Many hormones, growth factors and neurotransmitters stimulate the prod
uction of inositol 1,4,5-trisphosphate evoking the release of calcium
from intracellular stores. The depletion of these intracellular calciu
m stores subsequently activates a voltage-independent plasma membrane
calcium influx in many cell types. This store-operated calcium influx
is essential for generating prolonged cytosolic calcium signals and fo
r refilling the intracellular calcium stores. Recent studies suggest t
hat the store-operated calcium channels may be encoded by the trp fami
ly of genes, which show structural homology to voltage-operated channe
ls. Ankyrin-like repeats encoded by trp may be involved in regulating
the channel by a direct interaction with the inositol 1,4,5-trisphosph
ate receptor on the intracellular calcium stores.