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Biomedical subjects

R K Goyal

Publications and source records attributed to R K Goyal.

At least 127 records · Page 7Linked to original sources
PubMed1992

Both ATP and the peptide VIP are inhibitory neurotransmitters in guinea-pig ileum circular muscle.

1. Intracellular membrane potential recordings were made from circular smooth muscle cells of the guinea-pig ileum in the presence of atropine (1 microM) and nifedipine (0.1 microM) at 30 degrees C. 2. Perfusion with adenosine triphospate (ATP, 100 microM) and vasoactive intestinal peptide (VIP, 2 microM) resulted in membrane hyperpolarizations of 6.4 +/- 0.3 and 6.8 +/- 0.3 mV, respectively. Picospritzes of ATP (10 mM in pipette) and VIP (100 microM in pipette) resulted in membrane hyperpolarizations of 6.9 +/- 0.4 and 6.3 +/- 0.4 mV, respectively. 3. The ATP-induced hyperpolarizations were antagonized by alpha, beta-methylene ATP desensitization (100 microM for 30 min) and the ATP antagonist Reactive Blue 2 (200 microM), but were unaffected by the VIP antagonist VIP 10-28 (1 microM). 4. The VIP-induced hyperpolarizations were antagonized by VIP 10-28, but unaffected by alpha, beta-methylene ATP desensitization and Reactive Blue 2. 5. A single pulse of transmural nerve stimulation (2 ms, 15 mA) resulted in an inhibitory junction potential (IJP) that reached a maximal amplitude of 12.9 +/- 0.5 mV at 378 +/- 20 ms from the stimulus. This fast IJP was abolished by apamin (2 microM) or tetrodotoxin (1 microM), antagonized by alpha, beta-methylene ATP desensitization or Reactive Blue 2, but unaffected by VIP 10-28. 6. In the presence of apamin (1 microM), four pulses of transmural stimulation (2 ms, 20 Hz, 15 mA) resulted in an IJP that reached a maximal amplitude of 4.8 +/- 0.2 mV at 1.4 +/- 0.1 s from the stimulus. This slow IJP was antagonized by tetrodotoxin (1 microM) or VIP 10-28 (1 microM), augmented by Reactive Blue 2 (200 microM), and unaffected by alpha, beta-methylene ATP desensitization. 7. These findings provide evidence that both ATP and VIP are inhibitory neurotransmitters in the circular muscle layer of the ileum and that ATP may be the neurotransmitter responsible for the fast IJP and VIP the neurotransmitter responsible for the slow IJP.

Adenosine Triphosphate↗
PubMed1992

Role of chloride ions in lower esophageal sphincter tone and relaxation.

Studies were performed in strips of opossum lower esophageal sphincter (LES) muscle in vitro. External Cl(-)-free Krebs solution (0[Cl-]o) inhibited resting tone. Treatment with the Cl- channel blocker diphenylamine-2-carboxylate (DPC, 0.3-100 microM) caused a concentration-dependent relaxation of LES muscle, as did treatment with 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS, 1 microM-3 mM), a Cl(-)-HCO3- exchange blocker, and bumetanide (0.3-100 microM), a blocker of the Na(+)-K(+)-2Cl- cotransport. DIDS and bumetanide are also known to cause Cl- channel block. The calculated pD2 and Emax values for DPC, DIDS, and bumetanide were 5.24 +/- 0.28 (n = 5), 3.38 +/- 0.16 (n = 5), and 4.49 +/- 0.23 M (n = 5), and 78.80 +/- 5.38, 74.80 +/- 6.54, and 83.70 +/- 10.20%, respectively. The neuronal Cl- channel activators gamma-aminobutyric acid and glycine had no effect on the resting tone. DPC, DIDS, and bumetanide appear to have acted directly on smooth muscle rather than indirectly through the release of inhibitory neurotransmitters because LES relaxation by these agents was not influenced by tetrodotoxin (10 microM), which blocks action potentials in nerves, or by omega-conotoxin (1 microM), which inhibits the release of neurotransmitters from nerve terminals. LES muscle relaxed by exposure to 0[Cl-]o, DPC, DIDS, and bumetanide contracted with the addition of carbachol (30 microM); muscle so treated was resistant to the inhibitory neurotransmitter-mediated relaxation ordinarily induced by electrical field stimulation (EFS, 0.12-32 Hz). This effect was not nonselective, as the EFS-resistant muscle relaxed fully with isoproterenol (0.1-100 microM). HCO(3-)-free Krebs in the nominal absence of CO2 did not affect the resting tone and its relaxation. The Ca2+ channel blocker nifedipine decreased resting tone but did not antagonize the relaxation of carbachol-contracted muscle induced by either EFS or isoproterenol. These studies suggest that Cl- may play an important role in LES tone and relaxation due to inhibitory neurotransmitter released from intramural nerves.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Differential sensitivity to bradykinin of esophageal distension-sensitive mechanoreceptors in vagal and sympathetic afferents of the opossum.

