Biomedical subjects

K M Sanders

Publications and source records attributed to K M Sanders.

At least 235 records · Page 13Linked to original sources

PubMed1988

Effects of vitamin D3 and IFN-gamma on the synthesis of the second complement component, C2, by a human myeloid leukemia (HL-60) cell line.

HL-60 cells, a human promyelocytic cell line, can be induced to differentiate along either monocytic or granulocytic pathways. The production of the second complement component, C2, is a marker of monocytic differentiation and can be up-regulated by cytokine stimulation. We studied the effects of IFN-gamma and vitamin D3, two factors previously shown to induce monocytic differentiation of HL-60 cells, on C2 production and C2 mRNA content. We found that HL-60 cells produce little if any C2 but can be induced to synthesize C2 by IFN-gamma. Vitamin D3 pretreatment followed by IFN-gamma stimulation resulted in earlier and greater production of C2. HL-60 cells did not contain detectable amounts of C2 mRNA unless they were stimulated with IFN-gamma. Pretreatment with vitamin D3 followed by IFN-gamma stimulation resulted in a 147% increase in C2 mRNA content compared with IFN-gamma stimulation alone. These results indicate that the up-regulation of C2 production by IFN-gamma and vitamin D3 is pretranslational although additional posttranslational effects were not excluded. C2 production by these cells is a useful marker of monocytic differentiation.

Cell Line↗

PubMed1988

Influence of prostaglandins on electrical and mechanical activities of gastric muscles of Bufo marinus.

1. Study was performed to compare the role of prostaglandins in regulating gastric contractile activity in an amphibian model, Bufo marinus, with mammalian models. 2. The prostaglandin synthesis inhibitor, indomethacin, had little effect on spontaneous mechanical activity, but increased the force and frequency of contractions stimulated by acetylcholine. 3. PGE2 reversed the effects of indomethacin and reduced the force and frequency of contractions. These effects were concentration-dependent. 4. Intracellular measurement of membrane potential demonstrated that the effects of PGE2 could be explained by basic effects on membrane potential and slow wave activity. 5. The data shown that many similarities exist between amphibian and mammalian gastric muscles in terms of the regulatory role played by endogenous PGs. It also appears that the mechanisms of PGE2 action are similar.

Acetylcholine↗

PubMed1988

Role of sodium pump in membrane potential gradient of canine proximal colon.

A large gradient in membrane potential exists through the thickness of the circular layer in canine colonic muscles. This study tested the effects of several experimental manipulations known to block electrogenic sodium pumping on the resting potentials of colonic muscles. Membrane potentials were recorded with microelectrodes from cells through the circular muscle layer. In cells adjacent to the submucosal surface of the circular layer, application of ouabain (10(-6) to 10(-5) M) caused an average membrane depolarization of 36 mV. Removal of the external K+ resulted in depolarizations similar to the effect of ouabain. Readmission of K+ (5.9 mM) produced repolarization and an additional hyperpolarization that averaged 13 mV beyond the resting potential. When exposed to 15 mM K+, cells hyperpolarized well beyond the estimated potassium equilibrium potential (EK). Ouabain blocked the repolarization in response to reintroduction of external K+. Lowering the bath temperature to 20 degrees C rapidly depolarized membrane potential; rewarming repolarized cells. Ouabain and K+-free solutions blocked the repolarization response to rewarming. Cells also depolarized when exposed to solutions in which the NaCl was replaced with LiCl. Membrane potentials of cells within the bulk of the circular layer decreased as a function of distance from the submucosal border. Cells at the myenteric border of the circular muscle were not significantly affected by ouabain and K+-free solution, but these treatments abolished the gradient in membrane potential across the circular layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Effects of membrane potential on electrical slow waves of canine proximal colon.

