Binding of (+)-PN 200-110 to rat pituitaries and to normal and adenomatous human pituitaries

Abstract Endocrine cells possess voltage-sensitive Ca 2+ channels involved in the modulation of hormonal secretion. Using the dihydropyridine, ( + )-PN 200−110, we have investigated the binding characteristics of this ligand to pituitary membrane Ca 2+ channels from normal rat, normal and adenomatous human pituitaries. [ 3 H]PN 200-110 binds specifically to rat pituitary membranes to one class of sites ( K d = 0.41 ± 0.10 nM; B max = 39 ± 1.3 fmol/mg protein). At 37°C, equilibrium is reached in 45 min and half-life of the binding is 13 min. No significant changes were observed for either the K d or B max values between normal rat and human pituitaries or between the different types of adenomas (GH- and PRL-secreting and non-secreting). As the secretory activity of the pituitary adenomas, involving Ca 2+ mobilization, varies from one adenoma to another, our results could indicate that, if there is a modified regulation of Ca 2+ entry in the adenomas, it may not be related to a varying number of calcium channels, at least the channels labeled by the dihydropyridine ( + )-PN 200-110.