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Biomedical subjects

H J Cooke

Publications and source records attributed to H J Cooke.

At least 127 records · Page 7Linked to original sources
PubMed1987

Vasoactive intestinal polypeptide actions on the guinea pig intestinal mucosa during neural stimulation.

Electrical stimulation of the mucosal innervation of the guinea pig ileum results in an increase in chloride secretion that is mediated in part by excitation of muscarinic cholinergic receptors on enterocytes. This study investigated the involvement of vasoactive intestinal peptide in the cholinergic and noncholinergic phases of the secretory response evoked by electrical stimulation of submucosal neurons in the guinea pig ileum. Flat sheets of ileum set up in Ussing flux chambers responded to exogenous vasoactive intestinal peptide by an increase in baseline short-circuit current which was reduced by furosemide and by vasoactive intestinal peptide antiserum. When submucosal neurons were electrically stimulated, a biphasic change in short-circuit current was evoked. Vasoactive intestinal peptide, forskolin, and isobutylmethylxanthine enhanced the cholinergic portion of the response, whereas the antiserum prevented or reduced the effects of the peptide but not of forskolin. In the presence of atropine to eliminate the cholinergically mediated response, vasoactive intestinal peptide reduced the noncholinergic phase of the response and its action was prevented by the antiserum. Vasoactive intestinal peptide enhanced the increase in short-circuit current evoked by the muscarinic agonist bethanechol. These results demonstrate that vasoactive intestinal peptide and other substances that stimulate secretion by increasing cyclic 3',5'-adenosine monophosphate levels in enterocytes potentiate the calcium-dependent, cholinergic phase of the chloride secretory response evoked by neural stimulation of the guinea pig ileum. No evidence was found for vasoactive intestinal peptide as the mediator of the noncholinergic phase of the response.

Animals↗
PubMed1987

Neuropeptide modification of chloride secretion in guinea pig distal colon.

This study examined the effects of electrically stimulating submucosal neurons in the guinea pig isolated distal colonic mucosa and determined the effects of several peptides that are present in these neurons. Electrical field stimulation of muscle-stripped segments of guinea pig distal colonic mucosa, set up in Ussing flux chambers, evoked an increase in short-circuit current (Isc), of 371 +/- 31 MicroA.cm-2. The response to electrical stimulation was abolished by tetrodotoxin and significantly reduced by serosal furosemide. Atropine reduced, but did not abolish, the neurally evoked response. Addition of neuropeptide Y and galanin to the serosal bath had no effect on baseline Isc, but both evoked a concentration-dependent decrease in the neurally evoked secretory response. Vasoactive intestinal polypeptide evoked a concentration-dependent increase in basal (unstimulated) Isc that was reduced by furosemide and unaltered by tetrodotoxin. Neuropeptide Y, but not galanin, significantly reduced the secretory responses to vasoactive intestinal polypeptide and bethanechol. Somatostatin 201-995 and human calcitonin gene-related peptide had no effect on basal Isc nor did either alter the neurally evoked response. These results suggest that acetylcholine and non-cholinergic neurotransmitter(s) stimulate chloride secretion in the guinea pig distal colonic mucosa. This neurosecretory response may be modulated by neuropeptide Y and galanin that are found within submucosal neurons.

Animals↗
PubMed1987

Epithelial responses evoked by stimulation of submucosal neurons in guinea pig distal colon.

The influence of submucosal neurons on ion transport in the guinea pig distal colon was examined in muscle-stripped sheets of submucosa-mucosa set up in Ussing flux chambers. Spontaneous variations in potential differences (PD) and short-circuit current occurred ranging from positive currents associated with luminal negative PDs to negative currents with luminal positive PDs. Basal current in both groups was reduced by mucosal amiloride. In tissues with positive or negative short-circuit currents, unidirectional mucosal-to-serosal sodium fluxes were greater than serosal-to-mucosal fluxes and small net absorptive fluxes were present. Little or no chloride secretory flux was present. Electrical stimulation of submucosal neurons evoked a tetrodotoxin-sensitive increase in short-circuit current in tissues with positive or negative short-circuit currents. This was due to an increase in net chloride flux and little change in net sodium flux or residual flux. The increase in net chloride flux was due almost entirely to an increase in serosal-to-mucosal chloride flux and was associated with an increase in total tissue conductance. The stimulus-evoked response was reduced by atropine. These results suggest that stimulation of submucosal neurons that innervate the distal colonic epithelium evokes a large chloride secretory response that is due in part to release of acetylcholine at neuro-enterocyte junctions.

