Guinea Pig Gallbladder Muscle Research Articles

C-Kit expression in the gallbladder of guinea pig with chronic calculous cholecystitis and the effect of Artemisia capillaris Thunb on interstitial cells of Cajal.

To study the c-Kit expression in the gallbladder of cholesterol lithogenic guinea pig model and the effect of Artemisia capillaris Thunb on interstitial cells of Cajal (ICCs). A total of 45 guinea pigs were randomly assigned into three groups: the control group (guinea pigs fed a standard diet, normal group); the model group (guinea pigs fed a cholesterol gallstone-inducing diet); and the Chinese medicine group (guinea pigs fed the cholesterol gallstone-inducing diet and treated with A. capillaris through intragastric administration, therapy group). Each group had 15 guinea pigs. The gallbladders of the guinea pigs were harvested after 8 weeks. C-Kit expression was detected using an immunohistochemistry staining, real-time PCR, and Western blot analyses. The effect of A. capillaris on ICCs was evaluated by muscle strip contraction experiments. C-Kit expression significantly decreased in the gallbladder of model group, but increased in the Chinese medicine group. The Contractility of guinea pig gallbladder muscle strip significantly improved in the Chinese medicine group. Our results indicated that A. capillaris improves gallbladder impairment by up-regulating c-Kit expression, and it also can improve the contractile response of in vitro guinea pig gallbladder muscle strips.

High levels of caveolar cholesterol inhibit progesterone-induced genomic actions in human and guinea pig gallbladder muscle.

Gallbladder disease is prevalent during pregnancy. It has been suggested that this complication of pregnancy is attributable to increased bile cholesterol (Ch) induced by estrogens and to gallbladder hypomotility caused by increasing levels of progesterone (P4). Studies on nonpregnant gallbladders have shown that increased levels of bile Ch contribute to both gallstone formation and bile stasis. These studies investigated the effects of high levels of plasma membrane Ch on P4 on gallbladder muscle cells from human and guinea pigs. Contraction was studied in intact and permeabilized muscle cells. G proteins were determined by Western blot, and 3H-P4 incorporation by muscle cells was measured in the beta-scintillation counter. High levels of caveolar Ch blocked the effects induced by P4 treatment for 6 h. They suppressed the expected P4 inhibition of GTP-gammaS (a G protein activator)-induced contraction and changes in G proteins by downregulating Gi3 and upregulating Gs protein levels. Ch inhibited these P4 actions at the caveolar 3 (CAV-3) level, since the P4 effects were antagonized by treatment with CAV-3 antibody, by reducing CAV-3 expression through CAV-3 siRNA. CAV-3 antibody and siRNA reduced caveolar Ch levels. High caveolar levels of Ch and CAV-3 antibody blocked the incorporation of 3H-P4 into caveolae. Treatment with GDP-betaS (a G protein antagonist) had no effect on P4 actions. High caveolar Ch levels blocked the P4 effects on muscle contraction and G protein changes probably because both Ch and P4 require CAV-3 proteins for their transport across the plasma membrane.

Control of gallbladder contractions by cholecystokinin through cholecystokinin-A receptors on gallbladder interstitial cells of cajal

To identify the cholecystokinin (CCK)-A receptors (CCK-AR) on the guniea pig gallbladder interstitial cells of cajal (ICC) and to study CCK-8 induced gallbladder muscle strip contractions through the CCK-AR. The existence of CCK-AR was examined by immunohistofluorescence on sectioned tissue and cultured cells. In vitro contractile response of guinea pig gallbladder muscle strips and the strips with ICC removed were also studied with CCK-8 receptors added. In tissue sections, intensely CCKAR-immunoreactive interstitial cells were found mainly in the muscular layers. In cultured cell sections, distinctive double staining of C-kit and CCK-AR ICCs were found. When we removed the ICC of the gallbladder, CCK-8 induced muscle strip contraction dose response curve significantly shifted to the right. We proved that both the existence of CCK-AR on the guinea pig gallbladder ICC and CCK evoked contraction are mediated through direct action on CCK-AR on the gallbladder ICC.

