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Excitatory and inhibitory enteric neural input to intestinal muscle acting on ongoing myogenic activity determines the rich repertoire of motor patterns involved in digestive function. The enteric neural activity cannot yet be established during movement of intact intestine in vivo or in vitro. We propose the hypothesis that is possible to deduce indirectly, but reliably, the state of activation of the enteric neural input to the muscle from measurements of the mechanical state of the intestinal muscle. The fundamental biomechanical model on which our hypothesis is based is the ‘three-element model’ proposed by Hill. Our strategy is based on simultaneous video recording of changes in diameters and intraluminal pressure with a fibre-optic manometry in isolated segments of rabbit colon. We created a composite spatiotemporal map (DPMap) from diameter (DMap) and pressure changes (PMaps). In this composite map rhythmic myogenic motor patterns can readily be distinguished from the distension induced neural peristaltic contractions. Plotting the diameter changes against corresponding pressure changes at each location of the segment, generates ‘orbits’ that represent the state of the muscle according to its ability to contract or relax actively or undergoing passive changes. With a software developed in MatLab, we identified twelve possible discrete mechanical states and plotted them showing where the intestine actively contracted and relaxed isometrically, auxotonically or isotonically, as well as where passive changes occurred or was quiescent. Clustering all discrete active contractions and relaxations states generated for the first time a spatio-temporal map of where enteric excitatory and inhibitory neural input to the muscle occurs during physiological movements. Recording internal diameter by an impedance probe proved equivalent to measuring external diameter, making possible to further develop similar strategy in vivo and humans.

Excitatory and inhibitory enteric neural input to intestinal muscle acting on ongoing myogenic activity determines the rich repertoire of motor patterns involved in digestive function. The enteric neural activity cannot yet be established during movement of intact intestine in vivo or in vitro. We propose the hypothesis that is possible to deduce indirectly, but reliably, the state of activation of the enteric neural input to the muscle from measurements of the mechanical state of the intestinal muscle. The fundamental biomechanical model on which our hypothesis is based is the "three-element model" proposed by Hill. Our strategy is based on simultaneous video recording of changes in diameters and intraluminal pressure with a fiber-optic manometry in isolated segments of rabbit colon. We created a composite spatiotemporal map (DPMap) from diameter (DMap) and pressure changes (PMaps). In this composite map rhythmic myogenic motor patterns can readily be distinguished from the distension induced neural peristaltic contractions. Plotting the diameter changes against corresponding pressure changes at each location of the segment, generates "orbits" that represent the state of the muscle according to its ability to contract or relax actively or undergoing passive changes. With a software developed in MatLab, we identified twelve possible discrete mechanical states and plotted them showing where the intestine actively contracted and relaxed isometrically, auxotonically or isotonically, as well as where passive changes occurred or was quiescent. Clustering all discrete active contractions and relaxations states generated for the first time a spatio-temporal map of where enteric excitatory and inhibitory neural input to the muscle occurs during physiological movements. Recording internal diameter by an impedance probe proved equivalent to measuring external diameter, making possible to further develop similar strategy in vivo and humans. [ABSTRACT FROM AUTHOR]

Purpose. Three new computational strategies have been evaluated for their ability to predict intestinal membrane permeability to a series of endothelin receptor antagonists. Methods. The three methods were evaluated using a set of ten non-peptide endothelin receptor antagonists. The simplest method, 'the rule of five', is based on 2D parameters such as the number of potential hydrogen bonds, molecular weight and calculated lipophilicity. A method based on molecular mechanics calculations is used to calculate 3D parameters such as polar and non-polar parts of the molecular surface area. The third method uses quantum mechanics to calculate molecular properties related to the valence region. Results. Descriptors derived by the latter two methods correlated well with permeability coefficients of the endothelin receptor antagonists. On the other hand, the rule of five failed to discriminate between drugs with high and low permeability. Conclusions. Molecular surface descriptors and descriptors derived from quantum mechanics are potentially useful for the virtual screening of the permeability of the intestinal membrane to endothelin receptor antagonists. [ABSTRACT FROM AUTHOR]

A highly enriched preparation of basolateral membrane vesicles was isolated from rabbit distal colon surface epithelial cells employing the method described by Wiener, Turnheim and van Os (Weiner, H., Turnheim, K., van Os, C.H. (1989) J. Membrane Biol. 110:147-162) and incorporated into planar lipid bilayers. With very few exceptions, the channel activity observed was that of a high conductance. Ca2+-activated K+ channel. This channel is highly selective for K+ over Na+ and Cl-, displays voltage-gating similar to "maxi" K(Ca) channels found in other cell membranes, and kinetic analyses are consistent with the notion that K+ diffusion through the channel involves either the binding of a single K+ ion to a site within the channel or "single-filing" ("multi-ion occupancy"). Channel activity is inhibited by the venom from the scorpion Leiurus quinquestriatus, Ba2+, quinine, and trifluoperazine. The possible role of this channel in the function of these cells is discussed. [ABSTRACT FROM AUTHOR]

