Optical and electrical recording techniques were applied to single primary pituitary cells to characterize the types of voltage-dependent calcium currents (Icaand levels of intracellular calcium ([Ca2+]i. GH-containing somatotrophs and PRL-containing lactotrophs were isolated from adult female rats using fluorescence-activated cell-sorting techniques and were maintained in culture for 1� 4 days. Whole cell patch-clamp recordings were made to analyze the Ica, and [Ca2+]iwas measured with fura-2. Cell type was verified after each recording by indirect immunocytochemistry. GH and PRL cells could be divided into two groups: silent and spontaneously active. Silent cells had stable membrane potentials and stable levels of [Ca2+]i. Spontaneously active cells exhibited spontaneous action potentials and large fluctuations in [Ca2+]i. Two types of ICawere found: a low threshold, transient current which was insensitive to the dihydropyridine � Bay 5417 (the negative isomer of Bay K 8644), and a high threshold, sustained current which was enhanced by � Bay 5417. Both types of Icawere present in PRL and GH cells, but each cell type differed quantitatively in the proportion of each current type. While the GH cells had a more prominent, low threshold, transient Ica, the PRL cells had a more prominent, high threshold, sustained Ica- The enhancement of Icaby � Bay 5417 was greater in the PRL cells, which have a larger dihydropyridine-sensitive Ica. Parallel fura-2 measurements showed an increase in [Ca2+]i in response to 50 mM KC1 and � Bay 5417 for both lactotrophs and somatotrophs.
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