Action of FMRFamide-like peptides on porcine gastrointestinal motility in vitro.

Mechanical activity was recorded in circular and longitudinal smooth muscle preparations isolated from extensive regions of the porcine gastrointestinal tract in response to the FMRFamide-like neuropeptides F8Famide and A18Famide. In all preparations, the peptides were about equipotent in producing phasic contractions or enhancing spontaneous activity. The most prominent responses were observed in jejunal longitudinal strips which were on the average 91% (+/- 4% SEM, n = 15; 10(-6) M) of the histamine (10(-5) M) responses. The peptide-induced phasic activity was completely abolished by nifedipine but was unaffected by tetrodotoxin, atropine, phentolamine, yohimbine, phenoxybenzamine, propranolol, methysergide, cimetidine, indomethacin, levallorphane or naloxone. Both peptides enhanced acetylcholine-induced contractions. However, bovine ileum and guinea-pig taenia coli was not affected by these peptides. The results indicate that F8F- and A18F-amide contract porcine gastrointestinal smooth muscle by acting directly via non-opioid receptors on L-type calcium channels. In addition an increase of the sensitivity to cholinergic stimulation occurs.

Effects of gastrin-releasing peptide (GRP) on the mechanical activity of the human ileocaecal region in vitro.

Mechanical activity was recorded in muscle preparations isolated from the human ileocaecal region. Gastrin-releasing peptide (GRP, 10(-9)-10(-7) mol L-1) produced two types of response in the different muscle layers. Longitudinally cut strips showed a concentration-dependent increase in the rhythmic activity, whereas the circularly orientated layers generally reacted with a small decrease in tone. These effects could not be influenced by blockade of adrenergic or cholinergic receptors or nerve blockade with tetrodotoxin (TTX). Application of pentagastrin did not mimic the action of GRP. These findings suggest a direct action of GRP on smooth muscle via distinct receptors which have already been demonstrated to exist in human gastrointestinal tract. The opposite effects on circular and longitudinal strips might indicate a modulatory role of GRP in the control of ileocolonic transit.

Electrical and chemical control of smooth muscle activity of rabbit corpus cavernosum in vitro.

OBJECTIVES: This study sought to further elucidate the regulation of cavernous smooth muscle tone and to characterize mechanisms of cavernous activation and relaxation. METHODS: In isolated strips of rabbit corpus cavernosum, extracellular electrical and mechanical activity were recorded simultaneously before and after pharmacologic stimulation. RESULTS: Spontaneous mechanical activity was characterized by fast phasic contractions (frequency 6 to 30 min-1) associated with fluctuations of the extracellular electrical signals. Phasic activity was increased by blockade of potassium channels or by moderate activation of L-type calcium channels. Faster spikelike fluctuations occurred in the electrical activity, indicating the existence of spike discharges. All mechanical and electrical fluctuations were completely abolished by blockade of L-type calcium channels with nifedipine. CONCLUSIONS: Our results indicate that cavernous smooth muscle tone is regulated by both phasic and tonic activation mechanisms caused by the opening of L-type calcium channels and calcium influx through chemically controlled calcium influx/release.

Inhibitory effects of cicletanine on smooth muscle in comparison to those of nifedipine and sodium nitroprusside.

The inhibitory effect of cicletanine was studied, in comparison to the effects of nifedipine and sodium nitroprusside (SNP), in various types of smooth muscle: portal vein and iliac artery of rabbit; gastric fundus and antrum of rabbit and guinea pig; guinea pig taenia coli and uterus. In all types of tissue the nifedipine-sensitive component (LCA, L-type calcium channel dependent activation) was inhibited by cicletanine (threshold concentration 10(-6) mol/l to 10(-5) mol/l). The nifedipine to resistant component (NLCA) was in some tissues preferentially inhibited by SNP (gastric fundus) and in other tissues preferentially by cicletanine (portal vein), with graded intermediate forms (iliac artery). Consequently, the inhibitory effect of cicletanine on NLCA is different in mechanism to that of SNP. Only papaverine suppressed all types of activation.

Comparison of the relaxing effects of cicletanine and cromakalim on vascular smooth muscle.

