Platelet-derived growth factor effects on purified testicular peritubular myoid cells: binding, cytosolic Ca++ increase, mytogenic activity, and extracellular matrix production enhancement

The response of purified rat testicular peritubular myoid cells (PMC) to platelet-derived growth factor (PDGF) was studied. Freshly isolated PMC were devoid of measurable amounts of PDGF-binding sites. However, after 1 day in culture in serum-free conditions, specific high affinity receptors were detected. The estimated binding sites per cell revealed that PMC express more receptors for PDGF-BB, followed by PDGF-AB and PDGF-AA. PDGF treatment of cultured PMC increased the cytosolic Ca2+ concentration, showing a rank order of potencies with PDGF-BB > PDGF-AB > PDGF-AA. PMC proliferation, as measured by direct cell counting, was also stimulated by all three PDGF isoforms, with the same order of potencies observed for the increase in intracellular Ca2+. This effect was inhibited by antibodies to PDGF. Moreover, PDGF treatment increased the release of type IV collagen and fibronectin, and induced the release of type V collagen and laminin. These results demonstrate that testicular PMC are induced to express functionally active PDGF receptors in response to cell culturing. These data suggest that PMC may be a target for PDGF and that PDGF-mediated effects in vivo are dependent on factors regulating the expression of the receptors. The role that PDGF may play in normal and pathological testicular processes is discussed.