The effects of membrane potential on the waveforms and propagation of slow waves were tested using circular muscles of the canine colon. Studies were conducted with intracellular recording techniques on cross-sectional strips of canine proximal colon. Circular muscle cells near the submucosa generated slow waves that decayed in amplitude as they spread through the circular layer. The membrane potentials of cells were less negative as a function of distance from the submucosal border. Cells near the submucosa were depolarized with elevated external K+ and electrical pulses using the partitioned chamber technique. The waveforms of depolarized submucosal cells were compared with events recorded from cells in the bulk of the circular layer. The waveform changes caused by experimental depolarization were different from the changes in waveform that occur during propagation, suggesting the latter are due to a different mechanism than depolarization. The effects of the membrane potential on syncytial input resistance and length constant were also evaluated. The results of these studies are consistent with the hypothesis that slow-wave propagation across the circular layer in canine proximal colon occurs passively.

Animals↗

PubMed1987

Effects of gold sodium thiomalate on interferon stimulation of C2 synthesis and HLA-DR expression by human monocytes.

Gamma-interferon (gamma-IFN) is a T cell-derived lymphokine that has potent macrophage-activating properties. It increases Fc receptor density, increases the formation and release of reactive oxygen intermediates, increases the synthesis and release of complement cascade proteins, especially C2 and factor B, and increases class II (HLA-DR) antigen expression. These effects may play a role in the potentiation of inflammation in rheumatoid arthritis. We examined the possibility that gold sodium thiomalate (GST), an effective treatment for rheumatoid arthritis, would inhibit gamma-IFN-mediated stimulation of monocyte/macrophages. GST in concentrations attainable in vivo was shown to inhibit both spontaneous and gamma-IFN-stimulated C2 production up to 50%. GST inhibition could be only partially overcome with increasing concentrations of gamma-IFN. In addition, GST inhibited gamma-IFN-stimulated HLA-DR expression at the highest concentrations tested (20-50 micrograms/ml). GST alone in low concentrations (0.1-5 micrograms/ml) was found to increase HLA-DR antigen expression as quantitated by several methods, including flow cytometry, cell surface enzyme-linked immunosorbent assay, and Western blotting. This GST-stimulated increase in HLA-DR antigen expression paralleled an increased ability of monocytes to present antigen. The mechanism by which low concentrations of GST stimulate HLA-DR antigen expression is unclear, but was shown by 35S-methionine cell labeling not to involve increased HLA-DR protein synthesis.

Cell Separation↗

PubMed1987

Correlation of immunoglobulin and C reactive protein levels in ankylosing spondylitis and rheumatoid arthritis.

Serum C reactive protein (CRP), IgG, and IgA levels were measured in 22 patients with ankylosing spondylitis (AS) and in 20 patients with rheumatoid arthritis (RA) to study the regulation of these proteins in inflammatory disease states. In both RA and AS the mean CRP, IgG, and IgA levels were raised above normal values. Although IgA and CRP levels showed a significant positive correlation in RA (r = 0.53, p = 0.02), there was no correlation between these values in AS (r = 0.24, p = 0.29). The difference in correlation coefficients between the AS and RA groups was significant at a p = 0.05 level. In RA the raised IgA levels may be another manifestation of the acute phase response, as shown by the good correlation between IgA and CRP in that disease. In AS, however, the IgA levels, although raised, do not correlate with CRP levels, suggesting that the mechanism of increase of IgA in the two diseases is different. Gut mediated immune stimulation has been proposed as a cause of raised IgA levels in AS.

Adult↗

PubMed1987

Origin and propagation of electrical slow waves in circular muscle of canine proximal colon.

Experiments to determine the site of slow-wave origin and the mechanism of propagation were performed on muscles of the canine proximal colon. Cells along the submucosal border of the circular layer had resting membrane potentials (RMP) averaging -78 mV, and slow waves, 40 mV in amplitude. The RMP of cells through the thickness of the circular layer decreased exponentially with distance from the submucosal border, such that RMPs of circular cells at the myenteric border were only -43 mV. Slow waves decreased in amplitude through the thickness such that slow waves could not be detected adjacent to the myenteric border. When a thin strip of muscle along the submucosal border was removed, slow waves were not recorded from the bulk of the circular layer and could not be evoked by acetylcholine. Slow waves were still present in the excised strip. Experiments to determine the rate of slow-wave propagation were also performed. Two cells were impaled, one at the submucosal surface, and another at some distance through the circular layer. Slow waves occurred nearly simultaneously at both sites. What latency was observed could be explained on the basis of electrotonic conduction. The results support the hypothesis that in the canine proximal colon slow waves are generated at the extreme submucosal surface of the circular layer. The bulk of the circular layer does not possess either pacemaker or regenerative mechanisms, and slow waves propagate passively toward the myenteric border. The cable properties of the circular muscle syncytium furnish a barrier to invasion of the longitudinal layer by the slow wave event.

