Author/Editor | Zorec, R; Sikdar, SK; Mason, WT | |
Title | Increased cytosolic calcium stimulates exocytosis in bovine lactotrophs. Direct evidence from changes in membrane capacitance | |
Type | članek | |
Source | J Gen Physiol | |
Vol. and No. | Letnik 97, št. 3 | |
Publication year | 1991 | |
Volume | str. 473-97 | |
Language | eng | |
Abstract | The patch-clamp technique has been used to measure changes in membrane capacitance (Cm) of bovine lactotrophs in order to monitor fluctuations in cell surface area associated with exo- and endocytosis. Cells were prepared by an enrichment procedure and cultured for up to 14 d before use. Under whole-cell recording, cell cytoplasm was dialyzed with various Ca2(+)-containing solutions. The resting Cm of 6.05 +/- 1.68 pF was found to correlate well with squared cell radius, suggesting a specific Cm of 0.8 microF/cm2. Discrete Cm steps of 2-10 fF were recorded, which most likely reflect single fusion and retrieval events of prolactin-containing granules (0.2-0.6 microns in diameter). High Ca2+ resulted in a Cm increase of 20-50 percent from the resting value, demonstrating a role for ŠCa2+Ći in stimulus-secretion coupling. Spontaneous Cm changes have also been recorded, which presumably reflect prolactin secretion supported by a tonic influx of Ca2+ through the membrane. This is supported by the following findings: addition of Co2+ diminished or reversed the spontaneous Cm changes and decreased resting ŠCa2+Ći; and membrane depolarization increased Cm, indicating the role of voltage-activated channels in stimulus-secretion coupling. As bovine lactotrophs have been found to be largely devoid of spontaneous electrical activity, a mechanism involving modulation of a tonic Ca2+ influx is proposed; this is shown to provide adequate control of basal and triggered secretion monitored by Cm. | |
Descriptors | CALCIUM CYTOSOL EXOCYTOSIS PITUITARY GLAND, ANTERIOR CYTOSOL ELECTROPHYSIOLOGY FURA-2 MEMBRANE POTENTIALS PITUITARY GLAND, ANTERIOR CATTLE COBALT |