1. Single-unit activity was recorded from afferent fibers in the cervical vagus and thoracic sympathetic nerves in the opossum. Seventy-six fibers that responded to balloon distension (100 mmHg for 10 s) of the smooth muscle portion of the esophagus were selected for further study. 2. Forty-nine distension-sensitive afferents were identified in the vagus nerve. The stimulus response function (SRF) of 41 fibers behaved as "low-threshold mechanoreceptors" (LTM), with mean threshold value of 0.29 +/- 0.17 mmHg and saturation pressure of 50-70 mmHg. All fibers demonstrated background activity, with a mean rate of 8.83 +/- 0.93 imp/s (range 0.5-31.25). 3. Twenty-seven distension-sensitive afferents were identified in the thoracic sympathetic chain (T6-T8) and splanchnic nerve. The SRF study revealed two types of fibers: 1) a wide-dynamic-range mechanonociceptor (WDRMN) with a mean response threshold of 3.43 +/- 0.90 mmHg (n = 15) and 2) a "high-threshold mechanonociceptor" (HTMN) with a mean response threshold of 34.93 +/- 2.70 mmHg (n = 12). The mean background activities of WDRMN and HTMN fibers were 0.5 +/- 0.13 and 0.20 +/- 0.08 imp/s, respectively. Both of these fibers had saturation pressures of > 120 mmHg. 4. The conduction velocities were measured in 14 LTM, 10 WDRMN, and seven HTMN fibers. The mean conduction velocity of LTM fibers was 5.03 +/- 1.35 m/s (range 0.97-18.00), with five unmyelinated "C"-fibers (< 2.5 m/s) and nine A-delta fibers (> 2.5 m/s). The mean conduction velocity of WDRMN fibers was 3.64 +/- 0.84 m/s (range 1.10-8.25), consisting of five C-fibers and five A-delta fibers. The mean conduction velocity of HTMN fibers was 6.22 +/- 2.35 m/s (range 1.73-24.66); three fibers were unmyelinated C-fibers, and four fibers were A-delta fibers. 5. The sensitivity to bradykinin (BK) administered systemically (1-300 micrograms/kg) was tested in LTM (n = 34), WDRMN (n = 15), and HTMN (n = 8) fibers. Twenty-six (66%) LTM fibers responded to BK, and eight (34%) fibers were insensitive to BK. All 15 WDRMN and eight HTMN fibers tested responded to BK. 6. Tachyphylaxis to repeated application of BK was tested in all three classes of fibers. The vagal LTM fibers did not exhibit tachyphylaxis when BK was given at an intervals of 10 min. The sympathetic WDRMN and HTMN fibers demonstrated partial tachyphylaxis when BK was injected at 10-min intervals, but not when BK was injected at 20-min intervals.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Peptidergic innervation of the human esophageal smooth muscle.