Cicletanine inhibited the spontaneous activity of portal vein preparations (rat, guinea pig, and rabbit) and that produced by norepinephrine or an increase in external K+ concentration to 20 mmol/L in seven types of vascular smooth muscle preparation (portal vein of rat, guinea pig, and rabbit; aorta of rat and guinea pig; and iliac artery and ear artery of rabbit). The cicletanine EC50 was approximately 10(-4) mol/L. Contractions produced by K+ = 80 mmol/L were also inhibited by cicletanine in most preparations. Only in aortic strips of rat and guinea pig and in rabbit iliac artery were the concentration-response relationships for cicletanine shifted to the right, yielding EC50 values of approximately 3 x 10(-4) mol/L. In contrast, the inhibitory effects of the potassium channel opener cromakalim (BRL 34915) were completely abolished during K+ = 80 mmol/L treatment in all preparations. The inhibitory effect of cromakalim under the other test conditions (above) was completely antagonized by application of glibenclamide, 10(-5) mol/L, whereas this treatment had only negligible effects on cicletanine inhibition in most preparations. The results indicate that a potassium channel opening effect does not contribute significantly to the inhibitory effect of cicletanine on vascular smooth muscle.

Bombesin--the most stimulating peptide of human gastric smooth muscle.

The mechanical activity of isolated muscle strips from different regions of 33 human stomachs was measured under auxotonic conditions. After application of bombesin (stepwise increases in organ bath concentrations 10(-9) to 10(-6) mol/l) the following in vitro effects were observed in human gastric muscle: (1) Bombesin stimulated both circular and longitudinal preparations from all regions of the human stomach and circular duodenum. (2) The quality of the responses to bombesin application was dependent on the general myogenic characteristics of the preparations of the different stomach regions. The contraction pattern changed at high bombesin concentrations in the organ bath to slower fluctuations. (3) Bombesin resulted in a maximal tonic response in the pyloric region preparations. An increase in tone was usually observed in the inner pyloric preparations, being typical for the region. (4) The effects of bombesin on the human stomach were stronger than the effects of many other regulatory peptides and of the reaction to acetylcholine. (5) The bombesin-induced effects were unaltered by pretreatment with atropine or TTX. (6) The response to bombesin frequently lasted for hours after washing before reassuming the original state.

Myogenic basis of motility in the pyloric region of human and canine stomachs.

In vitro gastric motility was investigated in 48 human and 16 canine stomachs by measuring the mechanical activity of isolated muscle strips under auxotonic conditions. For a precise regional differentiation, we recorded the mechanical activity of longitudinal and circular strips from fundus, corpus and antrum, as well as from circular preparations of the inner and outer layer of the pyloric sphincter and from the duodenum. The analysis showed that the anatomical division of the stomach into three distinct regions resulted physiologically in different patterns of contraction in vitro for each region. The fundus exhibited purely tonic spontaneous activity and a tonic contraction pattern after application of acetylcholine whereas the activity in the circular antrum was purely phasic. A combination of tonic and phasic contractions was found in the corpus and longitudinal antrum. A major difference in the basic spontaneous activity pattern was evident between man and dog. A gradient of intrinsic frequency in the stomach from proximal to distal was seen in the dog but not in man. A physiologically distinct area exists in the pyloric region of both species adjacent to the antrum and duodenum. The pyloric ring has its own spontaneous activity (minute-rhythm), reacts to the application of acetylcholine with relatively weak contractions and, unique to the dog, was delineated by histamine-induced maximal contractions. The results provide evidence that the pyloric ring is a distinct organ with specific functional characteristics in its cellular-myogenic structure.

Phasic and tonic contraction processes in the gastrointestinal tract.

The contraction mechanisms of GI smooth muscle can be differentiated with the aid of blockers of the voltage-controlled calcium channel (e.g. nifedipine). On the one hand, nifedipine-sensitive processes produce predominantly phasic-rhythmical contractions which can merge to sustained tonic activation, called 'tetanic tone', and which are combined with spike discharges and calcium influx. On the other hand, nifedipine-resistant and electrically silent processes produce a 'specific tone'. The cooperation of both processes in one and the same cell leads to a great diversity of patterns of smooth muscle activity. 'Specific tone' dominates in regions with reservoir function and contributes significantly to the contractions of GI sphincters, with great differences between sphincter types, the various species, and, in man, also between individuals.

