Abstract
The effects of epidermal growth factor (EGF) on intracellular calcium ([Ca2+](i)) responses to the muscarinic agonist carbachol were studied in a human salivary cell line (HSY). Carbachol (10-4 M)-stimulated [Ca2+](i) mobilization was inhibited by 40% after 48-h treatment with 5 x 10-10 M EGF. EGF also reduced carbachol-induced [Ca2+](i) in Ca2+-free medium and Ca2+ influx following repletion of extracellular Ca2+. Under Ca2+-free conditions, thapsigargin, an inhibitor of Ca2+ uptake to internal stores, induced similar [Ca2+](i) signals in control and EGF-treated cells, indicating that internal Ca2+ stores were unaffected by EGF; however, in cells exposed to thapsigargin, Ca2+ influx following Ca2+ repletion was reduced by EGF. Muscarinic receptor density, assessed by binding of the muscarinic receptor antagonist L-[benzilic-4,4'-3HCN]quinuclidinyl benzilate ([3H]QNB), was decreased by 20% after EGF treatment. Inhibition of the carbachol response by EGF was not altered by phorbol ester-induced downregulation of protein kinase C (PKC) but was enhanced upon PKC activation by a diacylglycerol analog. Phosphorylation of mitogen-activated protein kinase (MAP kinase) and inhibition of the carbachol response by EGF were both blocked by the MAP kinase pathway inhibitor PD-98059. The results suggest that EGF decreases carbachol-induced Ca2+ release from internal stores and also exerts a direct inhibitory action on Ca2+ influx. A decline in muscarinic receptor density may contribute to EGF inhibition of carbachol responsiveness. The inhibitory effect of EGF is mediated by the MAP kinase pathway and is potentiated by a distinct modulatory cascade involving activation of PKC. EGF may play a physiological role in regulating muscarinic receptor-stimulated salivary secretion.
Original language | English (US) |
---|---|
Pages (from-to) | C1024-C1033 |
Journal | American Journal of Physiology - Cell Physiology |
Volume | 279 |
Issue number | 4 48-4 |
DOIs | |
State | Published - 2000 |
Keywords
- Carbachol
- Epidermal growth factor
- Mitogen-activated protein kinase
- Protein kinase C
- Signal transduction
ASJC Scopus subject areas
- Physiology
- Cell Biology