Reactive oxygen species are messengers in maintenance of human and guinea pig gallbladder tonic contraction

The tonic contraction of human and guinea pig gallbladder (GB) is dependent on basal levels of PGE(2) and thromboxane A(2) (TxA(2)). The pathway involved in the genesis of these prostaglandins has not been elucidated. We aimed to examine the source of reactive oxygen species (ROS) and whether they contribute to the genesis of GB tonic contraction by generating basal prostaglandin levels. Tonic contraction was studied in human and guinea pig GB muscle strips treated with ROS scavengers (Tiron and catalase), apocynin (an inhibitor of NADPH oxidase), and NOX-1 small interference RNA (siRNA). The subunits of NADPH oxidase and their functional roles were determined with specific antibodies in GB muscle cells. ROS scavengers reduced the GB tonic contraction and H(2)O(2) and PGE(2) levels. Apocynin also inhibited the tonic contraction. Antibodies against subunits of NADPH oxidase present in GB muscle cells lowered H(2)O(2) and PGE(2) levels. NOX-1 siRNA transfection reduced the tonic contraction, NOX-1 expression, and levels of H(2)O(2) and PGE(2). Tiron and apocynin inhibited the expected increase in tension and H(2)O(2) levels induced by stretching of muscle strips. H(2)O(2) increased the levels of PGE(2) and TxA(2) by increasing platelet-activating factor-like lipids that phosphorylate p38 and cPLA(2) sequentially. H(2)O(2) generated by NADPH oxidase participates in a signal transduction pathway that maintains the GB tonic contraction by activating PAF, p38, and cPLA(2) to generate prostaglandins.

Melatonin Treatment Reverts Age-Related Changes in Guinea Pig Gallbladder Neuromuscular Transmission and Contractility

The incidence of gallbladder illness increases with age, but the altered mechanisms leading to gallbladder dysfunction are poorly understood. Here we determine the age-related alterations in gallbladder contractility and the impact of melatonin treatment. Isometric tension changes in response to electrical field stimulation and to agonists were recorded from guinea pig gallbladder muscle strips. [Ca(2+)](i) was determined by epifluorescence microscopy in fura-2 loaded isolated gallbladder smooth muscle cells, and F-actin content was quantified by confocal microscopy. Aging reduced neurogenic contractions, which was associated with the impairment of nitrergic innervation and with increased responsiveness of capsaicin-sensitive relaxant nerves, possibly involving calcitonin gene-related peptide. Melatonin treatment for 4 weeks restored neurogenic responses to normal values, with an associated recovery of nitrergic function and the disappearance of the capsaicin-sensitive component. Aging also reduced the contractile responses to cholecystokinin and Ca(2+) influx. The impaired contractility only correlated with diminished Ca(2+) mobilization in response to activation of Ca(2+) influx. Melatonin improved contractility and increased smooth muscle F-actin content without changing Ca(2+) homeostasis. In conclusion, aging impairs gallbladder function as the result of changes in the inhibitory neuromodulation of smooth muscle contractility and the reduction in the myogenic response to contractile agonists. Impaired contractility seems to be related to decreased Ca(2+) influx and damage of contractile proteins. Melatonin significantly ameliorated these age-related changes.

Enhancement of EFS-induced contractions, by agmatine, in guinea pig gallbladder smooth muscle strips

