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要旨

We recently showed that prostaglandin E₂ (PGE₂) causes depolarization in cells at the base of isolated crypts from rat distal colon by activating nonselective cation channels. In order to investigate whether PGE₂ acts via intracellular cyclic adenosine monophosphate (cAMP), the effect of forskolin on cell potential and on whole-cell current was investigated using the slow whole-cell patch-clamp method with nystatin. In addition, effects of forskolin in cells at other sites along the crypt were investigated. At the crypt base, the unstimulated cells had a resting potential of -70.6±1.3 mV (n=25). When forskolin was added to the bath, the cells depolarized to -21.1±1.5 mV (n=25). This depolarization was inhibited by substitution of all Na⁺ in the bath solution by N-methyl-D-glucamine (NMDG⁺) or by addition of flufenamic acid (50 mumol/l), a blocker of nonselective cation channels, to the bath. In contrast, the Cl⁻ channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, 50 mumol/l) did not affect the depolarization. Moving along the crypt, the resting potential was -66.8±1.8 mV (n=11) in the mid-crypt and -48.1±2.9 mV (n=9) in cells of the upper part of the crypt. Forskolin caused a strong depolarization to about -20 mV in all parts of the crypt. In contrast to cells at the base, this depolarization was only partly diminished by substitution of Na⁺ by NMDG⁺, whereas substitution of bath Cl⁻ by gluconate caused an initial further depolarization, followed by a repolarization to the cell's resting potential.