Biomedical subjects

E E Daniel

Publications and source records attributed to E E Daniel.

At least 217 records · Page 12Linked to original sources

PubMed1989

Effect of the novel cholecystokinin receptor antagonist CR-1392 on cholecystokinin-induced antroduodenal and pyloric motor activity in vivo.

The effects of i.a. injected cholecystokinin (CCK)-octapeptide on pyloric and antroduodenal motility, measured with strain gauges and combined side hole-sleeve manometry, were investigated in 16 dogs in vivo. CCK-octapeptide (OP) induced strong pyloric contractions when injected into the pylorus (threshold of 2 x 10(-13) mol; ED50, 8 x 10(-13) mol). Similar responses were obtained in the distal antrum (threshold, 6 x 10(-13) mol; ED50, 3 x 10(-12) mol) and the proximal duodenum (threshold, 5 x 10(-13) mol; ED50, 3 x 10(-12) mol). The nonsulfated form of CCK-OP was about 2 to 3 log units less potent in eliciting these excitatory responses in the pylorus (threshold, 9 x 10(-10) mol). Atropine shifted the dose-response curve of CCK-OP in pylorus, duodenum and antrum to the right suggesting a neural action of CCK-OP. However, an excitatory effect of CCK-OP was still present after neural blockade with tetrodotoxin i.a. Therefore, there was probably a muscular as well as a neural site of action of CCK-OP in these tissues. Systemic application of the novel CCK-antagonist CR-1392 in a dose of 1.2 mg/kg i.v. plus 100 micrograms i.a. shifted the dose-response curve of CCK-OP 1 log unit to the right without affecting the dose-response curve to acetylcholine. This dose of CR-1392 did not interfere with the pyloric motor responses to duodenal field stimulation or to intraduodenal acid infusion. These results demonstrate the dual peripheral action on nerve and muscle of CCK-OP in the pylorus in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Modulation of pyloric motor activity via adrenergic receptors.

The influences of adrenergic nerves on pyloric motor function and the locus and types of receptors involved were examined. Using glyoxylic acid fluorescence a dense adrenergic innervation of the inner pyloric muscle ring was demonstrated. Pyloric motor activity was monitored while close i.a. injections of a selective alpha-1 adrenoceptor agonist, phenylephrine, or a selective alpha-2 adrenoceptor agonist, B-HT-920, were given. Neither agonist affected basal pyloric motor activity, but both inhibited pyloric activity when it was stimulated by duodenal field stimulation or by intraduodenal acid infusion. The actions of each of the inhibitory agonists, phenylephrine or B-HT-920, were blocked selectively by prazosin or rauwolscine, respectively. Injection of isoproterenol usually had no effect or excited basal pyloric activity. This excitation could be antagonized selectively by propranolol or by atropine. Injection of isoproterenol after neural blockade by tetrodotoxin inhibited pyloric motor activity. Receptor binding studies carried out with subcellular nerve or muscle enriched membrane fractions of canine pyloric muscle with [3H]prazosin, [3H]rauwolscine and [125I]cyanopindolol revealed a dual location of alpha-1, alpha-2 and beta receptors on both nerve membranes and smooth muscle membranes. These results suggest that adrenergic effects on the pyloric muscle can be exerted by pre- and postsynaptic beta receptors which, respectively, excite by releasing acetylcholine and inhibit by acting on receptors on the pyloric muscle. Also inhibitory alpha-1 and alpha-2 receptors are present on cholinergic nerves. The functions of postsynaptic alpha-1 and alpha-2 adrenoceptor binding sites on smooth muscle are so far unknown.

Animals↗

PubMed1988

Interstitial cells of Cajal in the canine colon: a special communication network at the inner border of the circular muscle.

The ultrastructure of the region shown to be essential for pacemaking activity of the circular muscle of the canine colon was studied. This region, at the inner border of the circular muscle, consists of a network of several layers of interstitial cells of Cajal type III. These are interconnected to one another and to the adjacent circular muscle cells by numerous gap junctions. Elsewhere in circular muscle, gap junctions are rare and small. In addition, interstitial cells are in close (often less than 20 nm) contact with nerve varicosities containing large granular vesicles or sometimes small granular vesicles. The morphology of interstitial cells resembles that of others of type III. It is suggested that this arrangement of interstitial cells, circular smooth muscles, and nerves allows for a tightly coupled network of membrane oscillators to be subject to neural modulation.

Animals↗

PubMed1988

Influence of recording techniques on measurement of canine colonic motility.

