Nitrergic prejunctional inhibition of purinergic neuromuscular transmission in the hamster proximal colon.
Neurogenic ATP and nitric oxide (NO) may play important roles in the physiological control of gastrointestinal motility. However, the interplay between purinergic and nitrergic neurons in mediating the inhibitory neurotransmission remains uncertain. This study investigated whether neurogenic NO modulates the purinergic transmission to circular smooth muscles of the hamster proximal colon. Electrical activity was recorded from circular muscle cells of the hamster proximal colon by using the microelectrode technique. Intramural nerve stimulation with a single pulse evoked a fast purinergic inhibitory junction potential (IJP) followed by a slow nitrergic IJP. The purinergic component of the second IJP evoked by paired stimulus pulses at pulse intervals between 1 and 3 s became smaller than that of the first IJP. This purinergic IJP depression could be observed at pulse intervals <3 s, but not at longer ones, and failed to occur in the presence of NO synthase inhibitor. Exogenous NO (0.3-1 microM), at which no hyperpolarization is produced, inhibited purinergic IJPs, without altering the nitrergic IJP and exogenously applied ATP-induced hyperpolarization. In the presence of both purinoceptor antagonist and nitric oxide synthase (NOS) inhibitor, intramural nerve stimulation with 5 pulses at 20 Hz evoked vasoactive intestinal peptide (VIP)-associated IJPs, suggesting that VIP component may be masked in the IJPs of the hamster proximal colon. Our results suggest that neurogenic NO may modulate the purinergic transmission to circular smooth muscles of the hamster proximal colon via a prejunctional mechanism. In addition, VIP may be involved in the neurotransmitter in the hamster proximal colon.
Department of Pathogenetic Veterinary Science, The United Graduate School, Gifu University, Yanagido 1-1, Japan.
Hayato
H
Matsuyama
AbuBakr
A
El-Mahmoudy
Yasutake
Y
Shimizu
Tadashi
T
Takewaki
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D003106:Colon / Q000187:drug effects / Q000294:innervation* / Q000502:physiology*; D006224:Cricetinae; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008647:Mesocricetus; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000494:pharmacology / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D052248:Nitric Oxide Synthase Type I; D010108:Oxyhemoglobins / Q000494:pharmacology; D058919:Purinergic P2 Receptor Antagonists; D011983:Receptors, Purinergic / Q000187:drug effects / Q000502:physiology*; D013498:Suramin / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D004791:Enzyme Inhibitors; D010108:Oxyhemoglobins; D058919:Purinergic P2 Receptor Antagonists; D011983:Receptors, Purinergic; D014665:Vasodilator Agents; D009569:Nitric Oxide; D014660:Vasoactive Intestinal Peptide; D013498:Suramin; D000255:Adenosine Triphosphate; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D019331:NG-Nitroarginine Methyl Ester