and MCPG. The results implicate both glutamate and ATP neurotransmitter signalling. P=0.3, n=6 cells from six dishes, *¹P=0.03, n=4 cells from four dishes, **P=0.008, n=5 cells from five dishes, *²P=0.02, n=6 cells from six dishes, all paired t-test.