The extent to which the established variability in colonic motility recordings is due to differences in recording techniques is not known. The aim of this study was to compare the ability of two intraluminal recording devices (perfused tube and tube mounted strain gauge) to record colonic motor activity against a reference device (serosal strain gauge). In six anesthetized dogs an intracolonic probe was positioned such that the component perfused tubes and tube mounted strain gauges were approximated to identical strain gauges mounted on the serosa. Contractions were induced by field stimulation and intraarterial injections of acetylcholine and carbachol. While both intraluminal devices demonstrated limitations in the detection of phasic and tonic motor events, perfused tubes detected a significantly greater proportion of tonic and phasic contractions than did strain gauges (P less than 0.001). Intraluminal strain gauges misrepresented 50% of tonic contractions (confirmed visually and by serosal strain gauges) as waveforms with negative polarity. This was not seen in recordings from perfused tubes. Perfused tubes represented tonic contractions as biphasic or bifid waveforms significantly less frequently than strain gauges (P less than 0.05). Radial asymmetry of colonic contractions is likely to account for these observed discrepancies. Recorded motility patterns are influenced by different recording techniques, and these differences are a source of variability in recorded patterns of colonic motor activity.

Acetylcholine↗

PubMed1988

Structural changes in tracheal nerves and muscle associated with in vivo sensitization of guinea pigs.

The ultrastructure of guinea-pig tracheal smooth muscle and its innervation were studied in control and antigen (ovalbumin) sensitized animals. There was a reduction in the frequency and in the proportion of membrane occupied by gap junctions in sensitized muscle. In addition, there was a decrease in the proportion of varicosities with small granular vesicles relative to other nerve varicosities and to the number of smooth muscle cells. Earlier functional studies in vitro (Mansour and Daniel, 1987) did not reveal altered function of adrenergic nerves or adrenoceptors concentration-response curves to a wide variety of agonists and showed few changes. These studies suggest that inflammatory mediators released during antigen-sensitization may regulate the density of gap junctions and influence nerve structure. These studies also suggest that procedures to evaluate directly cell-to-cell coupling and nerve function after sensitization are needed.

Animals↗

PubMed1988

Effects of inhibition of prostaglandin synthesis on uterine oxytocin receptor concentration and myometrial gap junction density in parturient rats.

The development of oxytocin (OT) sensitivity in the parturient uterus is associated with increases in myometrial OT receptor concentration, gap junction formation, and prostaglandin (PG) production. To investigate whether PGs mediate these responses, we measured OT responsiveness, OT receptor concentrations, and gap junction formations in uteri of Day 19, 20, 21, 22, 23 pregnant and Day 2 postpartum rats. Inhibition of endogenous PG synthesis was produced by infusion of naproxen sodium delivered by an implanted osmotic pump. Naproxen treatment, but not placebo treatment, markedly attenuated in vitro uterine PGE2, PGF2 alpha, and PGI2 releases, suppressed OT responsiveness, and prolonged gestation. The increase of OT receptor concentration that normally occurred on Day 23 term pregnancy was delayed to Day 24. Co-administration of PGF2 alpha reversed the suppressive effects of naproxen. Naproxen treatment did not significantly affect gap junction formations on Day 23 but appeared to delay both the onset and disappearance of gap junction formations. PGF2 alpha co-administration with naproxen also had no apparent effect on gap junction development. The inhibition of OT receptor formation but not gap junction formation on Day 23 in the presence of naproxen indicates that these two events are controlled independently. Furthermore, the failure of naproxen-treated rats to deliver at term suggests that gap junction formation in the absence of an increase in OT receptors is insufficient to initiate labor. It appears that increases in both OT receptor concentrations and gap junction densities may be required for labor.

Animals↗

PubMed1988

Extrinsic and intrinsic neural control of pyloric sphincter pressure in the dog.