Acetylcholine↗

PubMed1987

Interaction of two electrical pacemakers in muscularis of canine proximal colon.

Experiments were performed to determine the source of the 20 cycles/min electrical oscillation commonly seen in colonic electrical records, the influence of the 20 cycles/min rhythm on the circular and longitudinal muscle layers, and the interactions between the 20 cycles/min rhythm and slow waves in circular muscle cells. Cross-sectional muscle preparations of the canine proximal colon were used to allow impalement of cells at any point through the thickness of the muscularis. Intracellular recordings from circular muscle cells clearly showed the two characteristic pacemaker frequencies in the colon (6 cycles/min slow waves; 20 cycles/min oscillations). The 20 cycles/min oscillations were recorded from longitudinal and circular muscle cells. Their amplitudes were greatest at the myenteric border. In the longitudinal layer the 20 cycles/min events initiated action potentials; in circular muscle the 20 cycles/min events summed with slow waves. Simultaneous recordings from circular and longitudinal cells across the myenteric border demonstrated that events in the two layers were usually in phase, suggesting that the two layers are electrically coupled and are paced by a common pacemaker. The amplitude of the 20 cycles/min events decayed with distance from the myenteric border in both circular and longitudinal muscles. The data demonstrate that two discrete populations of pacemaker cells generate the spontaneous electrical activity in the colon. Both events appear to passively spread through the circular muscle. It is the summation of these events that appears to serve as the signal for excitation-contraction coupling in circular muscle.

Animals↗

PubMed1986

Lymphokine stimulation of human macrophage C2 production is partially due to interferon-gamma.

Monocyte complement stimulator (MCS), a product of T lymphocytes, is defined by its ability to stimulate the synthesis and secretion of the second complement component (C2) by monocytes. Most macrophage-activating factor (MAF) activity present in lymphokine-rich culture supernatants has recently been found to be due to interferon-gamma (IFN-gamma). We therefore hypothesized that IFN-gamma may have MCS activity as well. We tested recombinant, E. coli-derived, human IFN-gamma (rIFN-gamma) for its effects on C2 production by adherent peripheral blood monocytes and U937 cells, a human monocytic cell line. Recombinant IFN-gamma in concentrations ranging from 0.1 to 300 U/ml (0.003 to 8.8 ng/ml) stimulates C2 production by both cell populations. Exposure of responding cells for at least 24 hr is required for maximal stimulation. To determine the contribution of IFN-gamma toward total MCS activity in crude lymphokine-rich supernatants, we employed a solid-phase immunoabsorption technique with the use of a monoclonal anti-IFN-gamma antibody. This technique removed all IFN-gamma detectable by a sensitive ELISA, but MCS activity was decreased by only 40 to 50%. Additionally, MCS activity of these supernatants did not correlate with IFN-gamma content as determined by ELISA. By using another method to eliminate IFN-gamma activity, acid dialysis destroyed all rIFN-gamma activity, as measured by stimulation of U937 C2 synthesis, but eliminated only 30 to 67% of MCS activity from crude lymphokine preparations. Thus IFN-gamma stimulates C2 production by monocytes and U937 cells and apparently accounts for some, but not all, MCS activity present in lymphokine-rich supernatants. Other lymphokines are present in such supernatants that also possess this activity.

Cell Line↗

PubMed1986

Effects of frequency on the wave form of propagated slow waves in canine gastric antral muscle.

