Secretion of immunoreactive ANF from FRTL-5 rat thyroid cells: regulation by calcium ionophore A23187.
Atrial natriuretic factor-like immunoreactivity (ir-ANF) was characterized in a continuous line of rat thyroid follicular cells (FRTL-5) and the influence of the calcium ionophore A23187 on ir-ANF secretion was examined. Ir-ANF was identified by immunohistochemical staining as primarily reticular and juxtanuclear in short-term cultures, and more peripheral and granular in longer-term cultures, suggesting a process of ir-ANF packaging into secretory granules. The accumulation of ir-ANF granules was dependent upon the presence of thyrotropin (TSH) in the medium. Secreted ir-ANF was characterized using reversed-phase, high-performance liquid chromatography (RP-HPLC) and radioimmunoassay as a single peak eluting one fraction earlier than 125I-labeled rat ANF (99-126) (i.e., circulating atrial ANF) included as an internal standard. A23187 treatment of cells exhibiting primarily reticular ir-ANF caused a change to a pattern of more distinct, peripherally localized granules. This change occurred within 1 h after A23187 treatment and was dependent on the presence of Ca2+ in the medium. In cultures containing primarily ir-ANF granules, A23187 (0.5 micrograms/ml) induced a peripheral translocation of the granules at 30 min and a complete degranulation by 7 h. Enzyme-linked immunoadsorbent assay (EIA) confirmed a dose-dependent effect of A23187 on ir-ANF release into the medium. These results suggest that some of the effects of Ca2+ in the thyroid could be ascribed to its mobilization and release of ir-ANF, which in turn may have autocrine effects on thyroid follicular cells.
D000818:Animals; D009320:Atrial Natriuretic Factor / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015550:Cell Degranulation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D007150:Immunohistochemistry; D009638:Norepinephrine / Q000494:pharmacology; D011863:Radioimmunoassay; D051381:Rats; D013194:Staining and Labeling; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism* / Q000502:physiology
D000001:Calcimycin; D009320:Atrial Natriuretic Factor; D002118:Calcium; D009638:Norepinephrine