1. In chloralose-urethane-anaesthetized dogs a manometric assembly was inserted via a gastrostomy to monitor pyloric pressure with a sleeve sensor. Antral and duodenal contractions were monitored with both manometric side holes and serosal strain gauges. 2. Subserosal silver wire electrodes were placed in the antrum 5 cm orad and the duodenum 3 cm aborad to the pylorus to facilitate field stimulation of intramural nerves. 3. The pylorus exerted spontaneous tone (10.8 +/- 4.8 mmHg) with phasic contractions occurring at a rate varying from 1-5 min-1 and, at times, with a superimposed higher frequency up to 15 min-1. Atropine (30 micrograms kg-1 I.V. and 10 micrograms I.A.) reduced and tetrodotoxin (50-100 micrograms I.A.) enhanced the phasic activity significantly. 4. Bilateral cervical vagal section had no consistent influence on pyloric motility. 5. Stimulation of the distal ends of the cervical vagal nerves at low frequencies (0.2-0.5 Hz, 1-3 ms, 20 V) induced phasic pyloric contractions, which were abolished by atropine or hexamethonium (10 mg kg-1 I.V. and 1 mg I.A.). Higher frequencies (greater than 0.7 Hz) of stimulation inhibited both phasic and tonic contractions and this inhibition was unaffected by atropine, hexamethonium, phentolamine (1.5 mg kg-1 I.V. and 100 micrograms I.A.) or propranolol (1 mg kg-1 I.V. and 100 micrograms I.A.). All neural responses were blocked by tetrodotoxin (50-100 micrograms I.A.). 6. Duodenal field stimulation (0.2-5 Hz, 0.5 ms, 40 V) induced strong phasic and tonic contractions in the pylorus. This excitation was blocked by atropine, hexamethonium, tetrodotoxin (50-100 micrograms I.A.) or duodenal transection orad to the stimulating electrodes. 7. Antral field stimulation (0.5-1 Hz, 0.5 ms, 40 V) completely abolished phasic activity in the pylorus and reduced tonic activity, regardless of whether the contractile activity was spontaneous or induced by neural stimulation. This inhibitory action was unaffected by atropine, hexamethonium or propranolol but was blocked by tetrodotoxin and antral transection aborad to the stimulating electrodes. Phentolamine attenuated the inhibitory effect of antral field stimulation on pyloric motility. 8. It is concluded that the distal canine pylorus exhibits myogenic tone and phasic activity which is modulated by extrinsic and intrinsic nerve pathways. Vagal nerves contain fibres, activated by different stimulus parameters which can either excite or inhibit pyloric activity. Activation of antral nerves inhibits pyloric activity, with both non-adrenergic, non-cholinergic and phentolamine-sensitive pathways contributing to this inhibitory response.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Neural control of canine colon motor function: studies in vivo.

The responses of the circular muscle of canine colon to stimulation of intrinsic nerves and to the probable mediators of these nerves were studied in vivo. In vivo studies were carried out using close intra-arterial injections and local field stimulation of proximal, mid-, and distal colon while recording circumferential contractions. Our results suggest that acetylcholine is the major excitatory mediator, but another excitatory mediator could be released by high frequency field stimulation after atropine. Norepinephrine had mixed inhibitory and excitatory effects, but no evidence was obtained that it was released by field stimulation. Substance P had mainly excitatory effects partly by a mechanism involving nerves and partly by a direct effect on muscle; it in addition to norepinephrine deserves further evaluation as the mediator of noncholinergic excitation to high frequency field stimulation. There is no explanation of the inhibition it produced after initial excitation during field stimulation. Vasoactive intestinal peptide had inhibitory effects but these were incomplete and inconsistent. This may be related to our inability to demonstrate relaxation or inhibition to field stimulation after atropine. Further evaluation of the possible role of vasoactive intestinal peptide and other agents as nonadrenergic, noncholinergic inhibitory mediators is required.

Animals↗

PubMed1988

Neural control of canine colon motor function: studies in vitro.

The responses of strips of the canine colon to stimulation of intrinsic nerves and to the probable mediators of these nerves were studied in vitro. Studies were carried out using longitudinal and circular muscle strips from proximal and distal colon with field stimulation and addition of agents to the bath. Overall, these and other studies in vivo suggested that acetylcholine was an ubiquitous mediator of neural excitation. Norepinephrine had mixed inhibitory and excitatory effects, the latter only in circular muscle. Inhibitory effects of norepinephrine seemed to be both pre- and post-synaptic but no evidence that it was released by field stimulation was obtained. Substance P had excitatory effects chiefly by release of acetylcholine. It, in addition to norepinephrine, at least in circular muscle, deserves evaluation as the mediator of noncholinergic excitation to high frequency field stimulation. Although vasoactive intestinal peptide sometimes had inhibitory effects, these were incomplete and inconsistent. However, further evaluation of its possible role as a nonadrenergic, noncholinergic inhibitory mediator is required to determine if it is involved as one component in the response. Few qualitative differences existed between responses of various regions of the colon to potential neuromediators, although there were some consistent differences between responses of longitudinal and circular muscle. Some differences existed in responses obtained earlier in vivo and in vitro. In particular, inhibitory effects following excitation by substance P on field stimulation were found only in vivo. Nonadrenergic, noncholinergic inhibitory responses to field stimulation were consistently present only in vitro. These differences have not been explained.

