28 October 1998
Basic fibroblast growth factor (bFGF) exerts angiogenic and mitogenic properties in human tissue. Since changes in ion currents modulate essential Ca<sup>2+</sup>-dependent intracellular pathways in endothelial cells, we have investigated a possible contribution of Ca<sup>2+</sup>-activated K<sup>+</sup> channels (BK<sub>Ca</sub>) on bFGF-induced endothelial cell proliferation. The patch-clamp technique was used to identify BK<sub>Ca</sub> and to study their modulation by bFGF in cultured endothelial cells of human umbilical cord veins (HUVEC). Cell counts of HUVEC were carried out on different days to analyze bFGF-induced cell proliferation and its influence by the specific BK<sub>Ca</sub> blocker iberiotoxin (IBX). Using single-channel recordings, we found characteristic BK<sub>Ca</sub> with a single-channel slope conductance of 170.3 ± 2.1 pS (n = 7), half-maximal activation at internal pCa = 5.7 (n = 5; test potential: 80 mV), and dose-dependent block by IBX (25–100 nmol/l). In cell-attached patches bFGF (50 ng/ml) caused a significant increase in the open-state probability (NPo) after 6 min at test potentials of 80 and 100 mV (n = 28; p < 0.001), respectively, which lasted up to 30 min. After preincubation with pertussis toxin (100 ng/ml; 4 h) bFGF superfusion did not cause a significant increase in BK<sub>Ca</sub> activity until 25 min had passed (n = 20; p < 0.01). Addition of 100 nmol/l IBX to the pipette solution caused a total block of BK<sub>Ca</sub> within 2 min in cell-attached patches, whereas bFGF (50 ng/ml) was not able to activate BK<sub>Ca</sub>. When incubated with IBX (25–100 nmol/l) every 2 days, bFGF-induced proliferation of HUVEC was significantly decreased by 50 (–41%) and 100 nmol/l (–50%) IBX (n = 5; p < 0.001) after 7 days. We conclude that activation of BK<sub>Ca</sub> by bFGF may play an important role in bFGF-induced proliferation of human endothelial cells and thus might be important in the process of angiogenesis and vascular remodelling.