Gq-linked NK(2) receptors mediate neurally induced contraction of human sigmoid circular smooth muscle.
OBJECTIVE
Because tachykinins have been identified as neurotransmitters in the guinea pig colon and human ileum, we examined a possible role of tachykinin receptors and neurokinin (NK) A in neurally induced contraction of human sigmoid colon circular muscle.


METHODS
Muscle strips were stimulated electrically for 10 seconds. Single cells were isolated by enzymatic digestion and permeabilized by saponin. [(35)S]GTPgammaS binding was assayed with or without NKA for 5 minutes. Intracellular Ca(2+) was measured using Fura 2.


RESULTS
In the presence of 100 micromol/L L-NNA, 100 micromol/L atropine did not affect electrical field stimulation (EFS)-induced contraction. A peptide NK(2)-receptor antagonist (NK-2ra) but not an NK(1) antagonist FK888 (1 micromol/L) eliminated EFS-induced contraction. NKA-induced contraction in muscle strips and single cells was virtually abolished by NK-2ra, but not by FK888. In permeabilized cells, contraction was blocked by Gq-protein antibodies, but not by other G-protein antibodies, suggesting that NKA activates Gq, which was confirmed by a [(35)S]GTPgammaS binding assay. NKA-induced contraction and increase in cytosolic Ca(2+) were abolished by depletion of intracellular Ca(2+) stores.


CONCLUSIONS
Tachykinins may be the main excitatory neurotransmitters in human sigmoid circular muscle. NKA activates Gq-linked NK(2) receptors, which cause Ca(2+) release, followed by contraction.
Cao
W
W
Department of Medicine, Rhode Island Hospital, and Brown University School of Medicine, Providence, Rhode Island, USA.
Pricolo
V E
VE
Zhang
L
L
Behar
J
J
Biancani
P
P
Kirber
M T
MT
D000368:Aged; D000369:Aged, 80 and over; D002118:Calcium / Q000502:physiology; D003106:Colon / Q000166:cytology / Q000294:innervation / Q000502:physiology*; D004151:Dipeptides / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005769:Gastrointestinal Motility / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009130:Muscle, Smooth / Q000294:innervation / Q000502:physiology*; D009424:Nervous System Physiological Phenomena; D015288:Neurokinin A / Q000494:pharmacology; D018041:Receptors, Neurokinin-2 / Q000819:agonists / Q000378:metabolism*
D004151:Dipeptides; D007211:Indoles; D018041:Receptors, Neurokinin-2; C078949:FK 888; D015288:Neurokinin A; D019204:GTP-Binding Proteins; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D002118:Calcium