Animals↗

PubMed1988

The effects of EGTA on vascular smooth muscle contractility in calcium-free medium.

The effect of EGTA, commonly present in Ca2+-free physiological saline solution, on the contractile responses induced by Ca2+ and phenylephrine was studied in dog mesenteric arteries and aortas of rats and rabbits. EGTA substantially enhanced the contractile responses of these vascular strips or rings to added Ca2+ after a prolonged preincubation period in the Ca2+-free medium. The maximal level of the enhanced contractile responses was independent of EGTA concentration, but the rate of the maximal responses was faster at higher EGTA concentration, presumably as a result of faster removal of intracellular Ca2+. Such a Ca2+-induced response was sensitive to the Ca2+ antagonist, nifedipine. EGTA present at low concentrations (50 and 400 microM) in Ca2+-free medium also inhibited the phenylephrine-induced contractile response more prominently for the longer preincubation periods of the vascular tissues in Ca2+-free medium. Our results suggest that EGTA, even when added at low concentrations to the vascular smooth muscle for a sufficiently long period in Ca2+-free medium, may cause destabilization of the cell membranes leading to increased permeability to subsequently added Ca2+. EGTA may also remove the superficially bound Ca2+ and subsequently reduce the intracellular Ca2+ pool via extraction of the intracellular Ca2+ at the cell membrane surfaces.

Animals↗

PubMed1988

Electrophysiological analysis of responses to intrinsic nerves in circular muscle of opossum esophageal muscle.

The nerve-mediated responses to electrical field stimulation (EFS) along the opossum esophageal circular smooth muscle were studied with the sucrose-gap recording technique. Strips from 1-2, 4-5, 7-8, and 10-11 cm above the lower esophageal sphincter were stimulated with short-train (300 ms) and long-train (3 s) durations at 29 degrees C. The response always consisted of a hyperpolarization [inhibitory junction potentials (IJP)] followed by an "off depolarization" often associated with spike potentials and mechanical contraction. Proximal to distal differences in the characteristics of the evoked responses were found, i.e., increasing amplitude, duration and time to peak hyperpolarization of the IJP, increasing latency, and amplitude of the off depolarization. Neither atropine, scopolamine, physostigmine, nor guanethidine altered these characteristics substantially. Circular strips of muscularis externa, studied in the organ bath at 37 degrees C using 10-s EFS trains at 5-40 pps, produced off contractions, enhanced by physostigmine and reduced by atropine. High-frequency stimulation occasionally initiated small persistent intrastimulus ("on") responses; some were sensitive to cholinergic agents, but there was no gradient in the delay in their onset. Atropine-insensitive and tetrodotoxin-potentiated transient on responses were occasionally detected. We conclude that only the noncholinergic, nonadrenergic innervation provides a functional intrinsic innervation directly to the opossum esophagus circular smooth muscle when nerves are activated by EFS.

Acetylcholine↗

PubMed1988

Inhibitory opioid receptors in canine pylorus.

In 18 anesthetized dogs, antroduodenal and pyloric motility was monitored in vivo by a sleeve and perfused side-hole manometric assembly and by antral and duodenal serosal strain gauges. Close intra-arterial injection to the pylorus of dynorphin-(1-13) (Dyn) for kappa-receptors, [D-Pen2,5]enkephalin (DPen2,5-Enk) for delta-receptors, and [N-Me-Phe3-D-Pro4]morphiceptin (PL017) and [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAGO) for mu-receptors showed no excitatory effect in the pylorus. When pyloric motor activity was increased by duodenal field stimulation 3-5 cm aboaad from the pylorus, Dyn greater than DPen2,5-Enk greater than DAGO produced a dose-dependent inhibition of the pyloric motor activity. Naloxone (200 micrograms/kg iv and 20 micrograms ia) had no effect on the pyloric excitation due to duodenal field stimulation, but it reduced the inhibitory response of intra-arterially injected opioids. In addition, opioid binding ([3H]diprenorphine) in microsomal and mitochondrial fractions from the inner circular muscle ring of the pylorus showed a distribution similar to the neuronal marker [3H]saxitoxin but no correlation to the plasma membrane marker 5'-nucleotidase. These results suggest the existence of inhibitory opioid receptors (kappa- and delta-receptors) on excitatory neurons in the intestinal neuronal pathway, which activates the canine pylorus.