Studies were performed to define the peptidergic nature of intramural nerves in the human esophagus. Cryosections of uninvolved surgically resected tissues from 14 individuals were studied by immunofluorescence for the localization of 10 neuropeptides. Myenteric neurons showed bombesin-, calcitonin gene-related peptide-, galanin-, substance P-, vasoactive intestinal polypeptide-, leucine-enkephalin-, methionine-enkephalin-, neuropeptide Y-, and somatostatin-like immunoreactivity. Submucous neurons had all the above except neuropeptide Y, methionine-enkephalin, leucine-enkephalin, and bombesin. Both groups of neurons received nerve terminations positive for calcitonin gene-related peptide, galanin, neuropeptide Y, substance P, and vasoactive intestinal polypeptide. Myenteric neurons additionally received terminations positive for neuropeptide Y, methionine-enkephalin, and somatostatin. All muscle layers had varicose fibers that reacted for calcitonin gene-related peptide, galanin, neuropeptide Y, and substance P. Longitudinal and circular muscle received few nerves reactive for leucine-enkephalin, whereas methionine-enkephalin was localized in a few nerve endings in the circular muscle. Somatostatin- and bombesin-reactive nerves occurred in longitudinal muscle. No cholecystokinin-reactive nerves were found. This study extends the results of previous studies and shows the previously undescribed presence of calcitonin gene-related peptide- and galanin-reactive nerves in the human esophagus and identifies neuropeptides that may serve as motor, sensory, and modulatory neurotransmitters of esophageal nerves.

Adult↗
PubMed1991

Localization of calcitonin gene-related peptide in human esophageal Langerhans cells.

Previously undescribed calcitonin gene-related peptide-immunoreactive intraepithelial cells were seen in specimens of esophageal mucosa obtained by biopsy or surgical resection from 14 individuals. These calcitonin gene-related peptide-immunoreactive cells were sparsely seen in normal mucosa but increased markedly in esophagitis. They were inaccessible to routine histological stains, but osmication showed them as dendritic forms resembling Langerhans cells of the skin. Their cytological identity was determined with immunocytochemical tests for human antigenic markers such as Ia, HLA-DR, and OKT6 for Langerhans cells, Leu-M5 and Leu-M3 for intraepithelial macrophages, CD3 and TCR-1 for T-lymphocytes, Leu-14 for B-lymphocytes, S-100 for Merkel cells, and chromogranin for amine precursor uptake and decarboxylation cells. Double localization showed that calcitonin gene-related peptide immunoreactivity colocalized with Ia, HLA-DR, and OKT6 but not with the other markers. These studies show that intraepithelial Langerhans cells in the esophageal mucosa contain calcitonin gene-related peptide, which may serve as an immunomodulator.

Calcitonin Gene-Related Peptide↗
PubMed1991

The nature of noncholinergic membrane potential responses to transmural stimulation in guinea pig ileum.

The effect of substance P antagonism on membrane potential responses to transmural nerve stimulation in the presence of atropine was examined in circular smooth muscle of the guinea pig ileum. Intracellular recordings of membrane potential responses recorded 3-5 mm oral to the transmural stimulus consisted of an inhibitory junction potential followed by two distinct depolarizations referred to as early and late excitatory junction potentials. Substance P antagonism was achieved by desensitization with high doses of substance P or use of the antagonist Spantide (Sigma Chemical Co., St. Louis, MO). Substance P antagonism had no effect on the amplitude of the inhibitory junction potential, caused an increase in the latter portion of the early excitatory junction potential, and abolished the late excitatory junction potential. The excitatory junction potential potentiated by substance P receptor antagonism was associated with a decrease in membrane resistance, increased in amplitude with conditioning hyperpolarizations to the estimated equilibrium potential for K+, and was blocked by the Cl-/HCO3- exchange inhibitor DIDS or prolonged perfusion with low-chloride solution. These studies suggest that a noncholinergic, non-substance P neurotransmitter is released from enteric motoneurons that produces excitation through an increase in smooth muscle chloride conductance.

Analgesics↗
PubMed1991

Chloride-mediated junction potentials in circular muscle of the guinea pig ileum.

