[PDGF-induced effect on cytosolic free calcium concentration of cultured retinal pericytes]

Although the selective loss of retinal pericytes has long been known to be one of the earliest histopathological findings in diabetic retinopathy, only limited information is available concerning their function and cell biology. Recently, it has been shown that the interaction of endothelial cells and pericytes plays an important role in the maintenance of vascular integrity. Additionally, it has been suggested that pericytes have a contractile function. Platelet-derived growth factor (PDGF), released from endothelial cells, has been shown to be a potent mitogen and vasoconstrictor. Cytosolic free calcium ([Ca2+]i) has been shown to play a key role as a second messenger for PDGF, involved in the regulation of various cellular functions, e.g. cell proliferation and vascular contractility. In order to characterize the effect of different PDGF homodimers on cultured bovine retinal pericytes, we investigated PDGF-AA- and -BB-dependent alterations in [Ca2+]i was determined with the Ca(2+)-sensitive fluorescent probe Quin-2. Basal levels were 118 +/- 30 nM. Stimulation with PDGF-BB in concentrations ranging from 5 to 20 ng/ml led to a dose-dependent increase of [Ca2+]i with an EC50 of 5.8 ng/ml. Maximum stimulation, to about 280% of basal levels, occurred after 3-4 min. In contrast, PDGF-AA was not effective. The results suggest that PDGF-BB may influence the integrity and contractility of the retinal microvasculature via modulation of the intracellular calcium homeostasis of pericytes. Additionally, it can be speculated that cultured retinal pericytes express mainly PDGF-beta-type receptors.