Electrical field stimulation of gallbladder muscle strips produces frequency-dependent contractions by activating cholinergic nerves. The cholinergic motor function of the gallbladder and enteric system is also modulated by other mediators. The aim of this study was to investigate the role of agmatine, a ligand for alpha 2-adrenoceptors and imidazoline binding sites, in the cholinergic motor activity of guinea pig gallbladder smooth muscle. Gallbladder muscle strips obtained from guinea pigs were subjected to electrical field stimulation (1-64 Hz, 100 V, 1-ms pulse width, and 10-s train duration). Frequency-response contractions of gallbladder muscle strips were traced before and after the addition of cumulative concentrations of agmatine (10(-5)-10(-3) M) to the tissue bath. The same set of experiments was repeated in the presence of different antagonists. Agmatine by itself did not produce any contractions in guinea pig gallbladder muscle strips, but significantly enhanced the contractile response produced by electrical field stimulation. Yohimbine (10(-6) M), a selective alpha 2-adrenergic blocker, neither decreased nor increased the enhancement induced by agmatine. However, idazoxan (10(-4) M), an alpha-receptor blocker and imidazoline receptor antagonist, abolished this enhanced contractile response. Pretreatment with N(W)-nitro L-arginine methyl ester (L-NAME; 30 microM), and indomethacin (10 microM) did not inhibit the effect of agmatine. Our findings indicate that agmatine has a modulator role in the electrical field stimulation-induced cholinergic contractions of guinea pig gallbladder smooth muscle strips, and this role could be mediated by imidazoline receptors. Receptor binding studies should be done to determine the presence of endogenous agmatine and imidazoline receptors in gallbladder smooth muscle.

Natriuretic peptides cause relaxation of human and guinea-pig gallbladder muscle through interaction with natriuretic peptide receptor-B

Atrial natriuretic peptide (ANP) binding sites have been demonstrated in the guinea-pig gallbladder muscle with unclear function. To investigate effects of natriuretic peptides in the gallbladder, we measured relaxation of isolated human and guinea-pig gallbladder strips caused by natriuretic peptides, including C-type natriuretic peptide (CNP), brain natriuretic peptide (BNP) and ANP, as well as des[Gln 18, Ser 19, Gly 20, Leu 21, Gly 22]ANP(4-23) amide (cANP(4-23)), a selective natriuretic peptide receptor-C (NPR-C) agonist. Results in the human gallbladder were similar to those in the guinea-pig gallbladder. CNP, BNP, ANP and cANP(4-23) alone did not cause contraction or relaxation in resting gallbladder strips. However, in carbachol or endothelin-1-contracted strips, CNP caused moderate, sustained and concentration-dependent relaxation. The relaxation was not affected by tetrodotoxin or atropine in endothelin-1-contracted gallbladder strips and not by tetrodotoxin in carbachol-contracted strips. These indicate a direct effect of CNP on the gallbladder muscle. The relative potencies for natriuretic peptides to cause relaxation were CNP>>BNP≥ANP. cANP(4-23) did not cause relaxation. These indicate the existence of the natriuretic peptide receptor-B (NPR-B) mediating the relaxation. Taken together, these results demonstrate that natriuretic peptides cause relaxation of human and guinea-pig gallbladder muscle through interaction with the natriuretic peptide receptor-B.

Relaxant effect of omeprazole and lansoprazole in guinea pig gallbladder muscle strips in vitro.

The aim of this study was to investigate the role of omeprazole and lansoprazole, H(+)-K(+) ATPase inhibitors, in gallbladder smooth muscle contractility in vitro. Gallbladder muscle strips obtained from guinea pigs were mounted in an organ bath. The responses of both precontracted strips and strips under basal tension to omeprazole and lansoprazole were determined. Spontaneous contractile activity was blocked following omeprazole and lansoprazole administration. The agents also caused concentration-dependent relaxation in carbachol- and KCl-precontracted gallbladder muscle strips. Pretreatment with atropine (1 microM), N(W)-nitro L-arginine methyl ester (L-NAME; 30 microM), indomethacin (10 microM), ammonium chloride (7.5 mM), sodium acetate (7.5 mM), tetraethylammonium chloride (0.5 mM), glibenclamide (1 micro M), 4-aminopyridine (0.1 mM), or clotrimazole did not inhibit this relaxation. Gallbladder strips were placed in high-concentrtion potassium (80 mM), calcium-free solution. The contraction produced with the addition of Ca(2+) (2.5 mM) was completely relaxed by omeprazole, lansoprazole, and nifedipine separately. These results demonstrate that omeprazole and lansoprazole have potent inhibitory effects on spontaneous contractions and cause dose-dependent relaxation in precontracted gallbladder smooth muscle strips of guinea pig in vitro. This effect could be due to blockade of the calcium channels.

