Background. lye have previously reported that high extracellar calcium
([Ca2+]o) levels elicited rapid increases in the cytosolic free calci
um ([Ca2+]i) and insullin release from human insulinoma cells. In this
study further investigated the mechanism for stimulus-secretion coupl
ing of insulinoma cells exposed to high levels of [Cn(2+)]o. Methods.
Insulinoma tissues were surgically obtained for primary culture. The c
hanges of [Ca2+]i level in response to various agents were monitored b
y fluoromety. Total RNA was extracted from tissues and subjected to re
verse transcription-polymerase chain reaction (RT-PCR) with calcium-se
nsing-receptor (CaR)-specific primers. PCR products were subcloned and
sequenced. Results. When [Ca2+]o level was elevated [Ca2+]i in insuli
noma cells was immediately increased. Application of neomycin abolishe
d the increase In [Ca2+]i level, although extracellular nifedipine and
lanthanum chloride did not affect it. The depletion of intracellular
calcium stoves with thapsigargin or carbachol eliminated the increase
in [Ca2+]i level. RT-PCR analysis identified the 682 bp product, of wh
ich the sequence was identical to the corresponding regions of human p
arathyroid CaR. Conclusions. Intracellular Ca2+ release might be impor
tant in insulin release from insulinoma cells after exposing to high l
evel of [Ca2+]o. CaR could be involved in this mechanism.