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Biomedical subjects

G M Carlson

Publications and source records attributed to G M Carlson.

At least 73 records · Page 4Linked to original sources
PubMed1980

Alteration of myoelectric activity of small intestine by invasive Escherichia coli.

Invasive strains of Escherichia coli (4608-58 and TD 213 CL) altered myoelectric activity of the small intestine in New Zealand White rabbits. The altered myoelectric activity had two distinct complex patterns. The first was defined as repetitive bursts of action potentials (RBAPs) that occurred predominantly in infected ligated ileal loops. The RBAP activity is characterized by action potential discharge activity greater than 1.5 s in duration and occurring on three or more successive slow waves on the same electrode recording site. These bursts of action potentials often migrated to adjacent electrode sites. The second complex pattern, defined as the migrating action potential complex (MAPC), occurred predominantly in the uninfected small intestine orad to the ligated ileal loop. The MAPC consists of action potential discharge activity of 2.5 s or longer that propagates aborally over at least two consecutive electrode sites. These studies demonstrated an altered myoelectric pattern, the RBAP, characteristic of invasion within the infected ligated loop. The MAPC, characteristic of noninvasion, was noted in the uninfected proximal small intestine.

Action Potentials↗
PubMed1980

Shigella dysenteriae I enterotoxin: proposed role in pathogenesis of shigellosis.

Bacterial strains of Shigella dysenteriae I (3818-T and 3818-O) and Shigella enterotoxin altered myoelectric activity of the small intestine in New Zealand White rabbits. These agents were compared with activity caused by sterile culture broth or sterile saline. The altered myoelectric activity was characterized by two distinct complexes: repetitive bursts of action potentials (RBAP), characteristic of invasive strains of bacteria, and the migrating action potential complex (MAPC), characteristic of noninvasive bacteria. RBAP activity was the predominant myoelectric complex observed with S. dysenteriae strain 3818-T, an invader and toxin producer; S. dysenteriae strain 3818-O, a noninvader and toxin producer; and by Shigella enterotoxin. MAPC activity was present but was significantly less in all cases. These studies of the small intestine demonstrate an alteration in myoelectric activity characterized principally by RBAP activity indicative of invasion.

Action Potentials↗
PubMed1978

A vicinal dithiol containing an essential cysteine in phosphoenolpyruvate carboxykinase (guanosine triphosphate) from cytosol of rat liver.

The highly purified form of phosphoenolpyruvate carboxykinase (PEPCK) contained 13 thiols (all in the reduced state) per 72 000 daltons. Modification of the enzyme with equimolar 5,5'-dithiobis(2-nitrobenzoate) (Nbs2) caused rapid formation of a cystine disulfide bridge and an even more rapid loss of enzymatic activity. Formation of the cystine bridge proceeded about 25 times faster than formation of the analogous intramolecular disulfide of dithiothreitol induced by Nbs2. o-Iodosobenzoate, Cd2+, and the 2,3-dimercapto-1-propanol complex of arsenite were potent, time-dependent, irreversible inhibitors of PEPCK. The inactivation by arsenite-2,3-dimercapto-1-propanol and o-iodosobenzoate was first order with respect to both time and inhibitor concentration. The sum of these data indicates the existence in PEPCK of a critical cysteine that is in a vicinal dithiol grouping with a second cysteine. PEP protected against cystine bridge formation induced by equimolar Nbs2 but not against the extent of inactivation. In the presence of PEP, the modification by Nbs2 of one cysteine/mol of enzyme (k = 1.2 X 10(6) M-1 min-1 at pH 7.2) caused nearly complete inactivation. Replacing the bulky 5-thio-2-nitrobenzoate moiety with cyanide did not result in any reactivation. This critical, cyanylated cysteine was determined to be 44% of the distance from the amino terminus.

Animals↗
PubMed1978

Effect of toxigenic Escherichia coli on myoelectric activity of small intestine.

