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PubMed1981

[Electrophysiologic demonstration of dual atrioventricular nodal pathways and final common pathway in a case of A-V nodal paroxysmal tachycardia. Considerations on the functional complexity of the A-V node (author's transl)].

The AA. studied the A-V nodal conduction using the technique of induced PAB in a patient with A-V reentrant paroxysmal tachycardia. They observed that the conduction through the A-V node failed when coupling intervals A1-A2 were between 280 and 260 msec and, after, recovered, with consistent slackening, when A1-A2 intervals were shortened, until the atrial ERP was reached. This uncommon response indicates the functional complexity of the A-V node and, particularly, suggests the presence of a final common pathway distal to the fast and slow A-V pathways, that are the anatomic-functional basis of the reentry circuit in A-V nodal paroxismal tachycardia.

Atrioventricular Node↗
PubMed1975

Energy metabolism of spermatozoa. V. The Embden-Myerhof pathway of glycolysis: activities of pathway enzymes in hypotonically treated rabbit epididymal spermatozoa.

Seven enzymes of the Embden-Myerhof pathway of glycolysis were assayed in hypotonically treated epididymal sperm from mature rabbits. These were: fructose-biphosphate aldolase, triosephosphate isomerase, glyceraldehydephosphate dehydrogenase, 3-phosphoglyceromutase, enolase, pyruvate kinase, and lactate dehydrogenase. These enzymes were firmly enough bound to the cell structure to resist removal by washing after hypotonic treatment and had maximal activities comparable to, or greater than, the rate of mitochondrial pyruvate oxidation, so that rapid oxygen uptake was observed with intermediates of the glycolytic pathway. The activity of lactate dehydrogenase in a typical preparation of hypotonically treated cells was 5.3 mumoles/minute x 10(9) cells at 25 degrees C for pyruvate reduction in the hypotonically treated cells and 4.8 mumoles/minute x 10(9) cells in the thrice-washed hypotonically treated cells. The Km for pyruvate was 1.4 mM while that for lactate was 4.4 mM. By contrast, the maximal activity of pyruvate oxidation by mitochondria was 0.10 microgram atom of oxygen/minute x 10(9) cells, corresponding to 0.020 mumole of pyruvate/minute x 10(9) cells, and the Km for pyruvate was 5 microM. These enzyme parameters favor high lactate production from glucose in aerobic glycolysis.

Animals↗
PubMed1988

Auditory pathways in the budgerigar. II. Intratelencephalic pathways.

The projections of two telencephalic areas in receipt of projections from the auditory relay nucleus of the thalamus (nucleus ovoidalis) were studied in the budgerigar (Melopsittacus undulatus) with autoradiographic methods. These nuclei are called field 'L' and neostriatum intermedium pars dorsolateralis (NIDL). The results show that neurons in both fields project laterally to a portion of the neostriatum intermedium pars ventrolateralis (NIVL) and rostrally to the rostromedial archistriatum. Horseradish peroxidase experiments confirm these projections and indicate that field 'L', NIDL and NIVL also receive projections from neurons in the hyperstriatum ventrale (HV). The projections of field 'L' and NIDL neurons to the rostromedial archistriatum may act as pathways subserving auditory feedback. Neurons in this portion of the archistriatum project to the contralateral field 'L', NIDL and NIVL. Furthermore, the medial archistriatal projection field of neurons within field 'L', NIDL and NIVL (i.e. rostromedial archistriatum) is located adjacent to a large archistriatal neuronal field projecting to the medulla, including the lateral reticular formation of the medulla. This large archistriatal field includes the nucleus archistriatalis robustus, the telencephalic nucleus identified as the source of projections to the lower motoneurons of the syrinx. Thus, projections from auditory telencephalic areas to the rostromedial archistriatum may serve functions related to processes associated with learning and vocal motor control.

Animals↗
PubMed1995

Caudal medullary pathways to lumbosacral motoneuronal cell groups in the cat: evidence for direct projections possibly representing the final common pathway for lordosis.

The nucleus retroambiguus (NRA) projects to distinct brainstem and cervical and thoracic cord motoneuronal cell groups. The present paper describes NRA projections to distinct motoneuronal cell groups in the lumbar enlargement. Lumbosacral injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) were made to localize and quantify the retrogradely labeled neurons in the caudal medullary lateral tegmentum. These injections were combined with spinal hemisections to distinguish between neurons having ipsi-or contralaterally descending axons. The NRA-lumbosacral fibers descend almost exclusively contralaterally, but neurons in areas surrounding the NRA project mainly ipsilaterally. In an anterograde tracing study, injections of WGA-HRP or tritiated leucine were made in the region of the NRA to determine the NRA targets in the lumbosarcral cord. Hemisections in C2 made it possible to distinguish between NRA projections and projections from neurons in the adjoining lateral tegmentum. The results show delicate NRA projections to distinct lumbosacral motoneuronal cell groups innervating specific hindlimb muscles (iliopsoas, adductors, and hamstrings) as well as axial muscles (medial longissimus and proximal tail muscles). The projection is bilateral, with a contralateral predominance. Ipsilaterally terminating fibers are derived from NRA neurons whose axons cross the midline at the level of the obex, descend through the contralateral spinal white matter, and recross at the level of termination. A conceptual description is presented in which the periaqueductal gray-NRA-lumbosacral projections form the final common pathway for lordosis in the cat.

