Mobilization of intracellular calcium by substance p in a human astrocytoma cell line (U‐373 MG)

Variations in intracellular free calcium concentration (Δ[Ca 2+ ] i ) were measured in intact and isolated human astrocytoma cells (U373 MG) loaded with fura‐2 acetoxymethylester. Microperfusion of 50 nM substance P (SP), applied for 1 s, increased [Ca 2+ ] i by 351 nM from a stable basal level of [Ca 2+ ] i of 26 nM. The peak Δ[Ca 2+ ] i induced by SP was dose dependent with a threshold of 10 ‐3 nM, an ED 50 of 1.3 nM and a maximal effect for concentrations of SP greater than 100 nM. The NKI receptor agonist, [Sar 9 Met(O 2 ) 11 ]SP, mimicked the effect of SP, while the NK 2 and NK 3 selective receptor agonists, [N1 10 ]NKA(4‐10) and senktide, respectively, had no effect. The Δ[Ca 2+ ] i induced by SP was unaffected by 100 μM cadmium or by removal of extracellular calcium ions. Caffeine up to 30 mM had no effect on [Ca 2+ ] i . In contrast, thapsigargin increased resting [Ca 2+ ] i by 92 nM and reduced the Δ[Ca 2+ ] i induced by SP. A pertussis treatment (500 ng/ml‐24 h) did not modify the Δ[Ca 2+ ] i induced by SP. We conclude that SP, acting on a NK1 receptor, mobilizes cytosolic calcium from an intracellular calcium pool which can be partially depleted by thapsigargin. © 1994 Wiley‐Liss, Inc.