Mm. Cummins et al., Purinergic responses in HT29 colonic epithelial cells are mediated by G protein alpha-subunits, CELL CALC, 27(5), 2000, pp. 247-255
Using Fura-2 to measure changes in intracellular calcium ([Ca2+](i)), we sh
ow that P-2U receptors in HT29 cells trigger an increase in [Ca2+](i) by pe
rtussis toxin-insensitive G proteins. We then use replication-deficient ade
noviruses expressing wild-type and dominant negative mutants of G(alpha q)
and G(alpha i2), antisense directed against G(alpha q) or the C-terminal fr
agment of beta-adrenergic receptor kinase (PARK-CT) to identify these G pro
teins. We find the [Ca2+](i) response to UTP is not affected by increased e
xpression of the wild-type G(alpha g), wild-type G(alpha i2) Or beta ARK-CT
, while it is blocked by over-expression of dominant negative G(alpha q). T
he timecourse of the UTP response is, however, altered by wild-type G(alpha
q) and is only weakly inhibited by antisense G(alpha q). This suggests tha
t the P-2U response is mediated, at least partially, by a G protein distinc
t from G(alpha q). In contrast, the M-3 muscarinic response is inhibited by
over-expression of antisense against G(alpha q), or over-expression of bet
a ARK-CT, a finding in agreement with our previous observation that the mus
carinic response in HT29 cells is mediated by the beta gamma-subunits of G(
q). We also find that P-2U and M-3 receptors do not control identical Ca2stores, suggesting that differential activation of G proteins can lead to C
a2+ release from distinct stores. (C) 2000 Harcourt Publishers Ltd.