When exposed to cholera toxin (CT), distal ileal loops of the rabbit small intestine showed an alteration in myoelectric activity. This alteration was defined as the migrating action potential complex (MAPC). The purpose of this study was to determine, using myoelectric recording techniques, the effects of live toxigenic Escherichia coli (TEC) on motility. Live TEC, live nontoxigenic E. coli (NTEC), and culture filtrates of these organisms were studied. Live TEC and its filtrate induced MAPC activity similar to that of CT. Live TEC induced a mean of 3.8 MAPCs/h, significantly greater than induced by live NTEC. TEC filtrate induced a mean of 14.2 MAPCs/h, significantly greater than NTEC filtrate. Heating the TEC filtrate to 100 degrees C before use resulted in a significant decrease of MAPC activity. This experiment demonstrated that live TEC and its culture filtrate altered ileal myoelectric activity. The effect may have been mediated by a heat-labile enterotoxin. This study suggests that alterations in small intestinal motility may be important in the pathogenesis of TEC diarrhea.

Action Potentials↗
PubMed1978

Ricinoleic acid effect on the electrical activity of the small intestine in rabbits.

Using myoelectric recording techniques, we examined the myoelectric effects of castor oil; ricinoleic acid (cis isomer), the active ingredient of castor oil; and ricinelaidic acid (trans isomer) in the small intestine of New Zealand white rabbits. Ricinoleic acid, 2 microgram/kg per min (6mM), was perfused into a distal 12-cm ileal loop. An abnormal myoelectric pattern developed that was similar to the alteration in the electrical activity that has previously been reported for cholera enterotoxin. Castor oil, 0.85 ml/kg, had a similar effect. Ricinelaidic acid, 2 microgram/kg per min, induced no activity. A second preparation consisted of an intraluminal perfusion of ricinoleic acid, 2 microgram/kg per min, into the first section of the duodenum. The abnormal myoelectric pattern was observed in the jejunum and the ileum but not the duodenum. The mean onset time for the development of this altered myoelectric state for all experiments was 3.5 h. These studies suggest that an active motility component in addition to the secretory state exists throughout the small intestine that is exposed to castor oil or ricinoleic acid.

Action Potentials↗
PubMed1977

Human colonic myoelectric activity in response to prostigmin and the gastrointestinal hormones.

Colonic myoelectric activity was determined using a mucosal clip electrode in normal human subjects, in the basal state and following the administration of prostigmin, pentagastrin, cholecystokinin, or secretin. Slow-wave activity was present 49 +/- 3.0% of the recording time and occurred at two frequencies, 6.5 +/- 0.1 cycles/min and 3.5 +/- 0.1 cycles/min, in the rectum. Spike potentials were infrequent in the basal state. Prostigmin, pentagastrin, or cholecystokinin did not affect the slow-wave activity or frequency, but these agents significantly increased the number of spike potentials (P less than 0.05). Secretin had no effect on myoelectric activity. The electrode system was tested in the cat and showed excellent correlation of the myoelectric activity between the mucosal clip electrode and a serosal electrode. These studies indicate: (1) a mucosal clip electrode provides an accurate method of recording colonic myoelectric activity when compared to a serosal electrode in the cat; (2) in man, slow-wave activity is present only intermittently and exists at two frequencies, approximately 6 cycles/min and 3 cycles/min; (3) gastrointestinal hormones and prostigmin increase spike potential discharge without altering slow-wave activity or frequency.

Adult↗
PubMed1977

Migrating action potential complex of cholera: a possible prostaglandin-induced response.

Distal ileal loops of New Zealand white rabbits exposed to cholera toxin demonstrated the presence of a highly organized myoelectric pattern defined as the migrating action potential complex (MAPC). We investigated the mechanism by which cholera enterotoxin stimulates MAPC activity. Certain anti-inflammatory drugs have altered the secretory component of cholera diarrhea. We investigated effects of these anti-inflammatory drugs on the MAPC. Indomethacin, 5.0 mg/kg iv, abolished all MAPC activity. Indomethacin, 1.5 mg/kg iv, or acetylsalicylic acid, 150 mg/kg given intragastrically, altered propagation velocity and at times its direction of propagation, but did not abolish the MAPC. An infusion of prostaglandin F2alpha, 2 microng/kg per min intraluminally, induced MAPC activity similar to that of the cholera complex. Indomethacin, 5.0 mg/kg iv, produced no significant changes in number of complexes or propagation velocity. These observations suggested that inhibition of the cholera complex by indomethacin may result from the alteration of prostaglandin synthesis and that prostaglandins may initiate the motility component of cholera diarrhea.