Animals↗

PubMed1988

Characteristics of canine lower esophageal sphincter: a new electrophysiological tool.

The canine lower esophageal sphincter (LES) was evaluated as a model for investigation of the electrophysiology of nonadrenergic noncholinergic neurotransmission. The LES contained a dense collection of gap junctions and a moderate number of nerves located at the periphery of muscle bundles, which are often associated with interstitial cells of Cajal. These cells make gap junctions with one another and with smooth muscle cells. The nerve varicosities contained many large dense cored vesicles. In vitro the LES produced spontaneous active tone and relaxed to field stimulation that was blocked by tetrodotoxin (TTX). Increase of stimulus duration or frequency produced a partially TTX-insensitive sphincter relaxation. Basal tone and nerve-mediated relaxation were unaffected by cholinergic, histaminergic, or adrenergic antagonists. Acetylcholine, carbachol, or histamine caused TTX-insensitive contractions mediated by M2- and H1-receptors, respectively. Vasoactive intestinal peptide (10(-6) M) and isoproterenol (10(-6) M) relaxed the LES to the same extent as field stimulation. In the double sucrose gap this tissue regularly produced inhibitory junction potentials when field stimulated. The canine LES has appropriate morphological and pharmacological properties for the electrophysiological study of nonadrenergic noncholinergic neural responses, their mechanisms, and mediators.

Animals↗

PubMed1988

[3H]saxitoxin as a marker for canine deep muscular plexus neurons.

The objectives of this study are 1) to examine the potential of [3H]saxitoxin binding as a marker for the neuronal membranes in canine small intestinal muscle membrane preparations, 2) to develop a synaptosomal preparation from deep muscular plexus, and 3) to partially characterize [3H]saxitoxin binding to this fraction. A purified synaptosomal fraction, relatively low in the smooth muscle plasma membrane marker enzyme 5'-nucleotidase but enriched in [3H]saxitoxin binding (2,592 fmol/mg), was obtained on sucrose density gradient. Vasoactive intestinal peptide immunoreactivity was also highest (51.82 pmol/mg protein) in this fraction. The binding was rapid at 20 degrees C with quick and complete dissociation after the addition of excess unlabeled tetrodotoxin (TTX). Scatchard analysis of the saturation binding data revealed a single population of binding sites (Bmax = 5,705 fmol/mg protein). The affinity constants calculated from the kinetic and saturation data were in close agreement (Kd = 0.26 and 0.69 nM, respectively). TTX competed for the binding (Ki = 2.1 nM), whereas veratridine and guanidinium hydrochloride did not. Monovalent and divalent cations had differential effects on the binding.

Animals↗

PubMed1988

Thromboxane effects on canine trachealis neuromuscular function.

The objective of this study is to determine which inflammatory mediators had direct effects on canine trachealis muscle neuromuscular control to identify candidate mediators of the hyperresponsiveness observed in vitro after O3 exposure. Studies were carried out in the sucrose gap at 29 degrees C and in the muscle bath at 37 degrees C. Leukotriene (LT) B4, LTD4, and prostaglandin (PG) D2 had neither direct nor significant effects on the excitatory junction potentials (EJP's), the secondary membrane potential oscillations, or the associated contractions that followed field stimulation of cholinergic nerves. U 46619, a stable analogue of thromboxane (Tx) A2, enhanced (10(-10)-10(-7) M) the duration and the amplitude of secondary oscillations and associated contractions without affecting the EJP's. In the muscle bath, U 46619 enhanced field-stimulated contractions; this was antagonized competitively by SQ 29548. In both the sucrose gap and the muscle bath, higher concentrations (10(-9) M and higher) caused direct effects, small depolarizations, and contractions. These effects of U 46619 were unaffected by indomethacin or guanethidine but were abolished by SQ 29548, an antagonist selective at TxA2-PGH2 receptors. U 46619 at 10(-9) M did not affect electrical or mechanical responses to acetylcholine and at 10(-9) M did not increase the sensitivity to acetylcholine. Platelet-activating factor (PAF) was inactive in all muscle-bath and most sucrose-gap experiments. In 7 of 20 of the latter, it caused effects qualitatively like those of U 46619, but whether it acted through release of TxA2 could not be tested because of the rapid tachyphylaxis to PAF. We conclude that TxA2 may mediate the hyperresponsiveness found in vitro after O3 treatment.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1988

Airway smooth muscle responsiveness from dogs with airway hyperresponsiveness after O3 inhalation.