Amiloride↗
PubMed1987

Muscarinic receptor subtypes mediating the mucosal response to neural stimulation of guinea pig ileum.

Muscarinic receptors involved in the secretory response evoked by electrical stimulation of submucosal neurons were investigated in muscle-stripped flat sheets of guinea pig ileum set up in flux chambers. Neural stimulation produced a biphasic increase in short-circuit current due to active chloride secretion. Atropine and 4-diphenylacetoxy-N-methylpiperadine methiodide (4-DAMP) (10(-7) M) were more potent inhibitors of the cholinergic phase of the response than was pirenzepine. Dose-dependent increases in base-line short-circuit current were evoked by carbachol and bethanechol; 4-hydroxy-2-butynyl trimethylammonium chloride (McN A343) produced a much smaller effect. Tetrodotoxin abolished the effects of McN A343 but did not alter the responses of carbachol and bethanechol. McN A343 significantly reduced the cholinergic phase of the neurally evoked response and caused a rightward shift of the carbachol dose-response curve. All muscarinic compounds inhibited [3H]quinuclidinyl benzilate binding to membranes from mucosal scrapings, with a rank order of potency of 4-DAMP greater than pirenzepine greater than McN A343 greater than carbachol greater than bethanechol. These results suggest that acetylcholine released from submucosal neurons mediates chloride secretion by interacting with muscarinic cholinergic receptors that display a high binding affinity for 4-DAMP. Activation of neural muscarinic receptors makes a relatively small contribution to the overall secretory response.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
PubMed1987

Telomeres of the human X and Y chromosomes.

Analysis of the nature of the DNA sequences at the telomeres of the short arms of the human sex chromosomes suggests parallels with the structures found at telomeres of a number of lower eukaryotes. The exact nature of the end of the DNA has not yet been established but it is clear that there are multiple levels of variability both between and within individuals in this region of the genome.

DNA↗
PubMed1987

Cholinergic receptors mediating secretion in guinea pig colon.

This study examined the role of cholinergic receptors in mediating the chloride secretory response evoked by stimulation of enteric neurons in muscle-stripped segments of mucosa from guinea pig distal colon set up in flux chambers. Basal short-circuit current was not altered by tetrodotoxin, hexamethonium or muscarinic antagonists. The neurally evoked response was not altered by hexamethonium, but was reduced by muscarinic antagonists with a rank order of potency: atropine = 4-diphenyl acetoxy-N-methylpiperidine greater than pirenzepine. 1,1-Dimethyl-4-phenyl-piperazinium iodide increased resting short-circuit current above basal levels. Carbachol and bethanechol evoked a concentration-dependent increase in short-circuit current that was reduced by tetrodotoxin. The effects of carbachol were antagonized by hexamethonium, 4-diphenyl acetoxy-N-methylpiperidine and pirenzepine. Competition for [3H]quinuclidinyl benzilate binding indicated a rank order of potency of 4-diphenyl acetoxy-N-methylpiperidine greater than pirenzepine greater than carbachol greater than bethanechol. These studies indicate that cholinergic and noncholinergic transmission play a significant role in regulation of chloride transport in the guinea pig distal colon. Both nicotinic and muscarinic receptors on neurons that project to the mucosa as well as epithelial muscarinic receptors are mediators of the chloride secretory response.

Animals↗
PubMed1986

Submucosal nerves and cholera toxin-induced secretion in guinea pig ileum in vitro.

The effects of cholera toxin on intestinal transport parameters were examined in muscle-stripped flat sheets of guinea pig ileum in order to determine whether the effects were partly mediated by stimulation of the mucosal innervation. Cholera toxin evoked an increase in short-circuit current that reflected active ion secretion. Tetrodotoxin completely blocked neurally mediated responses to electrical field stimulation, but it did not prevent the effects of cholera toxin. In the absence of tetrodotoxin, electrical stimulation of submucosal neurons evoked a biphasic increase in short-circuit current that was produced by chloride secretion. The first phase, which was known to be cholinergic, was enhanced by cholera toxin. These results suggest that cholera toxin may mediate intestinal secretion by direct action on the enterocytes as well as by enhancing cholinergically mediated intestinal secretory processes.

Animals↗
PubMed1985

Nerve-mediated action of forskolin on guinea pig ileal mucosa.

