The Journal of Cell Biology, Vol 72, 456-469, Copyright © 1977 by The Rockefeller University Press
Mitogen-stimulated glucose transport in thymocytes. Possible role of Ca++ and antagonism by adenosine 3':5'-monophosphate
RR Whitesell, RA Johnson, HL Tarpley and DM Regen
The plant lectin, concanavalin A (Con-A), and the ionophore, A-23187
(specific for divalent cations), stimulated glucose transport in rat
thymocytes. Con-A stimulation developed more slowly and was somewhat less
extensive than that of stimulation developed more slowly and was somewhat
less extensive than that of A-23187. Both responses showed saturation dose
dependencies. The two responses were poorly additive, suggesting that
A-23187 may saturate regulatory processes shared by the two stimulatory
mechanisms. Doses of methylisobutylxanthine (MIX) and prostaglandin E2
which raised adenosine 3':5'-monophosphate (cAMP) levels in these cells
also antagonized the Con-A stimulation of glucose transport but did not
inhibit basal glucose transport or the A-23187 stimulation. Dibutyryl-cAMP
and 8-bromo-cAMP also natagonized Con-A stimulation without inhibiting
basal glucose transport. MIX antagonized high Con-A doses about as strongly
as it did low Con-A doses, suggesting that MIX did not compete in the Con-A
binding step or other process saturable by Con-A. [3H-A1Con-A binding was
not affected by MIX. The stimulatory effects of Con-A and A-23187 were
reduced by reduction of Ca++ in the medium. Both Con-A and A-23187 enhanced
45Ca++ influx and cellular Ca++ content. The A-23187 dose, which was
saturating for glucose transport stimulation, enhanced Ca++ influx and
cellular Ca++ content more than did the Con-A dose which was saturating for
glucose transport stimulation. The dose fo MIX which specifically
antagonized Con-A stimulation of glucose transport proved also to reduce
Ca++ influx and cellular Ca++ in the presence of Con-A but not in the
presence of A-23187. Thus, glucose transport correlates rather well with
cellular Ca++. These results are compatible with the view that Ca++ in a
cellular compartment can promote glucose transport, the Con-A's enhancement
of Ca++ entry contributes to its stimulation of glucose transport, and the
MIX antagonized Con-A action at least partly by reducing Ca++ entry. The
action of MIX is apparently mediated by cAMP.
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