Evidence that tachykinins are the main NANC excitatory neurotransmitters in the guinea‐pig common bile duct

Abstract

1 Application of electrical ®eld stimulation (EFS; trains of 10 Hz, 0.25 ms pulse width, supramaximal voltage for 60 s) to the guinea-pig isolated common bile duct pretreated with atropine (1 mM), produced a slowly-developing contraction (`on' response) followed by a quick phasic`o ' contraction (`o peak' response) and a tonic response (`o late' response), averaging 16+2, 73+3 and 20+4% of the maximal contraction to KCl (80 mM), n=20 each, respectively. Tetrodotoxin (1 mM; 15 min before) abolished the overall response to EFS (n=8). 2 Neither in vitro capsaicin pretreatment (10 mM for 15 min), nor guanethidine (3 mM, 60 min before) aected the excitatory response to EFS (n=5 each), showing that neither primary sensory neurons, nor sympathetic nerves were involved. N o -nitro-L-arginine (L-NOARG, 100 mM, 60 min before) or naloxone (10 mM, 30 min before) signi®cantly enhanced the`on' response (294+56 and 205+25% increase, respectively; n=6 ± 8, P50.01) to EFS. The combined administration of L-NOARG and naloxone produced additive enhancing eects (655+90% increase of the`on' component, n=6, P50.05). 3 The tachykinin NK 2 receptor-selective antagonist MEN 11420 (1 mM) almost abolished both the`on' and`o late' responses (P50.01; n=5 each) to EFS, and reduced the`o-peak' contraction by 55+8% (n=5, P50.01). The subsequent administration of the tachykinin NK 1 receptor-selective antagonist GR 82334 (1 mM) and of the tachykinin NK 3 receptor-selective antagonist SR 142801 (30 nM), in the presence of MEN 11420 (1 mM), did not produce any further inhibition of the response to EFS (P40.05; n=5 each). At 3 mM, GR 82334 signi®cantly reduced (by 68+9%, P50.05, n=6) the`on' response to EFS. 4 The contractile`o peak' response to EFS observed in the presence of both MEN 11420 and GR 82334 (3 mM each) was abolished (P50.01; n=6) by the administration of the P 2 purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 30 mM). PPADS (30 mM) selectively blocked (75+9 and 50+7% inhibition, n=4 each) the contractile responses produced by 100 and 300 mM ATP. 5 Tachykinin-containing nerve ®bres were detected by using immunohistochemical techniques in all parts of the bile duct, being distributed to the muscle layer and lamina propria of mucosa. In the terminal part of the duct (ampulla) some labelled ganglion cells were observed. 6 In conclusion, this study shows that in the guinea-pig terminal biliary tract tachykinins, released from intrinsic neuronal elements, are the main NANC excitatory neurotransmitters, which act by stimulating tachykinin NK 2 (and possibly NK 1 ) receptors. ATP is also involved as excitatory neurotransmitter. Nitric oxide and opioids act as inhibitory mediators/modulators in this preparation.

Purinergic signalling in the gastrointestinal tract and related organs in health and disease

“…ATP, ADP and AMP are present in rat, pig and human bile, perhaps released by paracrine and/or autocrine activities, in sufficient concentrations to regulate biliary secretion [125]. Evidence has been presented to suggest that tachykinins and ATP may be excitatory cotransmitters in NANC nerves supplying the guinea pig common bile duct [543]. ATP is released into the bile by both hepatocytes and cholangiocytes, where it functions as a potent paracrine/autocrine stimulator for cholangiocyte secretion (Fig.…”

Peripheral Nervous System

“…On the basis that both the NOS inhibitor N G -nitro-L-arginine (L-NNA or L-NOARG) and PPADS produce partial inhibition of NANC relaxing responses, NO and ATP have been proposed to co-mediate the NANC response in the guinea pig taenia coli (Barthó et al 1998). Other groups support the view that NO is partially or wholly responsible for NANC inhibitory transmission in both guinea pig (Shuttleworth et al 1991(Shuttleworth et al , 1999Caballero Alomar et al 1999) and human (Tam and Hillier 1992).…”

“…ATP appears to be released together with tachykinins from intrinsic neurons in the gallbladder and bile duct, although little is known about their roles, apart from contracting smooth muscle (Patacchini et al 1998). Cl -secretion, measured by both electrophysiological and radio-nucleotide methods, is stimulated though the activation of P2Y 2 receptors in rat bile duct epithelial cells (Fitz et al 1993).…”

Exogenous Adenosine Triphosphate and Adenosine Stimulate Proximal Sphincter of Oddi Motility Via Neural Mechanisms in the Anesthetized Australian Possum

“…There are only a few reports concerning the effects of purines on SO motility and these are inconsistent. Exogenous application of adenosine triphosphate (ATP) in vitro induced a relaxation in rabbit SO [10], inhibited spontaneous activity in cat SO [11], induced a noncholinergic contractile response in guinea pig SO [12], or had no effect in human SO [13]. Further electrophysiological investigations found desensitization of P2X receptors suppressed the nonadrenergic, noncholinergic (NANC) inhibitory junction potential, suggesting ATP was a transmitter involved in the NANC relaxation of rabbit SO [14].…”