Action Potentials↗
PubMed1977

Evidence that abnormal myoelectrical activity produces colonic motor dysfunction in the irritable bowel syndrome.

Although the irritable bowel syndrome is characterized as an abnormality in colonic motor activity occurring in response to certain stimuli, the etiology of this disorder is unclear. The purpose of this study is to determine the relationship of altered slow wave activity and the abnormal motility of the distal colon seen in patients with the irritable bowel syndrome. Myoelectrical activity was recorded using a bipolar electrode clipped to the distal colonic mucosa and motor activity was measured by perfused catheters. Colonic slow waves and contractions were present at two frequencies, 6 and 3 cycles per min. The slow wave frequency seemed to determine the frequency of colonic motor activity. Patients with the irritable bowel syndrome had increased 3-cycle per min slow wave activity in the basal state (P less than 0.001). However, no difference in basal 3-cycle per min motor activity was present between the two groups (P greater than 0.05). When colonic motor activity was increased with cholecystokinin or pentagastrin, patients with irritable bowel syndrome showed a marked increase in 3-cycle per min contractile activity, occurring simultaneously with 3-cycle per min slow wave activity. These studies suggest that increased colonic 3-cycle per min slow wave activity in patients with the irritable bowel syndrome may be the basic abnormality that leads to colonic motor dysfunction in response to various physiological stimuli.

Adult↗
PubMed1976

Stimulation of phosphorylase kinase autophosphorylation by peptide analogs of phosphorylase.

Autoactivation of phosphorylase kinase in the presence of substrates has been studied to determine the cause of the hysteresis, or lag, in the phosphorylase kinase reaction. Peptide analogs corresponding to the convertible serine region of phosphorylase have been used as low molecular weight alternative substrates. Autophosphorylation of the kinase molecule was measured under conditions that favored autoactivation. Phosphorylase b and a tetradecapeptide, which was found to be a good model of phosphorylase, stimulated autoactivation by 86- and 37-fold, respectively. The tetradecapeptide also stimulated autophosphorylation of subunits A and B of the kinase molecule. This increased autophosphorylation coincided with an increased ability to convert phosphorylase. This finding supports the hypothesis that autophosphorylation is responsible for the lag in the phosphorylase kinase reaction. No evidence was obtained to suggest that the lag could be due to dissociation of the kinase. The stoichiometry of phosphate incorporation into phosphorylase kinase subunits by autophosphorylation was much greater than that reported to occur by protein kinase phosphorylation. Multiple phosphorylation sites in subunit A accounted for most of the phosphate incorporation during autophosphorylation. Saturating levels of hexa- and octapeptide analogs also caused stimulation of autophosphorylation. Possible mechanisms and experimental implications of substrate-stimulated autophosphorylation are discussed. Consideration also is given to the possible role of effectors in autophosphorylation in vivo.

Animals↗
PubMed1976

Site of action and biphasic effect of neutral salts in the phosphorylase kinase reaction.

The inhibition of phosphorylase kinase catalytic activity by 0.1 M neutral salts was predicted by the Hofmeister series of anions. The site of action of the salts was determined by the following evidence to be on the phosphorylase kinase molecule directly, rather than on its protein substrate. (1) Nonactivated kinase was more sensitive to salt inhibition than the activated form. (2) Ca2+ partially overcame the inhibition of nonactivated kinase. (3) Inhibition by Cl- occurred with either phosphorylase or a tetradecapeptide containing the convertible seryl residue as substrate. (4) Phosphorylation of nonactivated phosphorylase kinase by protein kinase was markedly inhibited by NaNO3, but this salt had little effect on the phosphorylation of histone by protein kinase. The influence of neutral salts on phosphorylase kinase activity was biphasic. Although activity was inhibited at low salt concentrations, it actually was stimulated as the salt concentration was increased. A similar biphasic response to various salt concentrations was observed in the velocities of autophosphorylation of phosphorylase kinase. The lag in the rate of product formation seen during the activity assay was less pronounced at inhibitory salt concentrations and was abolished at stimulatory salt concentrations. How the influence of salts relates to autophosphorylation and the lag is considered.

