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.

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.

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.

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.

[The myogenic basis of smooth muscle motility (author's transl)]. / Die myogene Basis der glattmuskulären Motorik.

Many mammalian smooth muscle tissues are able to produce spontaneous, myogenic activity. Five types of phasic-rhythmic activity can be distinguished: 1) Spikes: brief depolarizations of the membrane which trigger calcium release and contraction; 2) oscillations of the membrane potential of the second-rhythm type (SR) generating the spikes; 3) various organ-specific rhythms such as gastric and ureteral peristalsis which can be grouped together as basic organ-specific rhythms (BOR); 4) slower fluctuations of the minute-rhythm type (MR); 5) an hour-rhythm (HR) as the slowest type. In addition, some tissues generate tonic activity by special processes which can operate without spike discharges of the cell membrane. A selective blockade of phasic and tonic components is possible with some members of the group of so-called calcium antagonists. This indicates that two different calcium activation systems exist in the membrane of smooth muscle cells (P- and T-systems). Selective P- and T-blockade offers new possibilities for pharmacological influences on the smooth muscle system.

Activation of gastro-intestinal smooth muscle induced by the calcium ionophore A23187.

Tension development was recorded in isolated smooth muscle preparations from the guinea-pig, namely circular strips from the fundus and antrum region of the stomach, and taenia coli. The calcium ionophore A23187 (2-10(-6)-2-10(-5) mol/1) induced maximum activity in fundus and taenia coli, and in antrum an activity slightly smaller than that obtained with acetylcholine (ACh) (5-10(-6) mol/1). The ionophore-induced activity could be suppressed by so-called calcium antagonists: D600 (3-10(-6) mol/1) suppressed the ionophore-induced activity of taenia coli completely; phasic and tonic components in the stomach preparations were selectively suppressed by D600 and sodium nitroprusside (10(-6) mol/1), respectively.

Differentiation of the action potential in the smooth muscle of canine gastric antrum using calcium-inhibitory drugs.

Electrical and mechanical activity were recorded simultaneously in smooth muscle preparations from the antrum region of canine stomach by means of a single sucrose gap technique (SGT). The SGT was optimized to permit stable recording from multicellular smooth muscle preparations over several hours of electrical and mechanical activity with little disturbance of their normal properties. Acetylcholine (ACh, 10(-8) to 10(-6) M) induced or augmented dose-dependently the electrical and mechanical activity. The plateau of the action potential complex was elevated by ACh, while the contraction was increased in linear correlation to the magnitude of the plateau component. In spontaneously active (or in ACh-stimulated) preparations TEA (5 to 20 mM) magnified the plateau component, induced or strengthened spikes on the plateau ('secondary spikes'), and induced or strengthened phasic contractions. Nifedipine (10(-6) M) abolished secondary spikes, part of the plateau component of the action potential, and suppressed mechanical activity. The complex action potential of canine gastric antrum can be differentiated into (a) a basic action potential, consisting of an initial, primary spike and a plateau depolarization; this basic action potential is resistant to nifedipine and does not trigger any mechanical activity; and (b) a nifedipine-sensitive component (calcium component), which consists of an augmentation of the plateau depolarization and of secondary spikes, and which is responsible for the initiation of mechanical activity.

Oxygen consumption by the isolated smooth muscle of guinea-pig taenia coli.

1. An apparatus is described for simultaneous measurement of oxygen consumption and electrical and mechanical activity of isolated smooth muscle preparations.2. The mean oxygen uptake by the isolated taenia coli of the guinea-pig was 10-20 mul./g/min.3. In spontaneously active preparations, adrenaline (10(-8)-10(-7) g/ml.) caused, with the inhibition of electrical and mechanical activity, a reduction in oxygen uptake.4. After prolonged exposure to substrate free solution spontaneous activity ceased periodically. Adrenaline, when applied during a silent period, had no detectable effect on resting oxygen consumption, while readmission of substrate, either glucose or beta-hydroxybutyrate, increased oxygen uptake.5. Adrenaline did not modify the increased oxygen uptake during the initial recovery period when it was given simultaneously with the substrate. However, adrenaline shortened the time interval which elapsed from the addition of substrate until spontaneous activity was resumed, indicating an acceleration of the recovery process.

Contractile responses of canine gastric muscle to peptides of the cholecystokinin group.

1 Mechanical activity was recorded in isolated muscle preparations from the circular and longitudinal layers of different regions of canine stomach (16 dogs). At least eight muscle strips were excised from each stomach: longitudinal (lo) and circular (ci) strips from fundus (Fu), corpus (Co) and antrum (An), and circular strips from the inner and outer portion of the pyloric ring. 2 Cholecystokinin 33 (CCK 33), cholecystokinin octapeptide (CCK 8), caerulein and pentagastrin produced the same pattern of responses, with differences in their potencies: caerulein was 10 times more potent than CCK 8, and CCK eight to ten times more potent than CCK 33 and pentagastrin. 3 The most characteristic effect of the CCK peptides was an increase in frequency of the phasic activity of Fu-ci, Co and An preparations (threshold 10(-10) mol/l for CCK 8), usually combined with weak or moderate increases of amplitude. 4 Slight tonic activations were observed in Fu-lo, Co-lo and An-lo (around 10% of the ACH maximum), and stronger tonic activations in Fu-ci and Co-ci (around 50% of the ACH maximum). 5 No responses to CCK were seen in pyrolic preparations. 6 Experiments with receptor antagonists (adrenoceptors, muscarinic and histamine receptors), and with tetrodotoxin indicate that the peptides act by a direct effect on smooth muscle.

