Journal
AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY
Volume 294, Issue 6, Pages G1376-G1383Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpgi.00078.2008
Keywords
fast synaptic transmission; enteric nervous system; electrophysiology; renzapride; single nicotinic acetylcholine receptor channels
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Funding
- NIDDK NIH HHS [R56 DK057039, R01 DK057039-04, R01 DK057039, NIH-DK57039] Funding Source: Medline
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5-HT4 receptor agonists facilitate synaptic transmission in the enteric nervous system, and these drugs are used to treat constipation. In the present study, we investigated the effects of the 5-HT4 receptor agonist, renzapride, on rundown and recovery of fast excitatory postsynaptic potentials (fEPSPs) during and after trains of stimulation and on transmitter release from individual myenteric neuronal varicosities. Intracellular electro-physiological methods were used to record fEPSPs from neurons in longitudinal muscle myenteric plexus preparations of guinea pig ileum in vitro. During trains of supramaximal electrical stimulation (10 Hz, 2 s), fEPSP amplitude declined (time constant = 0.6 +/- 0.1 s) from 17 +/- 2 mV to 0.7 +/- 0.3 mV. Renzapride (0.1 mu M) did not change the time constant for fEPSP rundown, but it decreased the time constant for recovery of fEPSP amplitude after the stimulus train from 7 +/- 2 s to 1.6 +/- 0.2 s (P < 0.05). 5-HT (0.1 mu M) also increased fEPSPs and facilitated recovery from rundown. The adenylate cyclase activator, forskolin (1 mu M), mimicked the actions of renzapride and 5-HT, whereas H-89, a protein kinase A (PKA) inhibitor, blocked the effects of renzapride. We used nicotinic acetylcholine receptor containing outside-out patches obtained from myenteric neurons maintained in primary culture to detect acetylcholine release from single varicosities. Renzapride (0.1 mu M) increased release probability twofold. We conclude that 5-HT4 receptors activate the adenylyl cyclase-PKA pathway to increase acetylcholine release from single varicosities and to accelerate recovery from synaptic rundown. These responses may contribute to the prokinetic actions of 5-HT4 receptor agonists.
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