Comparison of lactotrope subtypes of neonatal and adult male rats: plaque assays and patch-clamp studies.

We examined the differences in lactotrope number and function between pituitary cultures from neonatal (10-day-old) and adult male rats. Basal hormone release was measured with the reverse hemolytic plaque assay. Whole cell Ba2+ currents through Ca2+ channels were recorded from identified prolactin (PRL) secretors with the patch-clamp technique. Lactotropes were classified in two groups according to the relative amount of PRL released: small-plaque (SP) secretors accounted for 6% of all cells in both neonatal and adult pituitary cultures, whereas large-plaque (LP) secretors comprised 13% of the adult pituitary cells but were scarce in cultures from neonates. Simultaneous plaque assays for PRL and growth hormone (GH) showed that in adults as well as in neonates the number of SP and LP secretors was similar to the number of lactosomatotropes (PRL cells that also release GH) and classical lactotropes (PRL-only cells), respectively. Ba2+ current density at positive membrane potentials was markedly higher in a...