Contractile action of gastrin-releasing peptide on isolated preparations of human gastroduodenal muscle.

Mechanical activity was recorded in muscle preparations isolated from different regions of the human stomach (circular and longitudinal strips from fundus, corpus and antrum) and duodenum. Application of gastrin-releasing peptide (GRP, 10(-9) to 10(-7) mol/l) caused a concentration-dependent increase in the activity in all stomach strips, the height and the pattern of contraction was similar to the acetylcholine (ACh) responses (10(-7) to 10(-5) mol/l). Longitudinally cut duodenal strips were also excitable by GRP. Circularly cut duodenal strips, however, showed no responses to GRP. Both layers were excitable by ACh. The most prominent effect of GRP on longitudinal duodenal strips near the jejunum was a tonically appearing activation, which could reach up to 180% of the maximum ACh-induced activation.

Features of a calcium independent, caffeine sensitive outward current in single smooth muscle cells from guinea pig protal vein.

Using the single electrode voltage-clamp technique, vascular smooth muscle cells from the guinea pig portal vein showed an initial inward (Ca2+) current followed by an outward current which peaked within 100 ms and then declined to a steady level in a few seconds. Caffeine (1 mmol/l) selectively blocked the transient component of the outward current (ITO) and allowed differentiation of the outward current into two components: ITO and a caffeine resistant background current. The potassium channel blockers TEA (10 mmol/l) and 4-AP (5 mmol/l) produced about 90% suppression of ITO. ITO was identified as a calcium independent potassium current. Analysis of the inactivation and recovery from inactivation of ITO revealed similarities to the A-current first described for molluscan neurones (11) and later for crista terminalis of rabbit heart (4). Being much slower than this current it also bears similarities in its inactivation kinetics to a transient outward current identified in rabbit portal vein (2, 6).

Direct effects of motilin on isolated smooth muscle from various regions of the human stomach.

The effects of motilin on gastrointestinal muscles show great variations in different organs and different species. For a precise regional differentiation, we recorded the mechanical activity of longitudinal and circular strips from fundus, corpus and antrum and of circular preparations from the inner and outer layer of the pyloric sphincter and from the duodenum (20 human stomachs). Motilin produced excitatory effects on the mechanical activity of the circular muscle strips from all regions of the human stomach including the pylorus. The effects on longitudinal preparations and on duodenal strips were weak. The most striking effect was an increase of phasic activity (amplitude) in circular antrum preparations, which exceeded the acetylcholine- and bombesin-induced activity. In pylorus preparations, a strong stimulation of phasic activity was observed with a transition to tonic activity in the inner layer of the pyloric ring at high motilin concentrations. The motilin-induced activity of the pyloric preparations was greater than the acetylcholine-induced contractions and even exceeded the bombesin-induced responses in the outer pylorus. The responses of the muscle strips of the proximal stomach (fundus and corpus) were weaker and did not exceed the acetylcholine-induced activity. All effects remained unaltered by atropine and tetrodotoxin application. The study confirms that motilin can interact directly with the smooth muscle of human stomach.

Angiotensin II stimulates human gastric smooth muscle in vitro.

1. For a precise analysis of angiotensin II (ANG) effects on human gastric muscle, we dissected longitudinal (lo) and circular (ci) strips from fundus (Fu), corpus (Co) and antrum (An), and circular muscle from the inner and outer part of the pyloric sphincter (Py-inn and Py-out) and from duodenum. The mechanical activity of these muscle strips was recorded simultaneously under auxotonic conditions. Preparations were taken from a total of 10 stomachs (from organ donors or gastrectomy preparations). 2. Excitatory effect after application of ANG (10(-9) to 10(-6) mol l-1) were regularly observed in all types of preparation (threshold: 10(-9) mol/l). 3. The quality of the responses depended on the general characteristics of the type of preparation. Tonic types of muscle showed predominantly tonic responses to ANG (Fu-lo, Fu-ci, Co-lo). Purely phasic muscles (An-ci) showed increases of the phasic activity (amplitude up to 33% delta 1). Intermediate types of muscle exhibited combined phasic/tonic responses (Co-ci, An-lo). Phasic responses were also seen in Py-out. Inner pyloric muscle (Py-inn) responded only to a small extent to ANG. Phasic/tonic activations were observed in the duodenal preparations, accompanied by slight increases in frequency. 4. The intensity of the ANG-induced responses often exceeded the maximum acetylcholine-induced activation. The qualitative pattern of ANG responses was similar to that of bombesin-induced activation.

