Biomedical subjects

J L Conklin

Publications and source records attributed to J L Conklin.

At least 73 records · Page 4Linked to original sources

PubMed1991

Nitric oxide: mediator of NANC hyperpolarization of opossum esophageal smooth muscle.

Activation of intrinsic nonadrenergic noncholinergic (NANC) esophageal nerves during peristalsis or by electrical field stimulation (EFS) in vitro produces a hyperpolarization followed by a depolarization of the circular smooth muscle of the opossum esophagus. N omega-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide synthase, and nitric oxide (NO) were used to test the hypothesis that NO or a NO-containing compound is a mediator of this NANC nerve-induced hyperpolarization of circular esophageal smooth muscle. The transmembrane potential difference of esophageal circular smooth muscle cells was recorded with glass microelectrodes. Nerve-mediated membrane responses were evoked by single electrical pulses of 0.5 ms duration and 50 V amplitude. L-NNA abolished the initial hyperpolarization and reduced the amplitude of and the time to maximal depolarization. L-Arginine (1 mM), the substrate for NO synthase, antagonized the effect of L-NNA. Exogenous NO produced hyperpolarization of the smooth muscle membrane potential and attenuated the amplitudes of EFS-induced hyperpolarization and depolarization. The effect of NO was blocked neither by L-NNA nor by tetrodotoxin (1 microM). The data support the hypothesis that NO or a NO-containing compound mediates NANC nerve-induced responses of the esophageal smooth muscle membrane.

Amino Acid Oxidoreductases↗

PubMed1990

Pathways of slow-wave propagation in proximal colon of cats.

Colonic slow waves (SWs) are generated by nonneuronal cells located at the interface of the submucosa and muscularis propria. It has been proposed that SWs arise from a complex of nerves, interstitial cells of Cajal, and smooth muscle found at this location. These experiments test the hypothesis that the propagation of colonic SWs depends on an intact interface between the submucosa and muscularis propria. The electromyogram was recorded from segments of the proximal colon of the cat. All intact tissues generated SWs that propagated in the long and circumferential axes of the colon. Tetrodotoxin did not disrupt SW propagation in either axis. Transection of tissues between recording sites interrupted the spread of SWs in both axes. Transection of the submucosa disrupted the longitudinal spread of SWs, whereas transection of the muscularis propria did not. Removing the submucosa from the midportion of tissue segments oriented in the long axis of the colon resulted in a loss of SWs from the segment devoid of submucosa. Transection of the submucosa of tissue segments oriented in the circular axis of the colon did not disrupt circumferential propagation of SWs. Dissecting a 1-cm-wide segment of submucosa from the midportion of such a circularly oriented tissue did not disrupt the circumferential spread of SWs, and SWs were recorded from the muscle segment that was devoid of submucosa. SWs were not recorded from the segment devoid of submucosa when it was isolated from adjacent intact segments. The data support the hypothesis that the regeneration of SWs during their longitudinal propagation takes place at the interface between the submucosa and muscularis propria.

Animals↗

PubMed1989

Origin of slow waves in the isolated proximal colon of the cat.

Slow oscillations of the membrane potential difference of circular smooth muscle cells of the colon, slow waves, arise at the interface between the submucosa and muscularis externa of the colon. These studies test the hypothesis that the generation of slow waves in the circular muscle layer of the colon of the cat is dependent upon an intact interface between the submucosa and muscularis externa. Electrical recordings were made from 3 types of tissue preparations from the proximal colon: (a) submucosa and muscularis externa intact, (b) submucosa isolated from the circular muscle, and (c) muscularis externa isolated from the submucosa. The cellular make-up of each tissue was determined by the osmic acid-zinc iodide method (Champy-Maillet), and the Masson's trichrome stain. Continuous slow waves were recorded from intact tissues. Removal of the submucosa abolished slow waves from the underlying muscularis externa. Either irregular electrical transients or waxing and waning slow wave-like activity were recorded from the isolated submucosa. Submucosal tissues removed from the muscularis externa contained no circular smooth muscle, but did contain elements of the plexus submucosus extremus.

Animals↗

PubMed1981

Radiation-induced recurrent intestinal pseudo-obstruction.

The syndrome of intestinal pseudo-obstruction is a complex of signs and symptoms of intestinal obstruction without evidence of mechanical obstruction of the intestinal lumen. A patient with radiation-induced intestinal pseudoobstruction is described. The patient is a 74-year old woman with a history of chronic diarrhea, recurrent episodes of crampy abdominal pain, nausea and vomiting since receiving a 13,000 rad radiation dose to the pelvis in 1954. She has been hospitalized on many occasions for symptoms and signs of bowel obstruction. Upper gastrointestinal contrast roentgenograms with small bowel follow-through done during these episodes revealed multiple dilated loops of small bowel with no obstructing lesion. Barium enemas revealed no obstructing lesion. Each episode resolved with conservative therapy. Other secondary causes for intestinal pseudo-obstruction were ruled out in our patient. She gave no history of familial gastrointestinal disorders. Although postirradiation motility abnormalities have been demonstrated experimentally this is the first report of radiation induced intestinal pseudo-obstruction.