Airway hyperresponsiveness occurs after inhalation of O3 in dogs. The purpose of this study was to examine the responsiveness of trachealis smooth muscle in vitro to electrical field stimulation, exogenous acetylcholine, and potassium chloride from dogs with airway hyperresponsiveness after inhaled O3 in vivo and to compare this with the responsiveness of trachealis muscle from control dogs. In addition, excitatory junction potentials were measured with the use of single and double sucrose gap techniques in both groups of dogs to determine whether inhaled O3 affects the release of acetylcholine from parasympathetic nerves in trachealis muscle. Airway hyperresponsiveness developed in all dogs after inhaled O3 (3 ppm for 30 min). The acetylcholine provocative concentration decreased from 4.11 mg/ml before O3 inhalation to 0.66 mg/ml after O3 (P less than 0.0001). The acetylcholine provocative concentration increased slightly after control inhalation of dry room air. Airway smooth muscle showed increased responses to both electrical field stimulation and exogenous acetylcholine but not to potassium chloride in preparations from dogs with airway hyperresponsiveness in vivo. The increased response to electrical field stimulation was not associated with a change in excitatory junctional potentials. These results suggest that a postjunctional alteration in trachealis muscle function occurs after inhaled O3 in dogs, which may account for airway hyperresponsiveness after O3 in vivo.

Acetylcholine↗

PubMed1988

Release of epithelium-derived relaxing factor after ozone inhalation in dogs.

Airway epithelium has been reported to release epithelium-derived relaxing factor (EpDRF), which inhibits contraction of airway smooth muscle. This study tested the hypothesis that airway hyperresponsiveness after inhalation of ozone in dogs results from an inability to produce EpDRF. Two groups of five dogs each were studied; one group inhaled ozone, the other dry room air. Ozone-treated dogs developed airway hyperresponsiveness, whereas the control group did not. The acetylcholine provocative concentration decreased from 4.17 (%SE 1.35) to 0.56 mg/ml (%SE 1.24) (P = 0.0006) in the ozone-treated dogs and was 18.76 (%SE 2.04) and 29.77 mg/ml (%SE 2.07) in the air-treated dogs (P = 0.47). In vitro the presence of airway epithelium reduced the constrictor responses to acetylcholine, histamine, serotonin, and KCl in trachealis strips from the control dogs. This effect of epithelium was still present in trachealis strips from dogs with airway hyperresponsiveness. These results demonstrate that EpDRF is released from canine tracheal epithelium, that this function is not impaired in dogs with airway hyperresponsiveness after inhaled ozone, and that loss of EpDRF is not responsible for the development of airway hyperresponsiveness after inhaled ozone in dogs.

Acetylcholine↗

PubMed1988

Morphology and contractile properties of smooth muscle cells isolated from the dog carotid artery.

Collagenase and elastase treatment was used to isolate vascular smooth muscle cells from canine carotid artery. Their structure and function were compared to those in situ. Morphological studies showed that these cells when relaxed in situ were 120-133 micron mean length, connected by numerous typical gap junctions, covered by a basal lamina and like other smooth muscles in structure. After isolation, the median length of single cells was 82 micron. There was structural evidence of some contraction and the basal lamina was absent, but many structures were preserved. Cell clumps of 2-15 cells were often found; cells in such clumps often appeared to be all relaxed or all contracted. Isolated single cells contracted to KCl elevation or to norepinephrine up to 49 or 37% of initial length, EC50 values for contraction by norepinephrine and KCl were 0.4 microM and 40 mM, respectively; norepinephrine maximum contraction was about 35% less than that for KCl. Lightly loaded spirally cut strips from carotid artery were also studied. EC50 values for norepinephrine and KCl were 4 microM and 40 mM and unaffected by removal of the endothelium. Again, maximum contractions to norepinephrine were less than those to KCl. Contraction speeds were similar for isolated cells and intact strips. However, relaxation of maximally contracted isolated cells did not occur within 10 min. We conclude that canine carotid artery smooth muscle cells can be isolated with little structural or functional damage. The large number of gap junctions between cells and the tendency for cells to be isolated in small groups connected by gap junctions suggests that these cells would be useful for study of cell-to-cell coupling between arterial muscle cells.

Animals↗