Animals↗
PubMed1989

The organization of descending tectofugal pathways underlying orienting in the frog, Rana pipiens. II. Evidence for the involvement of a tecto-tegmento-spinal pathway.

In the frog, identical orienting deficits, involving a failure to turn toward stimuli in the ipsilateral hemifield, can be produced by small white matter lesions either in the caudal mesencephalon (Kostyk and Grobstein, 1987a) or in the caudal medulla (Masino and Grobstein, 1989). These findings suggest that descending turn signals may run uninterrupted from the midbrain to the spinal cord, and that something other than tectospinal axons may carry such signals. We here report studies to determine whether there is a tecto-recipient structure whose axons pass through the known critical lesion sites in the caudal mesencephalon and medulla, and whether damage to such a structure, sparing tectospinal pathways, produces an orienting deficit. Horseradish peroxidase (HRP) was applied to behaviorally effective lesions in the caudal medulla and the resulting labelling patterns compared with those resulting from application of HRP to nearby but behaviorally ineffective lesions at the same rostrocaudal level. A column of large cells in the ventrolateral midbrain tegmentum (including nMLF as well as parts of AV and PV) was robustly labelled in all effective lesion cases, and less frequently labelled in ineffective cases. A quantitative analysis showed labelling in this region to be more highly correlated with the existence of a behavioral deficit than that in any other brain region. Reconstructions of single retrogradely labelled cells in the rostral part of the column (nMLF) showed that they have dendrites in a position to receive tectal input and axons which pass through the critical lesion sites in both the caudal mesencephalon and the caudal medulla. Tegmental lesions, sparing the tectospinal tracts, produced ipsilateral turning deficits in cases where the large cell column was completely removed but did not when the column was spared. The findings support the hypothesis that tectofugal signals involved in orienting turns descend uninterrupted to the spinal cord on something other than tectospinal axons, and suggest that the critical projections derive from the large cell column of the ventral tegmentum.

Animals↗
PubMed1984

A [14C]2-deoxyglucose analysis of the functional neural pathways of the limbic forebrain in the rat. IV. A pathway from the prefrontal cortical-medial thalamic system to the hypothalamus.

The present study utilized the [14C]2-deoxyglucose (2-DG) cell labeling procedure to characterize a functional pathway from the prefrontal cortex (Pfc) and mediodorsal thalamic nucleus (MD) to the hypothalamus. Rats were injected with 2-DG prior to a 45 min experimental paradigm consisting of alternating 30 s on-off periods of electrical brain stimulation. Standard procedures were utilized for the removal and processing of brain tissue for X-ray autoradiography. In the first phase of this study, stimulation applied to the prefrontal cortex generally yielded a pattern of 2-DG distribution consistent with the findings of classical anatomical studies. Stimulation of the dorsomedial and ventromedial prefrontal cortex or the infralimbic cortex produced the most effective activation of the diencephalon. This activation was primarily limited to MD, with no involvement of any region of the hypothalamus. In the second phase of this study, brain regions activated following stimulation of sites along the rostro-caudal axis of MD were examined. Stimulation of MD resulted in the activation of the nucleus reuniens and other midline and non-specific thalamic nuclei. Stimulation of this nucleus also activated the ventromedial thalamic nucleus, medial aspects of the nucleus accumbens and the medial and sulcal prefrontal cortices. Again, in each of these cases, labeling within any region of the hypothalamus could not be detected. Since MD stimulation activated the midline thalamus, and the nucleus reuniens in particular, the last phase of this experiment involved stimulation of the nucleus reuniens in order to determine the source of medial thalamic inputs to the hypothalamus. Stimulation of the nucleus reuniens activated fibers which were distributed to both the medial and lateral hypothalamus. In addition, stimulation also activated the descending periventricular system, which could be followed to the level of the midbrain central gray and such limbic structures as the hippocampal formation, septal area, amygdala and prefrontal cortex. These findings indicate that Pfc-MD activation of the hypothalamus is achieved indirectly via interneurons within the nucleus reuniens.