Junction potentials were recorded from circular muscle cells of the guinea pig ileum at various sites oral and anal to a transmural stimulus in the presence of atropine, apamin, and substance P antagonism (desensitization) at 30 degrees C. A short train of pulses produced an inhibitory junction potential (slow IJP), which preceded an excitatory junction potential (slow EJP). The slow IJP was observed up to 56.4 +/- 2.9 mm oral and 65.4 +/- 2.2 mm anal to the stimulus. The slow EJP was observed up to 50.4 +/- 1.9 mm oral and 58.3 +/- 2.1 mm anal to the stimulus. Hexamethonium (400 microM) decreased the amplitudes of the slow IJP and slow EJP at all sites. After hexamethonium, the slow IJP was observed up to 37.3 +/- 2.3 mm oral and 39.8 +/- 2.1 mm anal to the stimulus and the slow EJP was 44.2 +/- 2.5 mm oral and 43.3 +/- 2.6 mm anal to the stimulus. The slow IJP and slow EJP were associated with an increase and decrease in membrane resistance, respectively. Conditioning depolarizations of the circular muscle cells reduced the amplitudes of the slow IJP and slow EJP. Both were abolished at a membrane potential of approximately -25 mV. Conditioning hyperpolarizations increased the amplitude of both the slow IJP and slow EJP. Ionic substitution experiments with low external chloride solution (12.4 mM) resulted in an immediate increase in slow IJP and slow EJP amplitudes, whereas more prolonged perfusion resulted in a significant decrease in slow IJP and slow EJP amplitudes. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (400 microM) resulted in decreases in slow IJP and slow EJP amplitudes. These results suggest that the slow IJP and slow EJP are due to a decrease and increase in membrane chloride conductance, respectively. The noncholinergic neural pathways responsible for the slow IJP and slow EJP extend approximately 40 mm orally and anally along the longitudinal axis of the guinea pig ileum.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Chloride-mediated inhibitory junction potentials in opossum esophageal circular smooth muscle.

Intracellular recordings were made from circular smooth muscle cells of the opossum esophagus. Inhibitory junction potentials (IJPs) 8.3 +/- 0.7 mV in amplitude were observed in response to a single pulse (1 ms, 15 mA) of transmural nerve stimulation. Potassium channel blockers apamin (1 microM), tetraethylammonium (10 mM), 4-aminopyridine (250 microM), and cesium chloride (10 mM) did not reduce IJP amplitude. Conditioning hyperpolarizations to the equilibrium potential for potassium were associated with a significant increase in IJP amplitude. A small increase in membrane resistance was observed during the IJP. Changes in external potassium concentration had no significant effect on IJP amplitude acutely. However, prolonged perfusion with potassium-free Krebs solution resulted in a marked decrease in IJP amplitude as did prolonged perfusion with ouabain (0.1 mM). Low-chloride solution (12.4 mM) resulted acutely in an increase in IJP amplitude. Prolonged low-chloride perfusion resulted in a significant decrease in IJP amplitude. The anion exchange chloride channel inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (600 microM) significantly reduced IJP amplitude. These findings suggest that the IJP observed in opossum esophageal circular smooth muscle in response to a single pulse of stimulation is due to a decrease in membrane chloride conductance. The ability of prolonged application of Na-K pump inhibitors to abolish the IJP appears to be due to known secondary effects of these agents in depleting intracellular chloride.

Animals↗
PubMed1991

Effects of bradykinin and bradykinin analogs on the opossum lower esophageal sphincter: characterization of an inhibitory bradykinin receptor.