Direct effects of cholecystokinin on human gastric motility.

For a precise analysis of the cholecystokinin (CCK 8) effects on human stomach, we dissected strips of longitudinal and circular muscle from the fundus, corpus and antrum, and circular muscle from the inner and outer pyloric sphincter and duodenum. Specimens were taken during gastrectomy and from stomachs of kidney donors. Mechanical activity was simultaneously recorded under auxotonic conditions. After CCK 8 application, the following effects were observed: (1) direct excitatory effects of CCK 8 with great regional variations in quality and intensity; (2) increases in amplitude of phasic contractions in the outer plyorus and longitudinal antrum (in the other types of preparations the effects were negligible; (3) increases in tonic activity in preparations of the proximal stomach and in strips of longitudinal muscle form the antrum, and (4) remarkable interindividual differences, with negligible responses in one third of the 24 human stomachs examined.

Tonic contraction of canine gastric muscle during long-lasting calcium removal and its dependence on magnesium.

1. Tonic contractions induced by acetylcholine (ACh) in canine gastric fundus preparations were shown to persist during long-lasting exposure to Ca2+-free solution containing EGTA (1 mmol/l). These EGTA-resistant contractions amounted to up to more than 50% of maximal ACh-control responses in physiological salt solution. They could be evoked repeatedly for more than 20 h without reduction in size, each contraction lasting as long as ACh was present. 2. During prolonged exposure to Ca2+-free solution at normal Mg2+ concentration ([Mg2+]O = 1.2 mmol/l), the preparations exhibited a slowly developing contracture (elevation of the baseline of contraction), which was particularly pronounced in strips taken from the circular layer of the muscular wall (44% of control ACh-maximum after 4 h in Ca2+-free solution). Contracture could be suppressed either by increasing [Mg2+]O to 6-10 mmol/l or by depolarizing the cell membrane (replacement of external Na+ by K+). However, contracture also developed if, at physiological [Na+]O and [K+]O, [Mg2+]O was further increased to 50 mmol/l. 3. The combined effects of [Mg2+]O and membrane potential suggest that contracture is caused by a gain of Mg2+ by the cells. This conclusion is based on the assumption that (a) the cytoplasmic Mg2+ concentration is determined by the transmembrane electrochemical gradient acting on Mg2+, the magnesium permeability of the cell membrane (PMg) and an active extrusion mechanism, and that (b) Ca2+ removal leads to an increase of PMg which is (partly) prevented by an appropriate increase of [Mg2+]O. 4. 45Ca efflux experiments, performed at [Mg2+]O = 10 mmol/l to avoid interference of ACh responses with contracture, showed that the cellular 45Ca content decreased from some 200 mumol/kg wet wt. to less than 10 mumol/kg wet wt. within 10-20 h in Ca2+-free solution. Activations by ACh did not produce any detectable increase in 45Ca efflux. 5. The calcium ionophore A23187 (10(-5) mol/l), applied in order to increase the calcium permeability of the cell membrane, did not reduce the EGTA-resistant contractions. 6. Experimental procedures conducted to replace calcium within intracellular stores by strontium or barium did not affect the EGTA-resistant ACh response. However, prior uptake of manganese by the cells had an amplifying effect. 7. Caffeine (30 mmol/l) failed to produce contraction in Ca2+-free solution, whereas ACh evoked contractile responses, both in the presence of and after application of caffeine.(ABSTRACT TRUNCATED AT 400 WORDS)