Experiments were performed to test the effects of frequency on the wave form of electrical slow waves in canine antral circular muscle. At frequencies between 3.0 and 5.6 cycles per minute antral slow waves revealed an alternating wave form pattern. At physiological frequencies antral muscle was incapable of consistently propagating mechanically productive slow waves. Two components of the slow wave were identified on the basis of propagation refractory period. At inter-slow-wave intervals of 3-14 s, the amplitude and duration of the plateau phase wave decreased, but the upstroke phase of the slow wave was minimally affected. Intervals of 2.5-4 s resulted in a normal upstroke event but abolished the plateau. At shorter intervals the upstroke phase of the slow wave was greatly reduced or abolished. The absolute propagation refractory period averaged 2.8 +/- 0.9 s (n = 7) following repolarization of a 'conditioning' slow wave. Slow waves failed to propagate within the absolute propagation refractory period. Acetylcholine decreased the interval required for the plateau phase of the slow wave to recover and permitted conduction of mechanically productive slow waves at or above physiological frequencies. The data presented suggest that gastric motility is modulated by extrinsic and intrinsic factors which regulate slow-wave frequency.

Acetylcholine↗

PubMed1986

Enteric neural regulation of slow waves in circular muscle of the canine proximal colon.

The spontaneous electrical activities of circular muscle cells of the canine proximal colon were studied with intracellular micro-electrodes. All circular muscle cells exhibited slow waves at frequencies ranging between 2.8 and 7.0 cycles/min. The slow waves consisted of an upstroke phase followed by a plateau phase of variable duration (2-40 s). Many cells displayed a slow diastolic depolarization, or 'pre-potential' between slow waves. Slow waves spontaneously varied in duration and frequency in most preparations, creating distinctive slow wave patterns. Atropine, 2 X 10(-6) M, decreased the durations of slow waves in many preparations and often changed the pattern to a series of relatively uniform slow waves. A further reduction in mean slow wave duration was produced by additional treatment with tetrodotoxin, 10(-6) M. These results suggested that slow wave duration and pattern were affected by spontaneous discharge from both cholinergic and non-cholinergic excitatory nerves. Transmural nerve stimulation caused a short latency increase in slow wave duration (up to 38 s) that was abolished by atropine. In the presence of atropine, transmural stimulation evoked inhibitory junction potentials that reduced the amplitude and duration of the subsequent slow wave. The slow wave of reduced amplitude was followed by a slow wave of increased duration. The increase in duration of the slow wave did not appear to be related to the size of the preceding hyperpolarization, suggesting it was mediated by the release from non-cholinergic excitatory nerves. All responses to transmural stimulation were blocked by tetrodotoxin. Microejection of acetylcholine on to the muscle adjacent to the micro-electrode also produced an atropine-sensitive increase in slow wave duration. Tissues that had been stored in the cold overnight to reduce intrinsic neural activity exhibited regular slow waves of short duration. It is proposed that the basic myogenic pattern of spontaneous slow wave activity consists of regularly occurring slow waves of short duration (2-5 s). Intrinsic cholinergic and non-cholinergic excitatory nerves appear to modulate slow wave activity in vitro, producing distinctive slow wave patterns of variable instantaneous frequency and duration.

Acetylcholine↗

PubMed1986

Motoneurones of the submucous plexus regulate electrical activity of the circular muscle of canine proximal colon.

