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. 1988 Jan;93(1):110–120. doi: 10.1111/j.1476-5381.1988.tb11411.x

A comparison of fast and slow depolarizations evoked by 5-HT in guinea-pig coeliac ganglion cells in vitro.

D I Wallis 1, N J Dun 1
PMCID: PMC1853768  PMID: 3349227

Abstract

1. 5-Hydroxytryptamine (5-HT) was applied by pressure ejection to coeliac ganglion cells of the guinea-pig maintained in vitro and responses measured intracellularly. 2. Cells responded in one of three ways to 5-HT: by (a) a fast, transient depolarization (43%), (b) a fast transient followed by a slow depolarization (biphasic response, 30%) or (c) a slow sustained depolarization (25%). 3. Fast depolarizations (response (a) above] were graded according to the duration of the ejection pulse. Maximal responses had a mean amplitude of 12 +/- 0.8 mV, a duration of 6.4 +/- 1.0 s, a latency of 0.4 +/- 0.1 s, were associated with a fall in membrane input resistance, increased in amplitude by hyperpolarization and probably mediated by an increased conductance to Na and K. The estimated reversal potential was -22.8 +/- 2.4 mV (n = 14). The maximal fast response seen in biphasically-responding cells (b) appeared similar to fast response (a). 4. Fast depolarizations (a) showed marked tachyphylaxis and were abolished by superfusion of the ganglion with 5-HT (100 microM). They were reduced in amplitude by tubocurarine (10-100 microM, pIC50 4.4), MDL 72222 (1-5 microM, pIC50 5.8), quipazine (1 microM reduced responses by 65 +/- 15%, n = 3), ICS 205-930 (1 microM reduced responses by 64 +/- 14%, n = 7) and metoclopramide (10 microM reduced responses by about 45%), but were unafected by methysergide (up to 1 microM) or hexamethonium (up to 1 mM). 5. Slow depolarizations (c) varied in amplitude with the duration of the ejection pulse. Maximal responses had a mean amplitude of 6.4 +/- 0.7 mV, a duration of 62 +/- 6 s, a latency of 3.5 +/- 0.8 s and were reduced in amplitude by methysergide (0.1-1 microM, pIC50 6.5) but not by MDL 72222 (1 microM). The maximal slow component in biphasically-responding cells (b) was similar in amplitude and duration to slow response (c), was partially blocked by methysergide (1-5 microM) in 4 of 6 cells and was enhanced by tubocurarine (50 microM) which reduced the fast component. 6. Slow depolarizations (b,c) were associated with either a small reduction or no change in membrane input resistance depending on the cell studied. Hyperpolarization had variable effects on slow depolarization amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)

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Selected References

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