Effects of platelet-derived growth factor on Ca in 3T3 cells

The effect of platelet-derived growth factor (PDGF) on cellular Ca²⁺ was examined in BALB/c-3T3 cells. PDGF induced:

1. 1. A decrease in cell ⁴⁵Ca²⁺ content.

2. 2. An apparent increased rate of efflux of preloaded ⁴⁵Ca²⁺.

3. 3. A decrease in residual intracellular ⁴⁵Ca²⁺ remaining after rapid efflux.

4. 4. When added after the rapid phase of efflux of ⁴⁵Ca²⁺ had occurred, an immediate decrease in post-efflux residual intracellular ⁴⁵Ca²⁺.

All of the observed changes in ⁴⁵Ca²⁺ induced by PDGF are consistent with a rapid release of Ca²⁺ from an intracellular Ca²⁺ pool that has the slowest efflux and is relatively inaccessible to extracellular EDTA. When incubated with chlortetracycline (CTC), a fluorescent Ca²⁺ probe, 3T3 cell mitochondria became intensely fluorescent. Addition of PDGF resulted in a rapid decrease in CTC fluorescence intensity in both adherent and suspended 3T3 cells. The effects of PDGF on 3T3 cell Ca²⁺ stores and CTC fluorescence intensity were identical with the effects of the Ca²⁺ ionophore A23187 and of the proton ionophore carbonyl cyanide m-chlorophenyl hydrazone. Serum, which contains PDGF, also altered intracellular Ca²⁺ stores, but platelet-poor plasma, which does not contain PDGF, had no effect. EGF, insulin, and tetradecanoyl phorbol acetate (TPA), other factors which stimulate 3T3 cell growth, did not alter 3T3 cell Ca²⁺ stores. Release of Ca²⁺ from intracellular sequestration sites may be a mechanism by which PDGF Stimulates Cell growth.