Regulation of parathyroid hormone release by protein kinase-C is dependent on extracellular calcium in bovine parathyroid cells.
The purpose of this study was to evaluate regulation of PTH secretion by protein kinase-C (PKC) in adult bovine parathyroid cells. Extracellular calcium (Ca2+e) is the main physiological regulator of PTH secretion. Putative second messengers include intracellular calcium (Ca2+i), cAMP, inositol trisphosphate, and diacylglycerol (DAG). Both DAG and Ca2+i activate PKC. Certain phorbol esters mimic the effect of DAG and cause prolonged stimulation of PKC. The stimulatory phorbol esters 12-O-tetradecanoylphorbol acetate (1 microM) and phorbol-12,13-dibutyrate (1 microM) did not affect PTH secretion at low Ca2+e, but increased both individual cell secretion and recruitment of cells to secrete at high Ca2+e. The PKC inhibitors H7 (1 microM), tamoxifen (10 microM), and sphinganine (5 microM) inhibited PTH release at low Ca2+e (0.1 and 0.2 mM) and decreased cell recruitment over the physiological range of Ca2+e. The nonstimulatory phorbol esters 4 alpha-phorbol-12,13-didecanoate (1 microM) and phorbol-13-monoacetate (1 microM) had no effect on PTH secretion. To assess the mechanism by which certain phorbol esters stimulated PTH secretion, in situ hybridization for PTH mRNA was performed. Phorbol-12,13-dibutyrate (1 microM) qualitatively increased steady state PTH mRNA levels compared to control values. We conclude that 1) PKC stimulation increased PTH secretion at high Ca2+e, but not at low Ca2+e; 2) PKC inhibition decreased PTH secretion at low Ca2+e; and 3) PKC stimulation increased steady state PTH mRNA levels. These data suggest that PKC plays an important regulatory role in the synthesis and secretion of PTH.
Clarke
B L
BL
Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota.
Hassager
C
C
Fitzpatrick
L A
LA
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D017403:In Situ Hybridization; D007700:Kinetics; D010280:Parathyroid Glands / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010281:Parathyroid Hormone / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology; D013629:Tamoxifen / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D010281:Parathyroid Hormone; D012333:RNA, Messenger; D013629:Tamoxifen; D011493:Protein Kinase C; D013110:Sphingosine; D013755:Tetradecanoylphorbol Acetate; C005682:safingol; D002118:Calcium