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Interaction between mitogens upon intracellular Ca2+ pools in murine fibroblasts
M G Cattaneo1, L Magrini, S B Sparber
1Department of Pharmacology, University of Milan, Italy.
Abstract:
A comparison of the effect of platelet-derived growth factor (PDGF) and bombesin on intracellular Ca2+ stores was carried out in Swiss 3T3 cells loaded with Fura-2. It was found that the tumor promoter thapsigargin (Tg) almost completely inhibited both the PDGF- and the bombesin-induced intracellular Ca2+ concentration ([Ca2+]i) rise, indicating that the two mitogens mobilize Ca2+ from intracellular pool(s) sensitive to the tumor promoter. It was also found that pre-treatment with PDGF almost totally and persistently (up to at least 30 min) inhibited the bombesin-, Tg- and ionomycin-induced rise in [Ca2+]i, whereas pre-treatment with bombesin had only a partial inhibitory effect on the PDGF, Tg and ionomycin [Ca2+]i response, both in the absence and in the presence of external Ca2+. On the other hand, vasopressin and bradykinin, which also stimulate hydrolysis of phosphoinositides in these cells, did not affect the [Ca2+]i response induced by the same agents. These results indicate that, despite the poor production of inositol 1,4,5-trisphosphate (InsP3), PDGF was capable of totally discharging and maintaining discharged the InsP3-sensitive stores of intracellular Ca2+, regardless of whether extracellular Ca2+ was present in the medium. Bombesin only partially caused this effect. On the contrary, bradykinin and vasopressin, after releasing intracellular Ca2+ allowed an almost total refilling of the pools. It is interesting to note that, at variance with PDGF and bombesin, neither bradykinin nor vasopressin are able to induce a mitogenic response in Swiss 3T3 cells.
Insights
Platelet-derived growth factor (PDGF) and bombesin mobilize intracellular calcium, but PDGF persistently depletes calcium stores, unlike bombesin, vasopressin, or bradykinin in Swiss 3T3 cells.
Area of Science:
- Cellular Biology
- Molecular Signaling
- Calcium Homeostasis
Background:
- Platelet-derived growth factor (PDGF) and bombesin are mitogens that stimulate intracellular calcium release in Swiss 3T3 cells.
- Thapsigargin (Tg) is a tumor promoter that inhibits intracellular calcium stores.
Purpose of the Study:
- To compare the effects of PDGF and bombesin on intracellular calcium ([Ca2+]i) stores in Swiss 3T3 cells.
- To investigate the role of intracellular calcium pools sensitive to thapsigargin.
- To determine the impact of pre-treatment with mitogens on subsequent calcium responses.
Main Methods:
- Swiss 3T3 cells were loaded with Fura-2 to measure intracellular calcium concentration ([Ca2+]i).
- Cells were treated with PDGF, bombesin, thapsigargin (Tg), ionomycin, vasopressin, and bradykinin.
- Pre-treatment experiments were conducted to assess the inhibitory effects of PDGF and bombesin.
Main Results:
- Both PDGF and bombesin induced a rise in [Ca2+]i, which was inhibited by Tg, indicating mobilization from Tg-sensitive intracellular pools.
- PDGF pre-treatment almost completely and persistently inhibited bombesin-, Tg-, and ionomycin-induced [Ca2+]i rises.
- Bombesin pre-treatment had only a partial inhibitory effect, while vasopressin and bradykinin did not affect the [Ca2+]i response to these agents.
- PDGF, despite poor inositol 1,4,5-trisphosphate (InsP3) production, totally discharged InsP3-sensitive calcium stores, whereas bombesin only partially did so.
- Vasopressin and bradykinin released intracellular calcium and allowed pool refilling, unlike PDGF and bombesin, and do not induce mitogenesis.
Conclusions:
- PDGF and bombesin mobilize Ca2+ from intracellular stores sensitive to thapsigargin in Swiss 3T3 cells.
- PDGF has a potent and sustained effect on discharging intracellular calcium stores, independent of extracellular calcium.
- The differential effects of PDGF, bombesin, vasopressin, and bradykinin on calcium stores correlate with their mitogenic potential in Swiss 3T3 cells.