In mammalian cells the earliest cellular responses to epidermal growth
factor (EGF) have been extensively characterized and include a number
of ionic changes, such as a transient increase in calcium influx and
a membrane hyperpolarization. The physiological significance of these
ionic changes is uncertain. Therefore it is important to establish whe
ther such ionic changes have been conserved during evolution, as this
would point to an indispensable role for ionic signaling in growth fac
tor action. We have isolated several embryonic zebrafish cell lines an
d studied the ionic events elicited by application of EGF to these cel
ls. Using whole cell patch clamp recording, we show that activation of
these receptors induces an outward current, which is dependent on the
influx of extracellular calcium, The EGF-induced transmembrane curren
ts were abolished by preincubation with different inhibitors of leukot
riene synthesis, a feature of EGF-provoked ionic signaling which is al
so observed in mammalian cell lines, Therefore, these results demonstr
ate that ionic signaling, as well as the underlying second-messenger s
ystems, is not restricted to mammalian cells, indicating that ionic si
gnaling is of importance in growth factor action. (C) 1995 Academic Pr
ess, Inc.