The effects of forskolin on myenteric neuronal activity and mucosal function were examined in guinea pig ileum. Forskolin increased the excitability of myenteric neurons, and increased mucosal chloride secretion by stimulating enteric neurons as well as by acting directly on enterocytes.

Animals↗
PubMed1985

Pharmacological analysis of 5-hydroxytryptamine actions on guinea-pig ileal mucosa.

The possibility that 5-hydroxytryptamine (5-HT) is involved in the chloride secretory response evoked by electrical stimulation of submucosal neurons was investigated in guinea-pig ileum set up in Ussing flux chambers. When electrical stimulus pulses of 0.5 ms duration, amplitude of 3.2 mA and frequency of 10 Hz were applied repetitively in the plane of the tissue, a biphasic increase in short-circuit current (Isc) occurred. After tachyphylaxis to 5-HT or when the 5-HT antagonist cisapride was present in the bathing solutions, electrical stimulation of enteric nerves still evoked a biphasic change in Isc that was similar in magnitude to the response before either treatment. Cisapride (5 microM) prevented the mucosal response to exogenous 5-HT without altering the functional integrity of the tissues. Addition of 100 microM 5-HT to the submucosal side of the tissue evoked a biphasic increase in Isc that reflected primarily chloride secretion. Tetrodotoxin and atropine significantly reduced but did not abolish the change in Isc and chloride secretion. These results suggest that the mucosal response evoked by electrical field stimulation is not mediated by release of 5-HT at neuro-enterocyte junctions or from endocrine elements. 5-Hydroxytryptamine activated enteric cholinergic neurons within the submucosal plexus to stimulate chloride secretion.

Animals↗
PubMed1985

An estimate of unique DNA sequence heterozygosity in the human genome.

Fifteen different restriction fragment length polymorphisms (RFLPs) were detected in the human genome using 19 cloned DNA segments, derived from flow-sorted metaphase chromosomes or total genomic DNA, as hybridization probes. Since these clones were selected at random with respect to their coding potential, their analysis permitted an unbiased estimate of single-copy DNA sequence heterozygosity in the human genome. Since our estimate (h = 0.0037) is an order of magnitude higher than previous estimates derived from protein data, most of the polymorphic variation present in the genome must occur in non-coding sequences. In addition, it was confirmed that enzymes containing the dinucleotide CpG in their recognition sequence detect more polymorphic variation than those that do not contain CpG.

Base Sequence↗
PubMed1985

Mucosal responses evoked by stimulation of ganglion cell somas in the submucosal plexus of the guinea-pig ileum.

The effects of electrical field stimulation and tetrodotoxin on the mucosal secretory response were compared in guinea-pig ileal mucosa with and without the submucosal plexus. Short-circuit currents and transmural electrical potential differences were similar in ganglionated and aganglionated tissues. Total tissue conductance was greater after removal of the submucosal ganglia. Electrical field stimulation evoked a tetrodotoxin-sensitive increase in short-circuit current in ganglionated tissues, and little or no response in aganglionated tissues. Both ganglionated and aganglionated tissues responded similarly to carbachol, vasoactive intestinal polypeptide, scorpion venom and alanine. These results suggest that electrical field stimulation of guinea-pig ileum evokes an increase in short-circuit current that reflects chloride secretion by exciting ganglion cell bodies whose axons project to the transporting cells and/or endocrine cells. Direct electrical activation of enteroendocrine cells is not a factor in the stimulus-evoked secretory response.

Action Potentials↗
PubMed1984

Chromosome assignment of two cloned DNA probes hybridizing predominantly to human sex chromosomes.

In situ hybridization experiments were carried out with two clones, YACG 35 and 2.8, which had been selected from two genomic libraries strongly enriched for the human Y chromosome. Besides the human Y chromosome, both sequences strongly hybridized to the human X chromosome, with few minor binding sites on autosomes. In particular, on the X chromosome DNA from clone YACG 35 hybridized to the centromeric region and the distal part of the short arm (Xp2.2). On the Y chromosome, the sequence was assigned to one site situated in the border region between Yq1.1 and Yq1.2. DNA from clone 2.8 also hybridized to the centromeric region of the X and the distal part of the short arm (Xp2.2). On the Y, however, two binding sites were observed (Yp1.1 and Yq1.2). The findings indicate that sex chromosomal sequences may be localized in homologous regions (as suggested from meiotic pairing) but also at ectopic sites.