Investigation of the mechanism of nicotine-induced relaxation in guinea pig gallbladder

Background. Muscular contraction of the gallbladder is the primary determinant of bile delivery into duedonum. Gallbladder filling and emptying are influenced by both inhibitory and excitatory stimuli, and NO plays a key role in normal relaxation. In this study, to determine whether nicotine acts on the gallbladder muscle, the mechanism of its effect on strips of guinea pig gallbladder was studied in vitro. Materials and methods. Guinea pig gallbladder muscle strips were mounted in organ bath with modified Krebs-Henseleit solution and aerated with Carbogen. Tension was measured with isometric force transducers, and muscle relaxation was expressed as percent decrease of precontraction induced by carbachol. Results. Nicotine produced concentration dependent relaxation when preparations were precontracted by carbachol (10 −6 M). Nicotine-induced relaxation was 51.6 ± 3.2% of phenylephrine contraction and was not affected by guanethidine (10 −5 M), propranolol (10 −6 M), hexamethonium (10 −4 M), indomethacin (10 −5 M), N w-nitro l-arginine methyl ester ( l-NAME) (3 × 10 −5 M), methylene blue (10 −5 M), glibenclamide (10 −5 M), clotrimazole (10 −6 M), tetraethylammonium (3 × 10 −4 M), or 4-aminopyridine (10 −3 M). Nicotine did not exhibit a calcium antagonizing effect. Conclusions. From these results, we concluded that nicotine-induced relaxation of the guinea pig gallbladder is not mediated by the release of noradrenaline, nitric oxide (NO), prostaglandins, or a related substance, or by the activation of potassium channels, or by the stimulation of nicotinic cholinoceptors. Further work is needed to determine the cellular mechanism(s) of action by which nicotine acts on gallbladder smooth muscle.

Contribution of different phospholipases and arachidonic acid metabolites in the response of gallbladder smooth muscle to cholecystokinin

Guinea pig gallbladder muscle strips were used to investigate the contribution of different sources of diacylglicerol (DAG) in the cholecystokinin (CCK)-induced contraction. The involvement of arachidonic acid (AA) in this response was also investigated. Three distinct pathways for DAG production were investigated with specific phospholipase (PL) inhibitors. U-73122 (10 μM) was used for inhibition of phosphoinositide-specific-PLC (PI-PLC), D-609 (100 μM) for phosphatidylcholine specific-PLC (PC-PLC), and propranolol (100 μM) for phospholipase D (PLD). Separate or combined inhibition of each of these enzymes showed that the CCK-induced output of DAG involves the parallel activation of each of these phospholipases. Thus, after inhibition of a PL subtype, the remaining subtypes were able to functionally compensate in mediating CCK-induced contraction. Inhibition of AA production via DAG-lipase or phospholipase A 2 (PLA 2) was accomplished using RHC-80267 (40 μM), mepacrine (100 μM) and 4-BPB (100 μM). These inhibitors diminished contractile response, indicating that AA is an important modulator of CCK-induced contraction. Indomethacin (10 μM) and nordihydroguaiaretic acid (NDGA, 100 μM), which inhibit subsequent steps in AA metabolism through the cyclooxygenase and 5-lipooxygenase pathways, also inhibited contractions. Taken together, these results show that CCK redundantly activates PC-PLC, PI-PLC and PLD, to produce DAG, which in turn stimulates PKC and provides a substrate for the generation of AA. sPLA 2 is also a source of AA, whose metabolites are, in part, responsible for determining the magnitude of the CCK-evoked contraction.

