Epidermal growth factor-stimulated calcium ion transients in individual A431 cells: initiation kinetics and ligand concentration dependence.
The A431 epidermoid carcinoma cell line responds to epidermal growth factor (EGF) stimulation with a number of rapid changes, including alterations in free cytosolic calcium ion concentration ([Ca2+]i). At the single cell level, these changes in [Ca2+]i are known to proceed after a clear lag phase subsequent to EGF stimulus (Gonzalez et al., 1988). The present study explores the dependence on EGF concentration of this early [Ca2+]i signal. High levels of EGF (9.0-4.3 nM) produce a [Ca2+]i spike followed by an elevation of [Ca2+]i above basal levels. The time of initiation of the spike varies from 5 to 9 s at the high dose and from 8 to 32 s at the low dose in cells that respond. A lower level of EGF (1.5 nM) produces [Ca2+]i oscillations with no prolonged elevation over basal [Ca2+]i. The initiation of response at this [EGF] ranges from 20 to 410 s. Intermediate stimulus levels generate [Ca2+]i responses that are kinetic admixtures of these limiting responses. A simple model based on the enzymatically amplified signal cascade from ligand binding through Ca2+ release or influx is examined. The model predicts a prolonged lag phase followed by a rapid increase in the [CA2+]i signal that compares favorably with the data reported here.
Cheyette
T E
TE
Department of Biochemistry, University of Massachusetts, Amherst 01003.
Gross
D J
DJ
D002118:Calcium / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000008:administration & dosage / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism
D004815:Epidermal Growth Factor; D015544:Inositol 1,4,5-Trisphosphate; D066246:ErbB Receptors; D010738:Type C Phospholipases; D002118:Calcium