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. 2016 Jul 26;111(2):294–300. doi: 10.1016/j.bpj.2016.06.015

Figure 3.

Figure 3

Intracellular Ca2+ signals evoked by stimulating neuronal purinergic receptors with ATP, ATP·Mg, ATP·Li, and ATP·Mg·Li. (A) Schematic representation of purinergic receptors on the cell surface: P2X receptors are ion channels that permit influx of Ca2+ ions when activated by purinergic ligands like ATP; P2Y receptors are G-protein-coupled and trigger Ca2+ release from intracellular stores when activated by ATP. (B) Ca2+ signals are reliably triggered by consecutive 20 s pulses of 100 μM ATP. Repeated responses in the same cell are not significantly different (compare 1st and 2nd responses: t100-20 = 114, 112 s, respectively, p = 0.83, n = 9). (C) Ca2+ signals elicited by 20 s pulses of 100 μM ATP·Mg, 100 μM ATP, or 100 μM ATP·Li. ATP·Li without Mg2+ lengthens the Ca2+ response by 39% (compare 2nd and 3rd responses (ATP vs. ATP·Li, [Mg2+] = 0 mM): mean t100-20 = 139, 193 s, respectively, p = 0.015, n = 12). (D) Ca2+ responses evoked by 20 s pulses of 100 μM ATP·Mg or 100 μM ATP·Mg·Li. Response evoked by ATP·Mg·Li was longer than that evoked by ATP·Mg by 2.2-fold (compare 1st and 2nd responses (ATP·Mg vs. ATP·Mg·Li): t100-20 = 86, 191 s, respectively, p = 2.4 × 10−5, n = 20; compare 1st and 3rd response (1st ATP·Mg vs. 2nd ATP·Mg; internal control): t100-20 = 86, 88 s, respectively, p = 0.78, n = 20). (E) Ca2+ responses triggered by 100 s pulses of 100 μM ATP·Mg or 100 μM ATP·Mg·Li in Ca2+-free buffer. The P2Y component of ATP response does not depend significantly on Li+ (compare 1st and 2nd responses (ATP·Mg vs. ATP·Mg·Li): t100-20 = 41, 50 s, respectively, p = 0.17338, n = 28; compare 1st and 3rd responses (1st ATP·Mg vs. 2nd ATP·Mg; internal control): t100-20 = 41, 38 s, respectively, p = 0.73, n = 28). In panels B–D, extracellular Ca2+ was 2.5 mM. Application of Li+ alone elicited no response (not shown).