The [Ca²⁺]_i increase induced in murine thymocytes by extracellular ATP does not involve ATP hydrolysis and is not related to phosphoinositide metabolism

Abstract

We have previously demonstrated that exogenous ATP can give medullary thymocytes the calcium message required for the induction of their blastogenesis. In the present study, using the highly sensitive calcium indicator Indo-1, we have measured the effect of exogenous nucleotides on the cytosolic-free calcium concentration [Ca"]i of thymocytes, and determined inositol phosphate (IP) formation in the same cells, in parallel assays. The results were compared to those obtained with the mitogenic lectin concanavalin A (ConA) in similar experiments. They show that ATP does not mobilize calcium from its internal stores but stimulates its influx from the extracellular medium. Nevertheless, these data do not rule out the possibility that the nucleotide acts through specific P2 purinergic sites.

Extracellular ATP causes lysis of mouse thymocytes and activates a plasma membrane ion channel

“…Furthermore, the channel(s) of lymphocytes also differed from those described by Buisman et al in macrophages [16] and by Tatham & Lindau in mast cells [17], having a much lower Mr cut-off. Finally, in thymocytes, in contrast with reports on other cell types [18][19][20][21], ATP0 was unable to generate InsP3 and mobilize Ca2+ from intracellular stores [22], thus suggesting a direct coupling of the ATPO receptor to the channel(s). However, a rise in [Ca21]i was not required for lysis, thus indicating that ATPO activates a Ca2+-independent lytic pathway in mouse thymocytes.…”

“…Some agents known to block Ca2+ fluxes through receptoroperated channels (ROCs) or voltage-operated channels (VOCs) [18,19], influx of Ca2+ from the extracellular medium [18,22], generation of InsP3 [21], and uptake of extracellular aqueous solutes of Mr up to 900 [12,14]. Vol.…”

The effects of Bay K 8644 and nifedipine on the responses of rat urinary bladder to electrical field stimulation, β,γ‐methylene ATP and acetylcholine

“…In the dog mesenteric artery, nifedipine can selectively inhibit the purinergic component of the contractions evoked by sympathetic nerve stimulation (Omote et al, 1989), and in snail neurones nanomolar concentrations of extracellular ATP can activate membrane calcium channels (Yatani et al, 1982). Also, P2-purinoceptor-mediated calcium mobilization across the cell membrane has been observed in rat isolated alveolar type II cells (Dorn et al, 1989), murine thymocytes (El-Moatassim et al, 1989), human promyelocyteic cell line HL60 (Nonotte et al, 1989), Ehrlich ascites tumour cells (Dubyak & De Young, 1985), pancreatic i-cells (Gylfe & Hellman, 1987) and rat parotid acinar cells (McMillian et al, 1987).…”

Extracellular ATP-induced acidification leads to cytosolic calcium transient rise in single rat cardiac myocytes

“…This rise in [Ca21]i is associated with biphasic changes in cytoplasmic pH in endothelial cells [13]. Furthermore, in the same study, it was shown that the nucleotide also increased membrane ionic permeabilities as well as it does in thymocytes [14] and in macrophages [15]. More particularly, ATP activates a cationic conductance in cultured muscle cells [16][17][18], in smooth-muscle cells [19,20] and in lacrimal acinar cells [21].…”