Free intracellular Ca2+ concentration ([Ca2+]i) and growth hormone release from purified rat somatotrophs. II. Somatostatin lowers [Ca2+]i by inhibiting Ca2+ influx
| Autor: | M.B. French, J. Kraicer, B. C. Moor, D.A. Wood, B.T. Lussier |
|---|---|
| Rok vydání: | 1991 |
| Předmět: |
Male
medicine.medical_specialty Indoles Somatotropic cell chemistry.chemical_element Neuropeptide Biological Transport Active Stimulation Cell Separation Calcium Biology Endocrinology Pituitary Gland Anterior Internal medicine medicine Centrifugation Density Gradient Animals Cells Cultured Fluorescent Dyes Rats Inbred Strains Rats Somatropin Kinetics Somatostatin Spectrometry Fluorescence chemistry Growth Hormone Second messenger system Intracellular |
| Zdroj: | Endocrinology. 128(1) |
| ISSN: | 0013-7227 |
| Popis: | This study was carried out to investigate the role of Ca2+ in the somatostatin (SRIF)-induced inhibition of GH release. We examined the effect of SRIF on basal and GH-releasing factor (GRF)-induced increases in Ca2+ influx and free intracellular Ca2+ concentration ([Ca2+]i) in normal somatotrophs and examined the effect of SRIF on 45Ca uptake, [Ca2+]i measured with indo-1, and GH release. SRIF inhibited basal and GRF-induced GH release concurrently with a reduction in steady state 45Ca uptake. In nonsteady state experiments, SRIF also decreased basal 45Ca uptake. SRIF decreased baseline [Ca2+]i in a concentration-dependent manner and inhibited the GRF-induced biphasic increase in [Ca2+]i, but in a differential fashion. Low concentrations of SRIF abolished the peak (first phase) without affecting the plateau (second phase), while at high concentrations, both phases were inhibited. SRIF blocked the GRF-induced increase in [Ca2+]i regardless of whether it was applied before or during GRF stimulation. These data indicate that the SRIF-dependent decrease in 45Ca uptake is due to a decrease in Ca2+ influx. This is further supported by the fact that the GRF-dependent increase in [Ca2+]i, which is dependent on Ca2+ influx, is blocked by SRIF. The reported ability of SRIF to reduce the activation rate of Ca2+ currents, decrease Ca2+ conductance, and hyperpolarize the cell would explain the differential effect of SRIF on the GRF-induced [Ca2+]i increase. The inhibitory effect of SRIF on GH release would then be dependent on the ability of SRIF to decrease, or prevent, an increase in [Ca2+]i. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|