The hypothesis that the circular muscle of the canine proximal colon receives motor input from neurones in the submucous plexus was tested. Circular muscle cells were impaled with micro-electrodes and submucous plexus neurones were stimulated by electrical field stimulation and microejection of acetylcholine (ACh). In the presence of atropine to block the direct muscarinic effects, microejection of ACh onto the submucosa where intact submucous ganglia were suspended evoked: (i) an inhibitory junction potential (i.j.p.) that reduced the amplitude, duration and rate of rise of the subsequent slow wave; (ii) a slow wave of increased duration following the initial inhibitory response. These responses were enhanced by increasing the volume of ACh administered. Responses to ACh were blocked by hexamethonium, 10(-4) M; d-tubocurarine, 10(-4) M; or tetrodotoxin (TTX), 10(-6) M, suggesting they were neural in origin. Both inhibitory and excitatory responses were the result of non-cholinergic and non-adrenergic nerves. The transmitters mediating these effects are unknown. Removal of the longitudinal muscle, myenteric plexus, and the serosal portion of the circular muscle had no apparent effect on the responses to application of ACh to submucosal ganglia. In these preparations the responses to field stimulation were identical to those produced by ACh. The submucous plexus also provides cholinergic input to the circular muscle. When ACh was discretely applied to the submucosa cholinergic responses were elicited at the muscle cell which were significantly reduced by hexamethonium or TTX. These findings suggest that the cholinergic responses were the result of ACh release by neurones at the effector and not by overflow of the exogenous ACh. Cholinergic responses were also elicited in preparations in which the myenteric plexus had been removed. Slow waves in circular muscle of the proximal colon yield excitation-contraction coupling in the absence of Ca2+ action potentials. Therefore the influence of submucous neurones on electrical slow waves has direct consequences on motor activity. Reduction in the amplitude and duration of slow wave by i.j.p.s. results in reduction in the amplitude and duration of phasic contractions. Excitatory inputs enhance contractions. The data support a new concept: motoneurones emanating from submucous ganglia innervate the circular muscle and provide inhibitory and excitatory inputs to regulate slow wave activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗

PubMed1986

Passive and active membrane properties of canine gastric antral circular muscles.

Experiments were performed to determine the mechanisms responsible for the gradient of electrical activity within circular muscle of the canine gastric antrum. Cable properties of canine gastric antral circular muscles were determined using the partitioned chamber technique of Abe and Tomita (J. Physiol. Lond. 196: 87-100, 1968). The length constant of the circular muscle near the myenteric plexus was 2.4 mm. This was significantly greater than the length constant of the circular muscle near the submucosa (1.7 mm). Membrane time constants were determined by two techniques. Although the time constant of the circular muscle near the myenteric plexus tended to be greater than that of the circular muscle near the submucosa, this difference was not statistically significant. The two regions of circular muscle also differed in their relative levels of excitability. Submucosal circular muscles demonstrated considerably more outward rectification on depolarization and were difficult to bring to threshold for slow waves. This study demonstrates that significant differences exist in the passive and active membrane properties of myenteric and submucosal circular muscle cells. The data help explain the gradient of electrical activity through the thickness of antral circular muscle.

Animals↗

PubMed1985

Electrical basis for the effects of ethyl alcohol on canine gastric corpus muscles.

The effects of ethyl alcohol (EtOH) on membrane potential and slow wave activity were tested in strips of canine corpus circular muscle. Previous studies have shown that EtOH (0.1-1%) reduced the force and frequency of phasic contractions of corpus muscles and increased tone. It was the intention of this study to determine whether the mechanical effects were due to an electrical mechanism. Intracellular recordings revealed that EtOH hyperpolarized resting membrane potential and reduced the amplitude, duration and frequency of slow waves. These changes were concentration-dependent over the same range of EtOH concentrations that inhibited phasic mechanism activity. Simultaneous recordings of force and membrane potential demonstrated these effects. The tone produced by corpus muscles exposed to EtOH could not be explained by an electrical mechanism. The fact that membrane potential and several parameters of the slow wave depolarization are affected by EtOH might be explained by an increase in membrane conductance produced by EtOH.

Animals↗

PubMed1985

Slow wave heterogeneity within the circular muscle of the canine gastric antrum.

