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S M Thompson

Publications and source records attributed to S M Thompson.

At least 109 records · Page 6Linked to original sources
PubMed1983

Dentin permeability: effects of temperature on hydraulic conductance.

The rates of fluid movement across dentin discs, in vitro, were measured at 10, 20, 30, 40, and 50 degrees C in unetched and acid-etched dentin. Increasing the temperature 40 degrees (i.e., from 10 to 50 degrees C) resulted in a 1.8-fold increase in fluid flow in unetched dentin, which was of a magnitude similar to the decrease in viscosity that occurred over the same temperature range. In acid-etched dentin, the 40 degrees C temperature change produced more than a four-fold increase in fluid conductance, more than double that which could be accounted for by changes in viscosity. Analysis of the data suggests that this additional increment in hydraulic conductance is due to thermal expansion-induced increases in tubular diameter.

Acid Etching, Dental↗
PubMed1983

Should diabetes be a contraindication for an intraocular lens?

Twenty-five patients with Binkhorst 4-loop intraocular lenses were studied to assess the ease of visualization of their fundi, and the feasibility of treating diabetic retinopathy. All patients had fulfilled several pre-operative selection criteria. Visualization with the direct ophthalmoscope and posterior pole contact lens was good in most cases through undilated pupils. Documentation of fundus abnormalities by fundus photography and fluorescein angiography was possible only if the pupils were dilated. Retinal photocoagulation with argon laser could be carried out through the intraocular lenses in all patients requiring treatment. Iris clip lenses should not be regarded as contraindicated in selected diabetic patients.

Adult↗
PubMed1982

The electrophysiology of rabbit descending colon. II. Current-voltage relations of the apical membrane, the basolateral membrane, and the parallel pathways.

In this paper we employ the data described in the previous paper (I) to derive the current-voltage (I-V) relations of the basolateral membrane, the amiloride-insensitive "leak" pathway across the apical membrane, and the parallel pathways across rabbit descending colon. The results indicated that: a) The resistance of the basolateral membrane is independent of the electrical potential difference across that barrier over the range -8 to 67 mV and averaged 195 omega cm2. The electromotive force across this barrier averaged 50 mV under control conditions and 48 mV in the presence of amiloride. The origin of this difference is discussed. b) The resistance of the parallel pathways averaged 351 omegacm2 and was independent of the transepithelial electrical potential difference over the range -170 to + 90mV. The conductance of these pathways can be reasonably well accounted for by the partial ionic conductances of Na, K and Cl reported previously. c) The resistance of the amiloride-insensitive pathway across the apical membrane averaged 1667 omegacm2 and the electromotive force across this pathway averaged -51 mV. These values are in excellent agreement with those determined by others. The ionic nature of this "leak" pathway remains to be elucidated.

Amiloride↗
PubMed1982

A comparative study of EM fixation procedures for the adult rat spinal cord based on regional blood flow.

Adult rat spinal cords were perfused intracardially with aldehyde fixatives containing either sodium cacodylate or sodium phosphate buffer for EM studies. The perfusion flow rate of 24 cc/min for the first 3 min and 33 cc/min for completion of prefixation was found to be optimal. Ultrastructural examination of the L-1 fasciculus gracili, dorsal and ventral horns demonstrated that the quality of fixation is similar despite a two- to three-fold greater blood flow rate to the dorsal and ventral horns, respectively. Sodium cacodylate buffered perfusate provides superior clarity of organelle membranes, myelin lamellae and axoplasmic constituents when compared with sodium phosphate buffer.

Animals↗
PubMed1982

Double labelling of neuronal somata by [3H]uridine and horseradish peroxidase: a technique to demonstrate two-stage connections with the light microscope.

A new technique is described that may demonstrate two-stage connection at the light microscopic level. Anterograde transneuronal transport of [3H]uridine is used in conjunction with retrograde transport of horseradish peroxidase (HRP). The two compounds are injected separately into different brain regions. Under conditions of proper controls, neuron somata that are double labelled are interpreted as receiving an afferent projection from the region injected with [3H]uridine and sending an efferent projection to the region injected with HRP. Thus, the technique can demonstrate two-stage connections in the nervous system.

Animals↗
PubMed1982

Interpretation and use of electrical equivalent circuits in studies of epithelial tissues.

Whereas transepithelial and intracellular voltages continue to be measured in renal and other epithelial tissues, the origins of these voltages, especially in renal epithelia, remain obscure. Because epithelial tissues have multiple transcellular and extracellular routes of ion transport, it is convenient to model them with electrical equivalent circuits and, in this way, attempt to understand the relative importance of and relationships between the parallel-series arrangements of the membranes and barriers involved. The interpretation of the equivalent electromotive forces and resistances can be complicated, however, by virtue of nonlinear current-voltage relationships of ionic channels. Thus, for ion transport pathways displaying nonlinear I-V relationships, it is important to distinguish between chord and slope formalisms in the use and interpretation of electrophysiological data. For ions like Na that are generally not at electrochemical equilibrium, the Thévenin electromotive force (emf) of the slope formalism is not synonymous with the Nernst equilibrium potential of the chord formalism nor are the slope and chord conductances equal or constant at all voltages. Thus, it is mandatory that the empirical data be calculated and interpreted in a way consistent with the formalism adopted. The existence of nonlinear behavior, characterized by either Goldman or other types of rectification, exacerbates determination of relative ionic permeabilities, fractional resistances, transference numbers, and other electrophysiological parameters for simple membranes and especially for epithelia. It is argued that the use and interpretation of electrical equivalent circuits of epithelia are not arbitrary but must take into account nonlinearities of the ionic current-voltage relationships and concentration and voltage dependencies of the emfs and conductances.

