Substance P is essential for maintaining gut muscle contractility: a novel role for coneurotransmission revealed by botulinum toxin.
Substance P (SP) is commonly coexpressed with ACh in enteric motor neurons, and, according to the classical paradigm, both these neurotransmitters excite smooth muscle via parallel pathways. We hypothesized that, in addition, SP was responsible for maintaining the muscular responsiveness to ACh. We tested this hypothesis by using botulinum toxin (BoNT/A), a known blocker of vesicular release of neurotransmitters including ACh and neuropeptides. BoNT/A was injected into rat pyloric sphincter in different doses; as control we used boiled BoNT/A. At the desired time point, pylorus was dissected out and pyloric contractility was measured ex vivo in an organ bath and by measuring phosphorylation of myosin light chain 20 (MLC20). BoNT/A (10 IU) significantly reduced the response of pyloric muscle to exogenous ACh, an effect that was accompanied by reduced MLC20 phosphorylation in the muscle. Both effects were reversed by exogenous SP. CP-96345, a NK1 receptor antagonist, blocked the ability of exogenous SP to reverse the cholinergic hyporesponsiveness as well as the reduction in MLC20 phosphorylation induced by BoNT/A. In conclusion, we have identified a novel role for SP as a coneurotransmitter that appears to be important for the maintenance of muscular responsiveness to the principal excitatory neurotransmitter, ACh. These results also provide new insight into the effects of botulinum toxin on the enteric nervous system and gastrointestinal smooth muscle.
Johns Hopkins Center for Neurogastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland;
Cuiping
C
Li
Department of Anesthesiology, University of Texas Medical Branch, Galveston, Texas; and.
Maria-Adelaide
MA
Micci
Division of Gastroenterology, Hepatology and Nutrition, Virginia Commonwealth University, Richmond, Virginia.
Karnam S
KS
Murthy
Johns Hopkins Center for Neurogastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; ppasric1@jhmi.edu.
Pankaj Jay
PJ
Pasricha
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology; D001905:Botulinum Toxins / Q000494:pharmacology*; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D018994:Myosin Light Chains / Q000378:metabolism; D011706:Pyloric Antrum / Q000187:drug effects / Q000502:physiology; D011708:Pylorus / Q000187:drug effects; D051381:Rats; D018040:Receptors, Neurokinin-1 / Q000187:drug effects; D013373:Substance P / Q000494:pharmacology / Q000502:physiology*
D001713:Biphenyl Compounds; D018994:Myosin Light Chains; D018040:Receptors, Neurokinin-1; D013373:Substance P; D001905:Botulinum Toxins; D000109:Acetylcholine; C066892:CP 96345
MLC phosphorylation; acetylcholine; botulinum toxin; cholinergic responsiveness; coneurotransmission; gut smooth muscle contractility; substance P