Animals↗
PubMed1988

Regulation of pathways of glucose metabolism in the kidney. The activity of the pentose phosphate pathway, glycolytic route and the regulation of phosphofructokinase in the kidney of lean and genetically obese (ob/ob) mice; comparison with effects of diabetes.

The activities of enzymes of the glycolytic route, the pentose phosphate pathway and NADPH-linked enzymes have been measured in the kidneys of genetically obese (ob/ob) mice and their lean litter mates. The renal content of glucose 6-phosphate (G6P), fructose 6-phosphate (F6P), fructose 1,6-bisphosphate (Fru-1,6-P2) and fructose 2,6-bisphosphate (Fru-2,6-P2) were also measured. Increases were found in hexokinase and enolase with an upward trend in pyruvate kinase in the ob/ob mouse kidney; a significant decline in malic enzyme was also seen. The renal content of G6P and Fru-1,6-P2 increased. There was no renal hypertrophy despite a degree of hyperglycaemia, which was, however, considerably below that observed in experimental diabetes. Comparison of the renal changes in the hyperglycaemic-hyperinsulinaemic ob/ob mice with the hyperglycaemic-hypoinsulinaemic diabetic group showed two distinct groupings. Firstly, changes which were similar in the two groups included: increases in hexokinase, G6P and Fru-1,6-P2, and a decrease in malic enzyme. Secondly, opposite changes were seen in enolase and in enzymes at the G6P crossroads, phosphoglucose isomerase and phosphoglucomutase. The elevated hexokinase and G6P in both ob/ob and diabetic groups may be involved in the eventual accumulation of basement membrane material in the glomerulus which is a common feature of the two conditions.

Animals↗
PubMed1981

The role of immunoglobulins in alternative complement pathway activation by zymosan. I. Human IgG with specificity for Zymosan enhances alternative pathway activation by zymosan.

Prior absorption of normal human serum (NHS) or C2-deficient human serum (C2D) with zymosan at 0 degrees C results in diminished consumption of C3 and factor B during subsequent incubation of the sera in Mg-EGTA buffer with zymosan at 37 degrees C for 30 min. An acid eluate from the zymosan restores the defect of absorbed NHS and C2D, and also enhances C3 and factor B utilization in hypogammaglobulinemic serum (H gamma S) in a dose-dependent fashion. The activity is specific in that the eluate from zymosan fails to enhance C3 and B depletion in H gamma S or absorbed NHS by lipopolysaccharide or Sepharose. The active component of th zymosan eluate emerges from both Sepharose 4B and Sephacryl S-200 in the region of molecules with m.w. of 150,000. Absorption with protein A-Sepharose removes the activity, demonstrating that it is IgG. Digestion of the IgG with pepsin fails to diminish activity, indicating that the Fc region is not required for activity; reduction to monovalent Fab' fragments, however, abrogates activity. When IgG antibody is bound to Protein A-Sepharose, it fails to enhance C3 depletion in H gamma S by Sepharose, indicating that binding of IgG antibody by the Fab region is necessary for enhancement of alternative pathway activity in human serum.

Antibody Specificity↗
PubMed1983

Spatial relationships between the terminations of somatic sensory motor pathways in the rostral brainstem of cats and monkeys. II. Cerebellar projections compared with those of the ascending somatic sensory pathways in lateral diencephalon.

Previous studies have shown that ascending somatic sensory pathways arising from the dorsal column nuclei, lateral cervical nucleus and spinothalamic tract terminate in parts of the thalamus adjacent to those which receive cerebellar terminations. This termination pattern creates a border between the ventroposterolateral nucleus (VPL) and the ventrolateral nucleus (VL) in the cat and between the caudal and oral parts of VPL (VPLc and VPLo, respectively) in the monkey. Since it is not clear how sharp these borders are, a double orthograde labeling strategy was used in the present study to make direct comparisons of the projections to the thalamus from these sources of input. It was found that there was a change in the sources of afferent input to the different target areas that paralleled changes in cytoarchitecture. Moving caudally to rostrally, VPL in the cat and VPLc in the monkey received projections predominantly from the middle, dorsal (clusters) portion of the dorsal column nuclei. These projections were gradually replaced near the VPL-VL border in the cat and VPLc-VPLo border in the monkey first by input from the lateral cervical nucleus (cat only) and the rostral and ventral portions of the dorsal column nuclei and then by spinothalamic projections. Towards VL in the cat and the rostral parts of VPLo in the monkey (referred to as Vim by Hassler, '59 and Mehler, '71), these projections were in turn replaced by those from the cerebellum. This sequence resulted in a complex pattern (summarized in Fig. 10) where some thalamic territories received input predominantly from one source and others received converging input from several sources. The major region receiving converging ascending somatic sensory and cerebellar terminations was located at the border between VPL and VL in the cat and in the caudal parts of Olszewski's ('52) VPLo in the monkey (that is, between VPLc and Vim). In general, the results in the cat were similar to those in the monkey. One notable difference was that the domain containing terminals from the cerebellum and the rostral-ventral parts of the dorsal column nuclei was located medially between VPLc and Vim in the monkey, whereas it extended across the entire mediolateral border between VPL and VL in the cat. In both species, thalamic neurons received input predominantly from one afferent source and only minor input, if any, from other sources.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Primate spinothalamic pathways: II. The cells of origin of the dorsolateral and ventral spinothalamic pathways.

