| Abstract |
A relationship between the membrane potential and the secretion of
glucagon was studied using a glucagon-producing tumor cell line, ITC-1,
which was established by Sugimoto et al. The membrane potential was
monitored by the potential-sensitive dye, NK-2453. Fluorescence at 505 nm
emission with excitation wave length at 460 nm was increased by changing
the potassium concentration from 5.7 to 10, 20, 40 or 60 mM, thereby
suggesting that ITC-1 cells depolarized in high-K+ Hanks solutions. An
increase in glucagon release was noticeable only when the external
potassium concentration exceeded 40 mM. In the concentration range under
20 mM, the amount of glucagon released was in the same range as that of
spontaneously released glucagon in normal Hanks solution. These results
suggest that there are two mechanisms of the glucagon secretion in ITC-1
cells. One is critically regulated by the membrane potential. The other is
responsible for the spontaneous secretion of glucagon, independently of
the membrane potential.
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