Bradykinin (BK) caused the circular muscle of opossum lower esophageal sphincter to relax and then contract in vitro. The effects of BK were not modified by indomethacin, tetrodotoxin, omega-conotoxin, atropine, propranolol, phentolamine, haloperidol, methysergide, pyrilamine or cimetidine. Apamin but not tetraethylammonium antagonized the inhibitory effect of BK and nifedipine antagonized its excitatory effect. Structure-activity relationships of 10 BK analogs known to be active on BK receptors were studied. Six analogs had distinct excitatory response profile and the rank order of potency of these agonists according to pD2 (shown in parentheses) was D-Arg-[Hyp3Thi5,8D-Phe7]-BK (6.49 +/- 0.19) greater than [Thi5,8D-Phe7]-BK (5.61 +/- 0.26) greater than Lys-Lys-[Hyp3-Thi5,8D-Phe7]-BK (5.45 +/- 0.14) greater than BK (5.16 +/- 0.20) greater than [des-Arg9]-BK (4.95 +/- 0.08) greater than [D-Phe7]-BK (4.73 +/- 0.10). However, only BK was fully efficacious (100%) and Emax values of all the analogs were less than that of BK. On the inhibitory response BK was the only agonist (pD2 = 5.48 +/- 0.08) and none of the BK analogs were agonist. All the BK analogs were also inactive as antagonists except Lys-Lys-[Hyp3-Thi5,8D-Phe7]-BK and Lys-Lys-[Hyp2,3-Thi5,8D-Phe7]-BK which competitively and selectively antagonized the BK inhibitory response. The pA2 value of Lys-Lys-[Hyp3-Thi5,8D-Phe7]-BK was 6.92 +/- 0.17.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Mucosal peptidergic innervation of the opossum esophagus and anal canal: a comparison with snout skin.

Nerves within and under the esophageal epithelium of the opossum esophagus were investigated morphologically with osmication and immunohistochemically for ten neuropeptides. The structurally similar but functionally diverse epithelia of the anal canal and snout skin, on which no immunohistochemical information exists, were similarly investigated for comparison. Total innervation was estimated from osmication, which revealed intraepithelial nerves in all three tissues in the following order of density: snout skin greater than anal canal greater than esophagus. Calcitonin gene-related peptide and substance P occurred in all three organs. The snout skin had intraepithelial galanin nerves but not vasoactive intestinal polypeptide, while conversely the esophagus and anal canal had vasoactive intestinal polypeptide but not galanin. All peptides found intraepithelially also occurred subepithelially. Calcitonin gene-related peptide, galanin, neuropeptide Y, substance P and vasoactive intestinal polypeptide subepithelial nerves occurred in all the tissues, while gastrin releasing peptide nerves occurred infrequently in the subepithelial regions of the esophagus and anal canal, but not the snout skin. As these epithelia neither secrete nor absorb, their nerves are presumably sensory. The peptides investigated could not account for all intraepithelial nerves demonstrated by osmium. Differences in the innervation of these epithelia may result from their differing sensory requirements.

Anal Canal↗
PubMed1990

Stimulus-response function studies of esophageal mechanosensitive nociceptors in sympathetic afferents of opossum.

