1,4‐Dihydropyridine receptor associated with Ca2+ channels in human embryonic fibroblasts

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Abstract
By using the radioactively labeled 1,4-dihydropyridine (DHP) probe, [3H]PMD, we have demonstrated that cultured human embryonic fibroblasts grown at a low density in Eagle's medium supplemented with serum contain a single class of non-interacting DHP binding sites (B max, 1.2±0.3 pmol/ 106 cells; K d, 3.9 nM). After inhibition of the DHP receptor biosynthesis by cycloheximide, the number of [3H]PMD binding sites is reduced with a half-time of 12 h, which implies a turnover rate of 30 000±7500 receptors/h per cell. With progression to confluency, the B max value decreased up to 0.28±0.08 pmol/106 cells without significant change in K d value. When cells were grown at a low density in serum-free conditions, the number of [3H]PMD binding sites gradually increased 1.9-fold within 3 days. Addition of serum reversed this effect with the same time course. These results imply that the DHP-sensitive Ca2+ channels are involved in the control of the proliferation of human embryonic fibroblasts.