Animals↗
PubMed1976

Intestinal myoelectric activity in response to live Vibrio cholerae and cholera enterotoxin.

The myoelectric response of the rabbit ileum was studied in response to live Vibrio cholerae culture, a whole cell lysate of cholera, and the purified enterotoxin. Each cholera preparation produced a series of highly organized migrating action potential complexes (MAPC). An MAPC was defined as action potential discharge with a duration of 2.5 s or longer, followed by similar activity on at least one other consecutive electrode site. The mean and modal onset time of MAPC activity occurred 4 h after the infection with live Vibrio cholerae culture, the freeze-dried whole cell lysate preparation, or the purified enterotoxin. After the onset of activity this pattern persisted for the duration of the recording period (up to 12 h). The MAPC had a mean propagation velocity of 0.85+/-0.07 cm/s (mean+/-SEM), which remained constant with time. Direct visual observation of the loop revealed that the MAPC's resulted in contractions that propelled intraluminal contents in an aborad direction. The mean fluid output from the 12-cm ileal loops was 6.4+/-1.1 ml/h (mean+/-SEM). Control experiments consisted of recordings from: (a) a ligated ileal loop into which nothing was placed; (b) a ligated ileal loop into which either uninfected culture broth or 0.9% NaCl solution was injected; (c) a ligated ileal loop infused with 0.9% NaCl solution at a rate of 11.2 ml/h, and (d) rapid injection of 1.0, 2.5, 5.0, or 10.0-ml boluses of 0.9% NaCl into the proximal catheter. MAPC activity was not observed in any of the control experiments. These studies indicate that in addition to a secretory component to cholera, there exists a highly organized MAPC that results in contractions that propel intraluminal contents in an aborad direction.

Action Potentials↗
PubMed1976

Colonic myoelectric activity in the irritable bowel syndrome.

Although the irritable bowel syndrome has been characterized as an abnormality in colonic motor activity occurring in response to certain stimuli, the etiology of this abnormality is unclear. The purpose of this study was to compare colonic myoelectric and motor activity in normal subjects and in patients with the irritable bowel syndrome. Myoelectric activity was recorded using a bipolar electrode clipped to the mucosa of the rectal and rectosigmoid areas. Basic electrical rhythm (BER), spike potential activity, and intraluminal pressure were recorded in both groups. Two types of BER were observed. The major component of the BER had a frequency of approximately 6 cycles per min, whereas the minor component had a frequency of approximately 3 cycles per min. Although both types of BER were recorded in the two groups, thitable bowel syndrome. The 3 cycles per min activity was present as 44.1 +/- 1.3% of the total BER in the irritable bowel syndrome, as compared with 10.0 +/- 1.6% in the normal group (P less than 0.001). Basal spike potential and motor activity were similiar in both groups. Because it had been demonstrated previously that colonic responsiveness to certain stimuli was increased during the slower frequency BER, it is suggested that the abnormalities in colonic motor response reported in the irritable bowel syndrome may be related to this difference in colonic BER.

Adult↗
PubMed1976

Normal abomasal electromyography and emptying in sheep and the effects of intraabomasal volatile fatty acid infusion.

Electromyographic activity and emptying of the abomasum were studied in 3 sheep. Pacesetter potentials (PP), with a frequency of 6.06 +/- 0.05 (X +/- SEM) cycles/minute and propagated distally with an increased conduction velocity approaching the pylorus, were recorded from the distal 11 cm of the antrum. Spike burst and fused action potentials (AP) were superimposed on a variable percentage of PP. The aborad propagation of both types of AP was associated with abomasal emptying at the net rate of 12.61 +/- 1.38 (X +/- SEM) ml/minute. Intraabomasal infusion of 50 ml of a 300 mM solution of either acetic, propionic, or butyric acid was associated with a marked decrease in abomasal AP activity and in the emptying rate. Butyric acid was most effective, followed by propionic and acetic acids. The importance of the results in relation to the pathogenesis of left displaced abomasum (LDA) in dairy cows was noted.

Abomasum↗