Animals↗
PubMed1984

The use of cloned Y chromosome-specific DNA probes for fetal sex determination in first trimester prenatal diagnosis.

Prenatal diagnosis by chorion biopsy in the first trimester of pregnancy has advantages over second trimester amniocentesis because diagnosis can be achieved at 9-12 weeks gestation, reducing prenatal anxiety and avoiding the trauma of late abortion. DNA can be prepared from chorionic villus biopsies in sufficient quantity and purity for use in prenatal diagnosis systems using specific DNA probes hybridised to restriction endonuclease digests. DNA probes derived from the Y chromosome have been used to determine fetal sex. The use of such probes means that the chromosomal sex of the fetus can be identified more quickly than by chromosome preparation and more accurately than by sex chromatin staining, and has the additional advantage that the same DNA preparation can be used for other diagnostic tests. A dot hybridisation method has been successfully used to provide even more rapid results than conventional hybridisation to Southern blots of restriction endonuclease digests. There is a risk that Y chromosome-specific DNA probes for sex determination may be subject to error if the parents have extreme Y chromosome variants such as a small or non-fluorescent Y or a Y autosome chromosome translocation. The precise extent to which such chromosome variants may lead to error has been investigated. Even extreme Y chromosome variants totally lacking fluorescence were identified as male by the cloned probes used. However, Y autosome translocations carried by females could cause error if not identified in the parents. The value of the probes has been confirmed provided that parental chromosomes and DNA are examined in parallel with the chorionic biopsy material.

Cloning, Molecular↗
PubMed1984

Influence of enteric cholinergic neurons on mucosal transport in guinea pig ileum.

Electrical field stimulation was used to activate enteric neurons in the guinea pig ileum in order to determine the involvement of intramural cholinergic motor neurons in the control of mucosal sodium and chloride transport. Rectangular, bipolar stimulus pulses evoked a tetrodotoxin-sensitive biphasic increase in short-circuit current (Isc) that was due to an increase in active chloride secretion without any effect on active sodium absorption. During activation of enteric neurons, atropine, in concentrations of 5 X 10(-8) M or higher, reversibly abolished the rapid phase of the Isc and reduced the maximum sustained response to 40-50% of control values. Atropine reduced chloride secretion evoked by electrical stimulation and had no effect on sodium fluxes. Basal rates of sodium and chloride transport and tissue conductances were not altered by atropine. When muscarinic receptors were maximally stimulated with 10(-5) M carbachol, activation of enteric nerves increased Isc to 46% of control values. Bethanechol and eserine increased base-line Isc, and this effect was blocked by atropine but not by tetrodotoxin. The increase in Isc evoked by bethanechol was due to an increase in active chloride secretion. These results show that acetylcholine released by activation of enteric cholinergic motor neurons acts as muscarinic receptors on enterocytes to stimulate chloride secretion.

Acetylcholine↗
PubMed1984

Histamine action on guinea pig ileal mucosa.

Nerve-mediated and direct actions of histamine on mucosal transport function in the guinea pig ileum were investigated. Addition of histamine to the serosal side of flat sheet preparations in Ussing chambers evoked a transient increase in base-line short-circuit current that was due primarily to an increase in active chloride secretion. The mucosal response to histamine was mimicked by the H1-receptor agonist 2-methylhistamine, but not by the H2-receptor agonist dimaprit. The histamine-evoked response was prevented by the H1-receptor blocker pyrilamine, but not by the H2-receptor antagonist cimetidine. Thirty percent of the mucosal response to histamine was inhibited by tetrodotoxin. Intracellular electrical recording showed that histamine activated AH/type 2 myenteric neurons, and this response was abolished in the presence of pyrilamine. Local anesthetic action of pyrilamine was ruled out by direct electrical recording from myenteric neurons in the presence and absence of pyrilamine. Electrical field stimulation evoked a biphasic increase in short-circuit current. Histamine and 2-methylhistamine did not alter the sustained phase of the short-circuit current response to electrical field stimulation, although pyrilamine reduced the electrically evoked response by 22%. Muscarinic blockade with atropine reduced the stimulus-evoked response by 55%. When muscarinic receptors were blocked and electrical field stimulation applied, histamine increased the stimulus-evoked mucosal response by 22.3%. These results suggest that histamine increases short-circuit current and chloride secretion by acting at H1-receptor sites on both the enteric innervation of the mucosa and on the enterocytes.

Animals↗