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in
synovial fibroblasts
1 Department of Orthopaedic Surgery and 3 Section of Rheumatology, Department of Medicine, Louisiana State University Medical Center, Shreveport, Louisiana 71130-3932; and 2 Institute of Cell Biophysics, Russian Academy of Sciences, Pushchino 142292, Russia
The possibility that membrane depolarization of synovial
fibroblasts caused by interleukin-1
(IL-1
) was mediated by
protein kinase C (PKC) and Ca2+
influx was studied using inhibitor and activator analysis. The effect
of IL-1
was blocked by bisindolylmaleimide I, an inhibitor of PKC,
and by the Ca2+ channel blockers
nifedipine and verapamil. In other experiments, PKC was activated using
phorbol 12-myristate 13-acetate, and
Ca2+ influx was increased by means
of a Ca2+ ionophore. Simultaneous
application of phorbol ester and
Ca2+ ionophore in the absence of
IL-1
mimicked the depolarization caused by IL-1
. The results were
consistent with the hypothesis that, under the conditions studied,
activation of PKC and Ca2+ influx
are necessary and sufficient processes in the transduction of IL-1
by synovial cells leading to membrane depolarization. The
essential role of protein phosphorylation and
Ca2+ influx in the early
electrophysiological response of synovial fibroblasts to IL-1
was
therefore established. The role of IL-1
-induced depolarization in
regulating protein expression by the cells remains to be determined,
but the results reported here, taken together with observations that
protein phosphorylation and Ca2+
influx also mediate the effect of IL-1
on protease production (1, 2), suggest that electrophysiological changes are actually part of the
pathway for expression of proteases in response to IL-1
.
membrane potential; nystatin; voltage clamp
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