Purinergic and nitrergic junction potential in the human colon.
The aim of the present work is to investigate a putative junction transmission [nitric oxide (NO) and ATP] in the human colon and to characterize the electrophysiological and mechanical responses that might explain different functions from both neurotransmitters. Muscle bath and microelectrode techniques were performed on human colonic circular muscle strips. The NO donor sodium nitroprusside (10 microM), but not the P2Y receptor agonist adenosine 5'-O-2-thiodiphosphate (10 microM), was able to cause a sustained relaxation. NG-nitro-L-arginine (L-NNA) (1 mM), a NO synthase inhibitor, but not 2'-deoxy-N6-methyl adenosine 3',5'-diphosphate tetraammonium salt (MRS 2179) (10 microM), a P2Y antagonist, increased spontaneous motility. Electrical field stimulation (EFS) at 1 Hz caused fast inhibitory junction potentials (fIJPs) and a relaxation sensitive to MRS 2179 (10 microM). EFS at higher frequencies (5 Hz) showed biphasic IJP with fast hyperpolarization sensitive to MRS 2179 followed by sustained hyperpolarization sensitive to L-NNA; both drugs were needed to fully block the EFS relaxation at 2 and 5 Hz. Two consecutive single pulses induced MRS 2179-sensitive fIJPs that showed a rundown. The rundown mechanism was not dependent on the degree of hyperpolarization and was present after incubation with L-NNA (1 mM), hexamethonium (100 microM), MRS 2179 (1 microM), and NF023 (10 microM). We concluded that single pulses elicit ATP release from enteric motor neurons that cause a fIJP and a transient relaxation that is difficult to maintain over time; also, NO is released at higher frequencies causing a sustained hyperpolarization and relaxation. These differences might be responsible for complementary mechanisms of relaxation being phasic (ATP) and tonic (NO).
Gallego
Diana
D
Department of Cell Biology, Physiology and Immunology, Edifici V, Universitat Autònoma de Barcelona 08193, Bellaterra, Barcelona, Spain.
Gil
Víctor
V
Aleu
Jordi
J
Aulí
Mariona
M
Clavé
Pere
P
Jiménez
Marcel
M
D000200:Action Potentials; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000368:Aged; D000369:Aged, 80 and over; D012809:Colon, Sigmoid / Q000187:drug effects / Q000294:innervation*; D004558:Electric Stimulation; D017615:Enteric Nervous System / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005769:Gastrointestinal Motility / Q000187:drug effects; D006801:Humans; D008875:Middle Aged; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation*; D009433:Neural Inhibition; D009469:Neuromuscular Junction / Q000378:metabolism; D018733:Nicotinic Antagonists / Q000494:pharmacology; D026602:Nitrergic Neurons / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors
D004791:Enzyme Inhibitors; D018733:Nicotinic Antagonists; D020030:Nitric Oxide Donors; D018048:Receptors, Purinergic P2; D009569:Nitric Oxide; D000255:Adenosine Triphosphate; D019001:Nitric Oxide Synthase