Activation of neutrophil superoxide production by concanavalin A can occur
at low levels of intracellular ionized calcium
JC Whitin, K Takahashi and HJ Cohen
The effect of concanavalin A (Con A) on the concentration of ionized
intracellular calcium [( Cai++]) in human granulocytes (PMN) was monitored
using the fluorescent calcium indicator and chelator, Quin2. The addition
of Con A to PMN resulted in a rise in [Cai++] that was markedly enhanced by
the presence of Ca++ in the external buffer. The onset of the increment in
[Cai++] preceded the onset of O2- production. The rise in [Cai++] induced
by Con A is not transient, with a new, higher steady-state level of [Cai++]
being attained within five minutes. The addition of alpha-methylmannoside
(alpha-MM) one minute after Con A resulted in the return of [Cai++] to the
original baseline level and the cessation of O2- production. The addition
of a second stimulus (such as arachidonic acid) to these cells resulted in
a second increment in [Cai++] and the return of O2- production. Thus the
rise in [Cai++] induced by Con A is tightly coupled to the activation,
inactivation, and reactivation of the O2- generating system by Con A.
Further experiments were undertaken to assess the possible requirement for
the rise in [Cai++] in the activation of PMN by Con A. PMN could be
depleted of Cai++ by loading with Quin2 in the absence of extracellular
Ca++. These Ca++- depleted PMN can be induced to produce O2- after
treatment with PMA but not with Con A. The addition of Ca++ to Ca++ -
depleted PMN results in a return of [Cai++] to the normal resting level of
Ca++ -replete PMN. The time required to return to baseline is a function of
the concentration of intracellular Quin2. The addition of Ca++ to Ca++
-depleted, Con A-treated PMN results in the elevation of [Cai++] and the
production of O2-. Over a tenfold range of intracellular Quin2
concentration, the onset of O2- production always occurred at [Cai++] that
were less than the normal resting level. Thus, activation of the O2-
generating system by Con A can occur at [Cai++] which are much lower than
the incremental level induced by Con A in Ca++ -replete PMN. Supporting
this is the observation that only a very small increment in [Cai++] is
induced by Con A in PMN cytoplasts, even though Con A could induce O2-
production in the Quin2-loaded cytoplasts.(ABSTRACT TRUNCATED AT 400 WORDS)
Volume 69,
Issue 3,
pp. 762-768,
03/01/1987
Copyright © 1987 by The American Society of Hematology