Changes of diameter and length in cylindrical segments of canine femoral arteries during activation at different pressures.

Changes in diameter and length of cylindrical segments of canine femoral arteries were recorded at different transmural pressures, and these dimensional changes have been compared with those of rings and longitudinal strips of the vessel wall. The segments responded to stimulation (noradrenaline or 40 mmol/l of potassium) with a reduction of the diameter at all transmural pressures applied. The length of the segments increased during stimulation when the transmural pressure was zero, but decreased at higher transmural pressures (60-70 mm Hg). This shortening at normal transmural pressure was converted to a small lengthening when the segment was stretched to in situ length. The factors determining these responses are discussed.

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.

Differentiation of calcium activation mechanisms in vascular smooth muscle by selective suppression with verapamil and D 600-1.

Mechanical activity of the isolated portal vein and thoracic aorta of the guinea-pig was recorded and the effects of verapamil and D 600 (methoxy-verapamil) on the dose-response curves to noradrenaline were measured. Extracellular electrical activity in portal vein was also sometimes recorded. Two calcium activation mechanisms could be differentiated: a "spike activation mechanism" (SAM) inhibited by verapamil and D 600, and a "spike-free activation mechanism" (SFAM) resistant to these antagonists in their specific concentration range (up to 10-minus 5 mol/1). In portal vein, both mechanisms were similarly dependent on extracellular calcium, indicating a D 600-resistant system for transmembrane calcium fluxes. The response of portal vein to increased potassium concentration was also tested. Species differences and differences in the specificity of various calcium antagonistic drugs complicate the picture of calcium antagonism in vascular smooth muscle.

Spike-free activation mechanism in smooth muscle of guinea pig stomach.

Electrical and mechanical activity of circular muscle strips of guinea-pigs stomach, taken from the distal corpus/proximal antrum region, were recorded. Spontaneous activity consisting of phasic contractions combined with bursts of spike potentials was suppressed by verapamil (5-10-6 - 2-10-5 mol/l). Under these conditions acetylcholine produced a spike-free tonic activation. Under normal conditions phasic contractions were superimposed on this tonic activation. The acetylcholine-induced activation, therefore, consists of two different components, one of which can be selectively blocked with verapamil. Both components disappear quickly in calcium-free solution. It can be concluded that two different calcium activation systems are responsible for the two components of activation. In comparative studies with taenia coli preparations a comparable spike-free tonic activation was not found.

Contractile responses of longitudinal and circular smooth muscle of the canine stomach to prostaglandins E and F2alpha.

Muscle strips were excised from the circular and longitudinal layers of the fundus, corpus and antrum, and from the inner portion of the pyloric ring. In general prostaglandin (PG)F2 alpha as well a PGE1 and PGE2 stimulated the longitudinal muscle. However, there were remarkable regional differences. The sensitivity to PGs was greatest in the fundus and corpus (threshold near 10(-10) mol/l) and only weak in antrum (threshold 5.10(-8) to 10(-7) mol/l). In longitudinal antrum strips acetylcholine induced a combined phasic-tonic response, whereas PGs produced purely phasic response. The effects of PGF2alpha and PGE on the circular layer were complex. PGF2 alpha produced excitatory responses in circular fundus and corpus similar to those in the longitudinal layer of the same regions. PGE produced dual responses in circular fundus (excitation at low concentration and strong inhibition at concentration of 10(-7) mol/l). In circular corpus PGE induced pure inhibition (threshold near 10(-9) mol/l for inner pylorus). These effects of PGs appeared in the presence of adrenergic and cholinergic blocking agent as well as of tetrodotoxin and were, therefore, direct effects on smooth muscle. Indomethacin (10(-7)-10(-6) mol/l) suppressed spontaneous tone of the fundus and corpus and increased phasic activity of inner pylorus. This indicates that endogenous PG synthesis may be involved in the control of spontaneous activity in gastric muscle.

A tonic component in the motility of the upper urinary tract (renal pelvis-ureter).

In isolated muscle strips of porcine renal pelvis and ureter, the calcium antagonist nifedipine (3.10(-7) moles/l) completely suppressed spontaneous phasic mechanical activity and the phasic components of an adrenaline-induced activation (P-component). In the presence of nifedipine, adrenaline induced in pelvis preparations (but not in the ureter) a tonic contraction (T-component) which was on average 61% of the control reaction (SD +/- 26%; n = 35).