Aged↗

PubMed1979

Some determinants of latency of off-response to electrical field stimulation in circular layer of smooth muscle of opossum esophagus.

Transverse strips from smooth muscle of opossum esophagus were subjected to electrical field stimulation of intramural nerves to study the latency of the off-response. Latency is the time from the end of the stimulus train to the beginning of the off-response. Latency increased from one end of the smooth muscle segment to the other; it was shortest proximally and longest distally. Variables altering this latency gradient were sought. Strip width and tension had no effect (P greater than 0.02). Longer stimulation trains shortened latency (P less than 0.02). Krebs solution was modified by changing potassium concentration and by the addition of: hexamethonium, 1 x 10(-4) M; D-tubocurarine, 1 x 10(-4) M; bethanechol, 5 x 10(-7) M; carbachol, 5 x 10(-7 M; physostigmine, 1 x 10(-7) M; propranolol, 1 x 10(-6) M; tolazoline, 5 x 10(6) M; norepinephrine, 1 x 10(-5) M; isoproterenol, 1 x 10(-6) M; and dopamine, 1 x 10(4) M. Increased potassium concentrations shortened latency, and decreased potassium concentrations lengthened it (P less than 0.02). Carbachol, bethanechol, physostigmine, and isoproterenol shortened latency (P less than 0.02). Hexamethonium, D-tubocurarine, tolazoline, propranolol, norepinephrine, and dopamine had no effect (P greater than 0.02).

Animals↗

PubMed1977

A potassium gradient in smooth muscle segment of the opossum esophagus.

Sodium and potassium content were determined in the smooth muscle segment of the opossum esophagus. Extracellular space measurements were also made using inulin and mannitol as markers. The muscle also made using inulin and mannitol as markers. The muscle was sampled at five sites spaced equally along the esophageal segment. On site in the stomach was also examined. The mean tissue sodium content was 36.6 +/- 10.7 meg/kg, and the mean tissue sodium content was 83.5 +/- 2.9 meg/kg wet wt. The mean inulin space was 184 +/- 34 ml/kg, and the mean mannitol space was 249 +/- 20 ml wet wt. The tissue potassium content was found to decline from 48.4 /- 10.1 meg/kg at the proximal site to 23.6 +/- 8.0 meg k/g at the distal site. The slope of electrolyte values from sites 1 through 5 was significant for both potassium and sodium. Extracellular space volume did not differ significantly from one end of the smooth muscle segment to the other.

Animals↗

PubMed1975

Immunochemical staining of the rat adenohypophysis in organ culture.

Rat anterior pituitaries were cytologically studied following cultivation in organ culture, with and without the addition of hypothalamic and cortical extracts. Although five distinct cell types could be identified with classical stains in the uncultivated glands, the peroxidase-labeled antibody technique (using antibodies against STH, LTH, FSH, LH and TSH) showed that not all of the immune-specific cell types were being identified with the classical stains. This discrepancy was magnified following culture as chromophilic cells seen with classic stains decreased in number with an increase in culture time. The peroxidase technique, however, revealed that all cells remained constant in type and number regardless of time in culture. While the addition of either hypothalamic or cortical extract to the culture medium produced cytological alterations demonstrated by the classical dyes, the antibody technique showed no such alterations. Such a comparison of staining techniques emphasizes the hazards of relying solely on histological procedures to reveal the hormonal activity of the pituitary gland.

Animals↗

PubMed1975

Local specialization at ileocecal junction of the cat and opossum.

In 10 cats and 10 opossums, serial transverse strips of muscularis propria 2 mm wide, from about 1.5 cm above to about 1.5 cm below the ileocecal mucosal junction, were separately stretched to discover the relationship between length and tension and were separately subjected to electrical field stimulation. In both species, ileal strips showed stimulus relaxations, sometimes accompanied by contractions after the stimulus trains (off responses), whereas colonic strips generally did not. These responses were abolished by tetrodotoxin, 3 times 10-7 M in the opossum, 3 times 10-6 M in the cat. Length-tension slopes were greatest just above the ileocecal junction where stimulus relaxation occurred. Tetrodotoxin at 3 times 10-7 M raised basal tension in ileal strips in both species and in colonic strips only in the cat. Muscle of the ileocecal junction resembles that of the esophagogastric and gastroduodenal junctions in showing a relatively high degree of resistance to stretch and prominent neurogenic stimulus relaxation. However, the ileocecal junction, in contrast, also possesses a tonic inhibitory innervation.

Animals↗

PubMed1973