1. Single-unit activity was recorded from afferent fibers in either the paravertebral sympathetic chain or the splanchnic nerves. Forty-three fibers that responded to distension of the smooth-muscle portion of esophagus were selected for further study. 2. Out of the 43 fibers, 27 (62%) had ongoing resting activity, and 16 (38%) were silent. The mean resting activity of these fibers was 0.28 +/- 0.06 imp/s (range, 0-2.6 imp/s). 3. Repeated distensions of the esophagus to a fixed pressure (80 mmHg) evoked spike discharge at a reproducible rate. There was no evidence of facilitation or inhibition of subsequent responses. The mean coefficient of variation (CV) was 0.17 +/- 0.05 imp/s (n = 5). 4. The stimulus-response function (SRF) to intraluminal graded distension was studied in 35 fibers. Thirty-three fibers showed linear increase in firing that did not saturate up to 120 mmHg. Two fibers reached maximal discharge rate at 60 mmHg. The mean discharge rate at 120 mmHg pressure was 14.87 +/- 1.52 imp/s. 5. Threshold pressure for activation of each fiber was calculated by a least-squares linear-regression plot of the SRF. The threshold pressure varied from 0 to 50 mmHg (mean, 16.21 +/- 2.86 mmHg). The distribution profile of the threshold values showed that there were two separate populations of mechanosensitive receptors: 1) wide-dynamic-range mechanonociceptors (WDR-MN) with mean threshold pressure of 2.89 +/- 0.75 mmHg (range, 0-7 mmHg; n = 22); and 2) high-threshold mechanonociceptors (HT-MN) with mean threshold of 33.26 +/- 2.52 mmHg (range, 19-50 mmHg; n = 13). 6. Discharge evoked by esophageal peristalsis was studied in five WDR-MN and five HT-MN units. Whereas all five WDR-MN units (threshold value, 2.6 +/- 0.96 mmHg) responded to peristalsis, none of the HT-MN units (threshold value, 31.2 +/- 4.01 mmHg) did so. The mean response to peristaltic contraction in WDR-MN units was 5.32 +/- 1.36 imp/s, which was 24.7% of the maximal response (21.53 +/- 1.92 imp/s; n = 5) at 120 mmHg. The duration of evoked response to peristaltic contraction was 10-12 s. 7. The activity profile of the units to 60-s balloon distension at near threshold and higher pressures showed three patterns: 1) rapid adaptation, 2) slow adaptation, and 3) slow adaptation with after discharge. The rapidly adapting fibers became slowly adapting with greater degrees of esophageal distension. The units that showed rapid or slow adaptation at low-distension pressure became indistinguishable from one another at high-distension pressure.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Effect of bradykinin on opossum esophageal longitudinal smooth muscle: evidence for novel bradykinin receptors.

Bradykinin (BK) produced a concentration-dependent contraction of the longitudinal but not the circular muscle of the opossum esophagus. The pD2 value of BK on the longitudinal muscle was 6.58 +/- 0.06 M. The maximal response of the longitudinal muscle to BK was 44% compared to carbachol. The putative B1 agonist des-Arg9-BK produced contraction of longitudinal muscle but the putative B1 receptor antagonist des-Arg9-[Leu8]-BK (20 and 50 microM) did not modify the responses to BK or des-Arg9-BK. The putative B2 antagonists d-Phe7-BK, Thi5,8-d-Phe7-BK and d-Arg0-Hyp3-Thi5,8-d-Phe7-BK (B6572) were found to be agonists in this tissue. The rank order of potency with respect to Emax obtained from cumulative concentration-response curves was BK greater than Thi5,8-d-Phe7-BK greater than B6572 greater than d-Phe7-BK and pD2 values of these compounds were 6.58 +/- 0.06, 6.30 +/- 0.28, 6.74 +/- 0.08 and 5.05 +/- 0.04 M, respectively. The excitatory effect of BK and Thi5,8-d-Phe7-BK was not modified by tetrodotoxin (1 and 10 microM), atropine (1 microM) or indomethacin (1 and 10 microM), but was significantly (P less than .001) inhibited by nifedipine (1 and 10 microM). Three putative "tissue selective" BK antagonists, d-Phe2,7-BK (B4404), d-Phe7-Hyp8-BK and Phe2-d-Phe7-BK also had an agonistic effect on longitudinal muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Synthesis and pharmacological study of antihyperlipaemic activity of 2-substituted thieno(2,3-d)pyrimidin-4(3H)-ones.

A series of 2-substituted thieno(2,3-d)pyrimidin-4-(3H) ones (1-15) was prepared by the reaction of thiophene ortho-aminoester (IV) with a variety of nitriles (V) under acidic conditions, and screened for antihyperlipaemic activity in various animal models. While most of these compounds were found active, 2-chloromethyl-5,6,7,8-tetrahydrobenzo(b)thieno(2,3-d) pyrimidin-4(3H)-one (5) was found to be the most active of all. The serum triglyceride lowering activity exhibited by 5 was found comparable to that of clofibrate and riboflavin tetrabutyrate. Compound 5 was also found to be safe as indicated by acute and chronic toxicity studies in mice and rats.

Animals↗