Endothelin-1 induces contraction of human and Australian possum gallbladder in vitro

Background: Endothelin-1 (ET-1) stimulates guinea pig gallbladder (GB) muscle strip contractility; however, the role and source of ET-1 in the GB remains to be elucidated. Aims: To determine the effect of ET-1 on human and possum GB muscle strip contractility and evaluate whether ET-1 is present in GB tissue. Methods: GB muscle strips were mounted in organ baths to measure isometric tension. ET-1 was added cumulatively with and without pretreatment with the neural blocker tetrodotoxin (TTX) or the ET receptor antagonists BQ-123, BQ-788, and tezosentan. Immunohistochemical localization of ET was performed on freshly fixed and cultured GBs. Results: ET-1 induced concentration-dependent increases in tone in human and possum GB strips ( p<0.05). This response was unaffected by BQ-123, BQ-788, and TTX but antagonized by BQ-123+BQ-788 in the human tissue only. Tezosentan (10 −4 mol/l) blocked the ET-1-induced response in human and possum GB strips ( p<0.001). Although ET immunoreactivity was absent in freshly fixed possum GB, immunoreactivity was observed in the GB epithelium of freshly fixed human tissue and in both possum and human tissue following 24 h of organ culture. Conclusion: ET-1 acts directly on human and possum GB smooth muscle producing contractions, possibly via ET-B receptors. ET may be present under pathophysiological conditions altering GB function.

Endothelin receptors in human and guinea-pig gallbladder muscle

We measured contraction of muscle strips caused by endothelin (ET) isopeptides and binding of 125I-ET-1 to muscle cell membranes prepared from human and guinea-pig gallbladders. Visualization of 125I-ET-1 binding sites in tissue was performed by autoradiography. Results in human were similar to those in guinea-pig. ET-1 caused tetrodotoxin and atropine-insensitive contraction. The relative potencies for ET isopeptides to cause contraction were ET-1=ET-2>ET-3. ET-1 caused contraction was only slightly inhibited by BQ-123 (potent ET A receptor antagonist) and not by BQ-788 (potent ET B receptor antagonist). It was inhibited by the combination of both. Autoradiography localized 125I-ET-1 binding to the smooth muscle layer. Binding of 125I-ET-1 to muscle cell membranes was saturable and specific. Analysis of dose–inhibition curves demonstrated the presence of two classes of receptors. One class (ET A receptor) had a high affinity for ET-1 and ET-2 but a low affinity for ET-3, and the other (ET B receptor) a high affinity for ET-1, ET-2 and ET-3. These results demonstrate that similar to guinea-pig, human gallbladder possesses both ET A and ET B receptors cooperating to mediate muscle contraction.

Myosin light chain phosphorylation correlates with contractile force in guinea pig gallbladder muscle.

Acetylcholine (ACh)-induced gallbladder smooth muscle contraction involves myosin light chain phosphorylation (MLCP). ACh-induced contraction is dose dependent. Whether MLCP by ACh is also dose dependent and how it correlates with contractile force have not been carefully evaluated. This study investigated the correlation between gallbladder muscle contraction and MLCP. Guinea pig gallbladder muscle strips were studied isometrically and frozen after different doses of ACh (0, 0.1, 5, 100 microM) for different periods of incubation (0.5, 1, 2, 3, 4 min). MLCP was determined using gel electrophoresis. Both contraction and MLCP in response to ACh were concentration dependent. Peak MLCP to ACh 100 microM occurred at 30 sec. There was a high correlation between active force and MLCP (r = 0.991; P = 0.009 at 30 sec stimulation). Nifedipine 1 microM reduced ACh-induced contraction and MLCP by a similar degree (31% and 33%, respectively). In conclusion, gallbladder contractile force significantly correlates with MLCP. This is consistent with the hypothesis that initiation of gallbladder cholinergic contraction is dependent on phosphorylation of myosin light chains.

Effects and mechanisms of action of taurochenodeoxycholic acid on guinea pig gallbladder muscle

Effects and mechanisms of action of taurochenodeoxycholic acid on guinea pig gallbladder muscle

Subtypes of muscarinic receptors regulating gallbladder cholinergic contractions.

