Ionic events induced by epidermal growth factor. Evidence that hyperpolarization and stimulated cation influx play a role in the stimulation of cell growth.
Charybdotoxin, a blocker of K+ channels, and the imidazole drug SC38249, a blocker of both voltage- and second messenger-operated Ca2+ channels, were employed in mouse NIH-3T3 fibroblasts overexpressing the epidermal growth factor (EGF) receptor 1) to characterize the ionic events activated by EGF; and 2) to establish the role of those events in cell growth. The [Ca2+]i response by EGF was little changed by charybdotoxin while the parallel hyperpolarization was inhibited in a dose-dependent manner. At high toxin concentrations (greater than 3 x 10(-8) M), the effect of EGF on membrane potential was turned into a persistent depolarization sustained by both Na+ and Ca2+. Pretreatment with 10 microM SC38249 induced only minor changes of the intracellular Ca2+ release by EGF (the process responsible for the initial phase of the [Ca2+]i and membrane potential responses) and blocked the persistent, second phase [Ca2+]i and the hyperpolarization responses, both dependent on Ca2+ influx, as well as the depolarization in the charybdotoxin-pretreated cells. Long term (up to 2-day) treatment with either charybdotoxin or SC38249 failed to affect the viability and growth of unstimulated EGFR-T17 cells. Moreover, in these cells, the ionic responses to EGF were restored after a 30-min incubation in fresh medium. In contrast, growth stimulated by EGF was inhibited, moderately (-20%) by charybdotoxin and markedly (-60%) by SC38249. These results indicate for the first time that both hyperpolarization and, especially, the persistent increase of [Ca2+]i sustained by Ca2+ influx play a role in the activity of EGF, ultimately cooperating with other intracellular events in mitogenesis.
Magni
M
M
Department of Pharmacology, Scientific Institute S. Raffaele, University of Milano, Italy.
Meldolesi
J
J
Pandiella
A
A
D000818:Animals; D001692:Biological Transport; D015220:Calcium Channels / Q000187:drug effects; D002412:Cations; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D018999:Charybdotoxin; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D007477:Ions; D008564:Membrane Potentials / Q000187:drug effects*; D051379:Mice; D012604:Scorpion Venoms / Q000494:pharmacology
D015220:Calcium Channels; D002412:Cations; D007093:Imidazoles; D007477:Ions; D012604:Scorpion Venoms; D018999:Charybdotoxin; D004815:Epidermal Growth Factor; C053318:1-(2,3-bis((4-methoxyphenyl)methoxy)propyl)-1H-imidazole