The effects of the addition of graded concentrations of amiloride, (A)m, to the mucosal bathing solution on the permeability of the apical membrane of rabbit descending colon to Na (PmNa) were determined when the Na activity in the mucosal bathing solution, (Na)m, was 18, 32 or 100 mM. PmNa was obtained from current-voltage relations determined on tissues bathed with a high-K serosal solution before and after the addition of a maximally inhibitory concentration of amiloride to the mucosal solution as described by Turnheim et al. (Turnheim, K., Thompson, S.M., Schultz, S.G. 1983. J. Membrane Biol. 76:299-309). The results indicate that: (1) As demonstrated previously (Turnheim et al., 1983), PmNa decreases with increasing (Na)m. (2) PmNa also decreases hyperbolically with increasing (A)m. Kinetic analyses of the effect of amiloride on PmNa are consistent with the conclusions that: (i) the stoichiometry between the interaction of amiloride with apical membrane receptors that results in a decrease in PmNa is one-for-one; (ii) there is no evidence for cooperativity between amiloride and these binding sites; (iii) the value of (A)m needed to halve PmNa at a fixed (Na)m is 0.6-1.0 microM; and, (iv) this value is independent of (Na)m over the fivefold range studied. These findings are consistent with the notion that the sites with which amiloride interacts to bring about closure of the channels through which Na crosses the apical membrane are kinetically distinct from the sites with which (Na)m interacts to bring about closure (i.e., "self-inhibition"). In short, the effects of (Na)m and (A)m on PmNa in this tissue appear to be independent and additive. [ABSTRACT FROM AUTHOR]

H-Ouabain binding to isolated epithelia and basolateral membrane vesicles of Na-transporting epithelial cells of rabbit descending colon was determined to quantify the number of operative Na-pump sites at different rates of transcellular Na transport which was varied over a wide range by chronic dietary Na restriction or Na loading. Both in intact epithelia and in basolateral membrane vesicles the maximal number of specific ouabain binding sites was higher in preparations from animals transporting Na at high rates than in preparations from animals transporting Na at low rates. The affinity of ouabain to its binding site and the association and dissociation rate constants were not dependent on the rate of Na transport. In intact epithelia the Na turnover rate per pump unit was twice as high in tissues with high Na transport than in tissues with low Na transport. In basolateral membrane vesicles the Na turnover rate was considerably higher than in intact epithelia and there was no difference in turnover rate between vesicle preparations obtained from tissues transporting Na at high or low rates. Hence, factors within the intact cell appear to control the turnover rate of the Na-pump. [ABSTRACT FROM AUTHOR]

The relation between intracellular Na activities, (Na), determined employing Na-selective microelectrodes, and the rates of active Na absorption, I, by rabbit descending colon was examined when I was varied over a wide range by chronic dietary Na deprivation. (Na) averaged 13 mM and was independent of I over a sixfold range. Further, the ratios of the slope resistance of the apical membrane ( r) to that of the basolateral membrane ( r) (i.e. r/ r) in low-transporters (control diet) and high-transporters (Na-deprived) did not differ significantly inspite of the fact that the Na conductance of the apical membranes of high-transporters was, on the average, three times greater than that of the low-transporters. These findings, together with the results reported by other laboratories, strongly suggest that the aldosterone-induced increase in the conductance of the apical membrane to Na and, in turn, the rate of entry of Na into the absorptive cells are followed by parallel increases in the ability of cells to extrude Na across the basolateral membrane in the absence of a sustained increase in (Na) as well as the conductance of that barrier. [ABSTRACT FROM AUTHOR]

The effects of the diuretic drug ozolinone on electrogenic Cl secretion by rabbit colonic mucosa were investigated in vitro. Electrical properties and unidirectional Cl fluxes were measured in stripped preparations mounted in Ussing-type chambers. After abolition of electrogenic Na absorption by amiloride (10 mol/l) on the mucosal side electrogenic Cl secretion was induced by addition of PGE (10mol/l, serosal side) and theophylline (10mol/l, both sides). Under these conditions, the monitored short-circuit current (I) equals the amount of Cl secreted as evidenced by determination of unidirectional Cl fluxes. After establishing a stable Cl secretion its sensitivity to the enantiomers of the diuretic was studied. Only levorotatory (-)-ozolinone, but not the dextrorotatory (+)form, inhibited Cl secretion on serosal application. This effect was fully accounted for by a reduction in the serosal-to-mucosal Cl fluxes (J). It was readily reversible and concentration-dependent with a K value of 6×10mol/l, but absent when the drug was added to the mucosal side. The results are in agreement with the hypothesis that loop diuretics inhibit a coupled NaCl entry mechanism across the baso-lateral membrane into colonic epithelial cells. This mechanism is though to account for Cl influx into the cells. [ABSTRACT FROM AUTHOR]