The aim of this study was to determine the functional role of muscarinic receptor subtypes regulating gallbladder cholinergic contractions. Electrical field stimulation (EFS; 16 Hz) produced contractile responses of guinea pig gallbladder muscle strips in vitro that were inhibited by 1 microM tetrodotoxin (2 +/- 2% of control) and 1 microM atropine (1 +/- 1% of control), indicating activation of intrinsic cholinergic nerves. Exogenous ACh (5 microM)-induced contractions were inhibited by atropine (1 +/- 1% of control) but not tetrodotoxin (102 +/- 1% of control), indicating a direct effect on smooth muscle. The M1 receptor antagonist pirenzepine (10 nM) had no effect on ACh-induced contractions but inhibited EFS-induced contractions by 11 +/- 3%. The M2 antagonist methoctramine (10 nM) had no effect on ACh-induced contractions but augmented EFS-induced contractions by 5 +/- 2%. The M3 antagonist 4-DAMP (10 nM) inhibited ACh-induced contractions by 14 +/- 4% and EFS-induced contractions by 22 +/- 5%. In conclusion, specific M1, M2, and M3 receptors modulate gallbladder muscle contractions by regulating ACh release from cholinergic nerves and mediating the contraction. Cholinergic contractions are mediated by M3 receptors directly on the smooth muscle. M2 receptors are on cholinergic nerves and function as prejunctional inhibitory autoreceptors. M1 receptors are on cholinergic nerves and function as prejunctional facilitatory autoreceptors.

Investigation of endogenous neurotransmitters of guinea pig gallbladder using nicotinic agonist stimulation.

Gallbladder motility is modulated by intrinsic nerves, the identities of which are not well established. The aim of this study was to determine the effect of nicotinic receptor stimulation of intrinsic nerves on gallbladder muscle contractility. Guinea pig gallbladder muscle strips were studied in vitro. Histamine 1 microM was used to increase baseline tone. The nicotinic receptor agonist, 1,1-dimethyl-4-phenylpiperazinium (DMPP), produced a biphasic response characterized by an initial transient contraction followed by a sustained relaxation. The initial contraction was inhibited by the neural blocker tetrodotoxin, the nicotinic antagonist hexamethonium, and the muscarinic antagonist atropine, but not by a substance P receptor antagonist or a bombesin receptor antagonist. The relaxation response to DMPP was not affected by tetrodotoxin, but was reduced by hexamethonium and omega-conotoxin GVIA, an inhibitor of neurotransmitter release. The relaxation response was reduced by the nitric oxide synthase inhibitor L-NAME, but not by a vasoactive intestinal peptide antagonist or propranolol. DMPP produces a biphasic response in the guinea pig gallbladder. The initial contractile response is mediated by nicotinic receptors on the cell body or axon of cholinergic nerves. The relaxation response appears to result, in part, from activation of nicotinic receptors on nerve terminals of nitric oxide-releasing nerves. These results suggest nicotinic receptors have heterogeneity in location depending on excitatory or inhibitory neuronal function.

Dual effects of PACAP on guinea pig gallbladder muscle via PACAP-preferring and VIP/PACAP-preferring receptors.

The aims of this study were to determine the effect and mechanism of action of pituitary adenylate cyclase-activating peptide (PACAP) on gallbladder muscle. Guinea pig gallbladder muscle strips were studied isometrically. In noncontracted muscle strips, PACAP-27 and PACAP-38 caused dose-dependent contractions, whereas vasoactive intestinal peptide (VIP) caused dose-dependent relaxation. PACAP-27 contractions were resistant to tetrodotoxin, atropine, and the substance P receptor antagonist [D-Arg1,D-Trp7,9,Leu11]substance P (Spantide) but were inhibited by the selective PACAP receptor antagonist PACAP-(6-38) and slightly increased with the VIP receptor antagonist [4-chloro-D-Phe6,Leu17]VIP. In cholecystokinin-precontracted muscle strips, both VIP and PACAP caused relaxations. This relaxant effect of PACAP-27 was inhibited by PACAP-(6-38) and [4-chloro-D-Phe6,Leu17]VIP, but not by tetrodotoxin. These studies suggest that PACAP has dual excitatory and inhibitory effects on guinea pig gallbladder muscle. The contractile effect of PACAP is a direct action on muscle through PACAP-preferring receptors. The relaxant effect of PACAP is seen in precontracted muscle strips and mediated through VIP/ PACAP-preferring receptors.

