Sphingosine 1-phosphate stimulates na+-h+ exchange in thyroid frtl
-5 cells.
T[diaeresis]ornquist, Kid.
Department of Biosciences, Division of Animal Physiology,
University of Helsinki, and the Minerva Foundation Institute for
Medical Research, Helsinki, Finland
APStracts 3:0348C, 1996.
Sphingosine derivatives are potent mitogens in several cell types.
Many mitogens activate the Na+-H+ exchange, although the
interrelationships between Na+-H+ exchange and mitogenesis are
unclear. The present investigation in thyroid FRTL-5 cells shows that
sphingosine 1-phosphate (SPP) activates Na+-H+ exchange in a dose
dependent manner in acid-loaded cells. The effect of SPP was
abolished in a Na+-free buffer, and by pretreatment of the cells with
ethylisopropylamiloride. SPP did not affect basal pHi. SPP stimulated
the release of sequestered calcium, and a substantial entry of
calcium. The effect of SPP on pHi was abolished in cells incubated in
a calcium-free buffer, and in cells loaded with the intracellular
calcium chelator BAPTA. Furthermore, the effect of SPP was abolished
in pertussis toxin-treated cells. Pertussis toxin decreased calcium
entry only, without affecting the release from intracellular stores.
Phosphatidic acid (PA) did not activate Na+-H+ exchange, suggesting
that the effect of SPP was not mediated via activation of
phospholipase D and the production of PA. Thus, one mechanism of
action of SPP in FRTL-5 cells appears to be to activate Na+-H+
exchange. This action is mediated via a G protein-dependent
mechanism, and requires an increase in intracellular free calcium.
Received 9 July 1996; accepted in final form 2 October 996.
APS Manuscript Number C386-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996