A cross-sectional preparation was designed in which multiple micro-electrodes can be precisely positioned to impale smooth muscle cells anywhere from the serosa to the submucosa. Intracellular electrical recordings were obtained from gastric antral circular muscle cells from the myenteric plexus to the submucosa. The resting membrane potential changed linearly as a function of distance from the myenteric plexus to the submucosa. Slow wave upstroke dV/dt, upstroke potential amplitude, and plateau potential amplitude changed linearly as a function of distance from the myenteric plexus to the submucosa. When slow waves were recorded simultaneously from a circular cell near the myenteric plexus and from a cell near the submucosa, the event always occurred first in the cell near the myenteric plexus. Electrical differences did not appear to be caused by electrotonic decay of slow waves as they propagated through the circular muscle. Electrical differences could not be explained on the basis of differences in intrinsic neural activity or prostaglandin synthesis. Membrane polarization could not explain the differences in slow waves between myenteric and submucosal circular muscle cells. The conclusion of this paper is that fundamental differences exist between the excitability mechanisms and/or passive membrane properties of cells near the myenteric plexus and the submucosa. These differences might be manifest in different motor performance of these two muscle cell populations.

Action Potentials↗

PubMed1985

Gradient in excitation-contraction coupling in canine gastric antral circular muscle.

Slow waves decay in amplitude as they propagate through the thickness of circular muscle of the canine antrum. Slow waves are the excitable events that initiate contractions in the antrum. Excitation-contraction coupling occurs if slow wave depolarizations surpass a 'mechanical threshold'. The amplitude of slow waves recorded from circular muscle cells near the submucosa was insufficient to reach the mechanical threshold previously determined for muscle near the myenteric plexus, suggesting that either submucosal cells are normally mechanically quiescent, or that contractions of submucosal cells are initiated at more polarized levels. Experiments were performed to determine the voltage-tension relationships in adjacent 'myenteric' and 'submucosal' circular muscles. Membrane potentials of the muscles were depolarized by elevated concentrations of potassium. Submucosal muscles were stimulated to contract at lower potassium concentrations than were myenteric muscles. Contractions of submucosal muscles at each potassium concentration studied were more forceful than contractions of myenteric muscles. Plots of membrane potential vs. potassium concentration on a logarithmic scale showed that the membrane potential of myenteric cells was more dependent upon the potassium gradient than the membrane potential of submucosal cells. The potassium permeability of both groups of cells increased when depolarized, and the slopes of these plots approached Nernstian levels when depolarized below -55 mV. Force developed in submucosal strips at more polarized levels than in myenteric muscles. The 'mechanical threshold' of submucosal muscles was 5-10 mV above resting potential, whereas myenteric muscles had to be depolarized by 25-30 mV before contraction was initiated. The mechanisms responsible for the difference in mechanical thresholds are not known, but differences in the voltage dependence of calcium channels, in calcium release mechanisms, or in the sensitivity of the contractile proteins to calcium could be involved.

Animals↗

PubMed1985

Erosive arthritis in Cronkhite-Canada syndrome.

A patient with Cronkhite-Canada syndrome and an erosive arthritis whose course correlated with the activity of his bowel disease is described. We found no previous description of articular manifestations in any patients with this syndrome. Cronkhite-Canada syndrome should be added to the differential diagnosis of erosive arthritis in the appropriate clinical setting.

Aged↗

PubMed1985

Myogenic regulation of propagation in gastric smooth muscle.

Experiments were performed to test the effects of frequency and stretch on the velocity of slow wave propagation parallel and perpendicular to the long axis of circular muscle fibers in the canine gastric antrum. Slow waves were evoked from one corner of a rectangular sheet of muscle and propagated throughout the tissue. Mathematics were derived and are presented, which simultaneously compute conduction velocities in each direction, regardless of electrode positions. Increased rate of stimulation had no significant effect on conduction velocity in the circumferential axis, but propagation slowed in the axis perpendicular to the circular fibers by an average of 25% over interstimulus intervals between 12 and 60 s. Conduction velocity was also a function of the degree of stretch. The most rapid conduction velocity occurred when muscles were stretched to an average of 118% of the resting, fasted length found in situ in the axis parallel to the circular fibers and 140% in the axis perpendicular to the circular fibers. Propagation was blocked by stretching muscles past 200% of resting length. These results suggest that the frequency of slow waves and gastric distension are intrinsic mechanisms capable of regulating the spread of slow waves.

Animals↗