Effect of modulating voltage-dependent calcium channels on cholecystokinin and acetylcholine-induced contractions of the guinea pig gallbladder

The aim of this study was to investigate the role of extracellular Ca 2+ utilization in cholecystokinin (CCK) and acetylcholine-induced guinea pig gallbladder contractions by using agents that modulate influx of extracellular Ca 2+ through voltage-dependent calcium channels. METHODS: Guinea pig gallbladder muscle strips were studied isometrically at L max in vitro. Results: (1) Acetylcholine and CCK caused dose-dependent contractions, with ED max of 10 −4 to 10 −6 M, respectively. (2) Preventing influx of extracellular Ca 2+ by incubation in Ca 2+-free/0.1 mM EGTA solution inhibited the acetylcholine (10 −4 M)-induced contraction by 60 ± 3% compared to only 46 ± 5% ( P $ ̌ 0.05 ) for CCK (10 −6 M)-induced contraction. (3) Nifedipine (3 μM) inhibited the response to acetylcholine (10 −4 M) by 54 ± 3%, compared to only 34 ± 3% ( P < 0.01) for CCK (10 −6 M). (4) Bay K 8644 (10 −7 M) significantly increased ( P < 0.05) the contractile responses to low doses of each agonist: acetylcholine (10 −6 M) by 121 ± 44% and CCK (10 −9 M) by 94 ± 31%, but had no effect on the contraction to the ED max of each agonist. Conclusions: These studies demonstrate: (1) acetylcholine and CCK cause guinea pig gallbladder contraction by both intracellular Ca 2+ release and influx of extracellular Ca 2+ through voltage-dependent calcium channels; (2) the CCK-induced contraction is more dependent on intracellular Ca 2+ than is acetylcholine; and (3) acetylcholine and CCK-induced contractions can by modulated by manipulating influx of extracellular Ca 2+ through voltage-dependent calcium channels.

The effect of phosphatase inhibitors on myosin light chain phosphorylation and relaxation in guinea pig gallbladder and urinary bladder smooth muscle

The effect of phosphatase inhibitors on myosin light chain phosphorylation and relaxation in guinea pig gallbladder and urinary bladder smooth muscle

Pharmacological analysis of receptors for bombesin-related peptides on guinea pig gallbladder smooth muscle

The aim of this study was to characterize the receptor(s) for bombesin (BN) and its homologues (gastrin releasing peptide, GRP; neuromedin B, NMB; neuromedin C, NMC) in guinea pig gallbladder muscle strips. Dose-dependent contractions were induced by all peptides tested (potency: BN = GRP > NMC > NMB, but with similar efficacy: BN = GRP = NMC = NMB). The contractions were resistant to tetrodotoxin, atropine, phentolamine, and propranolol. BN tachyphylaxis (1 μM) abolished subsequent contractile responses to BN, GRP and NMC; and partially antagonized the response to NMB (66 ± 7% inhibition). NMB tachyphylaxis (10 μM) markedly inhibited subsequent contractile responses to NMB (78 ± 5%); and partially antagonized the contractile response to BN (36 ± 4%), GRP (31 ± 12%) and NMC (22 ± 2%). At 1 μM, both [ d-Phe 6, Des-Met 14]-BN(6–14) ethylamide and ICI 216,140, two BN receptor antagonists, reduced the contractile actions of BN (82 ± 4% and 59 ± 8% inhibition, respectively), GRP (75 ± 11% and 45 ± 5%), and NMC (73 ± 9% and 51 ± 6%) while having no marked effect on NMB contractions. Our pharmacological approaches (receptor tachyphylaxis and differential antagonism) provide support for two types of receptors for BN-like peptides on guinea pig gallbladder smooth muscle: a GRP-preferring receptor and a NMB-preferring receptor.