Single-cell microfluorimetry techniques have been used to examine the
effects of acetylcholine (0.1-100 mu M) on the intracellular free calc
ium ion concentration ([Ca2+](i)) in a human-derived pancreatic somato
statin-secreting cell line, QGP-1N. When applied to the bath solution,
acetylcholine was found to evoke a marked and rapid increase in [Ca2](i) at all concentrations tested. These responses were either sustain
ed, or associated with the generation of complex patterns of [Ca2+](i)
transients. Overall, the pattern of response was concentration relate
d. In general, 0.1-10 mu M acetylcholine initiated a series of repetit
ive oscillations in cytoplasmic Ca2+, whilst at higher concentrations
the responses consisted of a rapid rise in [Ca2+](i) followed by a sma
ller more sustained increase. Without external Ca2+ 100 mu M acetylcho
line caused only a transient rise in [Ca2+](i), whereas lower concentr
ations of the agonist were able to initiate, but not maintain, [Ca2+](
i) oscillations. Acetylcholine-evoked Ca2+ signals were abolished by a
tropine (1-10 mu M), verapamil (100 mu M) and caffeine (20 mM). Nifedi
pine failed to have any significant effect upon agonist-evoked increas
es in [Ca2+](i), whilst 50 mM KCl, used to depolarise the cell membran
e, only elicited a transient increase in [Ca2+](i). Ryanodine (50-500
nM) and caffeine (1-20 mM) did not increase basal Ca2+ levels, but the
Ca2+-ATPase inhibitors 2,5-di(tertbutyl)-hydroquinone (TBQ) and thaps
igargin both elevated [Ca2+](i) levels. These data demonstrate for the
first time cytosolic Ca2+ signals in single isolated somatostatin-sec
reting cells of the pancreas. We have demonstrated that acetylcholine
will evoke both Ca2+ influx and Ca2+ mobilisation, and we have partial
ly addressed the subcellular mechanism responsible for these events.