Animals↗
PubMed1981

Equivalent electrical circuit models and the study of Na transport across epithelia: nonsteady-state current-voltage relations.

After successfully impaling an absorptive cell of rabbit colonic epithelium with a microelectrode, "instantaneous" transepithelial current-voltage relations were determined under control conditions and in the presence of a maximally effective dose of amiloride. The results are interpreted using a very general equivalent electrical circuit model that admits the presence of an apical membrane conductance(s) to an ion(s) other than Na as well as the possibility of an incomplete action of amiloride on the Na entry step. The derived relation between the instantaneous Na current across that barrier conforms closely to the predictions of a simple, charged carrier model. The "reversal potential" of 64 mV is consistent with an intracellular Na activity of 11 nM. Finally, some of the implications of these findings are discussed with respect to 1) the applicability of linear models of active transepithelial Na transport, and 2) the experimental determinations and meanings of the "overall electromotive force" (ENa) and the "overall resistance" (RNa) of active Na transport.

Amiloride↗
PubMed1979

Intracellular chloride activities and active chloride absorption in the intestinal epithelium of the winter flounder.

Intracellular chloride activities, (Cl)c, and the electrical potential difference across the mucosal membrane, psimc, were determined in the isolated small intestine of the winter flounder, using Cl-selective and conventional (KCl-filled) microelectrodes. In the presence of a Na-containing buffer psimc averages -69 mV and (Cl)c averages 24 mM, a value that is 3.4 times that predicted for an equilibrium distribution across the mucosal membrane. On the other hand, when the tissue is then perfused with Na-free buffer, (Cl)c slowly falls to a value that does not differ significantly from that predicted for an equilibrium distribution, and psimc depolarizes significantly. Finally, when the tissue is again bathed in the Na-containing buffer, (Cl)c rapidly returns to a value well above equilibrium. These results, together with those of Frizzell et al. (J. Membrane Biol. 46:27, 1979), provide direct evidence that: (1) Cl is accumulated against its electrochemical potential difference (32 mV) by this tissue, and (2) this accumulation is coupled to and energized by the entry of Na down its steep electrochemical potential difference.

Animals↗
PubMed1978

Sodium uptake across the apical border of the isolated turtle colon: confirmation of the two-barrier model.

The initial rate of Na uptake by the turtle colon from the mucosal bathing solution consists of two operationally distinct components. One component is a linear function of mucosal Na concentration, is unaffected by amiloride, and appears to represent Na uptake into the paracellular shunt path. The major component of Na uptake is abolished by amiloride and is virtually equal to the short-circuit current over a wide range of mucosal Na concentrations, suggesting that this portion of Na uptake represents Na movement into Na-transporting cells of the colon. The amiloride-sensitive component of Na uptake, at low mucosal Na concentrations, was unaffected if net Na transport was abolished by ouabain. Similarly, at low mucosal Na concentrations the amiloride-sensitive conductance of the colon was identical in the presence and in the absence of net Na transport. These results show that the isolated turtle colon behaves as two distinct barriers to transmural Na transport, an apical barrier blocked by amiloride and a more basal-lying barrier where active, transmural Na transport is blocked by ouabain. In addition, these experiments appear to provide the first unambiguous demonstration that the initial-rate isotope uptake technique can provide a direct measure of the properties of the amiloride-sensitive barrier to transmural Na movement, presumably the apical membranes of the Na-transporting cells. The results are consistent with the notion that the rate of transmural active Na transport and the conductance of the active Na-transport path are determined by the properties of the apical membrane.

Amiloride↗
PubMed1978

Cation selectivity of the apical membrane of the turtle colon: sodium entry in the presence of lithium.

Exposure of the apical surface of the isolated turtle colon to Li produced a marked transient in short-circuit current (ISC) and total tissue conductance (GT) which was abolished by amiloride but was unaffected by ouabain or by removing Na or Cl from the mucosal bathing solution. Despite marked changes in Isc, Na uptake across the apical membrane was a linear function of time during exposure to Li-containing solutions, and except at very high Li concentrations, the initial rate of Na uptake, JiNa, was identical to its pre-Li value. In the presence of Li, however, JiNa was significantly less than the total Isc. The apparent "transference number" for Na in the apical membranes was a function of the Li:Na concentration ratio in the mucosal bathing solution. These results suggest that Li can carry substantial amounts of current through amiloride-sensitive channels in the apical membrane of the colon without having any effect on the rate coefficient for Na entry. This behavior is not consistent with "competition" of Na and Li for a membrane "carrier" but rather suggests that the Na entry mechanism may be a population of pores or channels through which Na and Li may pass with negligible interaction.

Amiloride↗
PubMed1978

A study of the influence of the method of oral administration of ampicillin upon plasma drug levels in calves.

Ampicillin was given orally to five Holstein calves using the following four different methods of administration: via stomach tube, mixed and fed in the calf starter ration, dissolved in milk and pail fed and administered orally as 400 mg commercial calf tablets. In addition, ampicillin was dissolved in milk and pail fed 20 to 30 minutes following intramuscular atropine. Ampicillin was only detected in the plasma of calves which had received the drug, pail fed in milk. Atropine administration slowed the appearance of the drug in the plasma but did not decrease the efficiency of absorption.

Administration, Oral↗