The cells of origin of the dorsolateral (DSTT) and the ventral (VSTT) spinothalamic tracts were studied in 11 monkeys. The spinothalamic tract cells were retrogradely labeled by horseradish peroxidase (HRP) injected in the thalamus. All animals also received a midthoracic spinal cord lesion on the side ipsilateral to the thalamic injections. The distribution of labeled cells found in these animals throughout the cervical segments was similar to animals with no spinal cord lesions. Five animals had ventral quadrant lesions to demonstrate the cells of origin of the DSTT. In macaques with complete ventral quadrant lesions, more than 80% of the HRP label in the contralateral L4-L7 segments was located in lamina I, while in squirrel monkeys, the label in the contralateral lower lumbar region was distributed between laminae I-III and IV-VI. Few labeled cells were found in laminae VII-X. Six animals received dorsolateral funiculus lesions to demonstrate the cells of origin of the VSTT. In animals with adequate lesions, 84-99% of the contralateral HRP label in L4-L7 was located in laminae IV-X. Macaques had a larger percentage of labeled cells located in lamina I than squirrel monkeys. The results indicate the existence of two spinothalamic pathways in the primate. The DSTT was calculated to compose about one fourth of the total spinothalamic population.

Animals↗
PubMed1989

Primate spinothalamic pathways: III. Thalamic terminations of the dorsolateral and ventral spinothalamic pathways.

The termination sites of the dorsolateral (DSTT) and ventral (VSTT) spinothalamic pathways were determined by using anterograde transport of horseradish peroxidase from the lumbar spinal cord in primates. One animal had no spinal cord lesion, while of two other animals, one received a midthoracic dorsolateral funiculus lesion, and the other received a midthoracic ventral quadrant lesion contralateral to the injection. The thalamic label in the animal with no spinal cord lesion was much less than the label in the two animals with spinal lesions. Moreover, in the animals with spinal lesions, HRP-labeled cells were found within the thalamus. Therefore, the remaining six animals received ipsilateral hemisections and bilateral dorsal column lesions, irrespective of the contralateral lesions. The thalamic label in the animals without contralateral lesions were assumed to represent the total spinothalamic input to the diencephalon. In these animals, label was located mainly in suprageniculate and pulvinar oralis, caudal and oral divisions of ventral posterior lateral nucleus, the lateral half of ventral posterior inferior nucleus, and zona incerta, while in the medial thalamus label was primarily in two distinct bands in medial dorsal nucleus and in the posterior dorsal portion of central lateral nucleus. Scattered lighter labeling was found in other thalamic nuclei. The pattern of terminal labeling observed in the ventral posterior lateral region was arranged in patches, while elsewhere in the thalamus a more uniform labeling pattern was observed. The thalamic label in animals with contralateral ventral quadrant lesions represented the terminations of the DSTT, while the label in animals with contralateral dorsolateral funiculus lesions represented VSTT terminations. The labeling pattern was similar between these two groups. However, there were small differences between them. These results indicate that DSTT and VSTT terminations largely overlap and innervate the lateral and medial thalamamus.

Animals↗
PubMed1984

Regulation of alternative pathways of glucose metabolism in rat heart in alloxan diabetes: changes in the pentose phosphate pathway.

The flux of glucose through the pentose phosphate pathway, important in relation to the provision of ribose 5-phosphate for nucleotide and RNA synthesis, was decreased by 70% in the diabetic rat heart in parallel with a similar decreased flux through the glycolytic route. A common factor linking the decreased flux through these alternative routes is the known fall in cardiac hexokinase; in these experiments there is a 50% decrease in Type II hexokinase (EC 2.7.1.1.) in both soluble and particulate fractions. The level of fructose 2,6-bisphosphate, a regulator of phosphofructokinase activity, is decreased by 20% in the alloxan diabetic rat heart, this may be a significant additional factor in the marked decrease in the flux of glucose through the glycolytic route in the myocardium in diabetes.

Animals↗
PubMed1986

Do rat hepatic microsomes contain multiple NADPH-supported fatty acid chain elongation pathways or a single pathway?

[2-14C]-trans-2-hexadecenoyl CoA (16:1) and [2-14C]-trans-2-cis-8,11,14-eicosatetraenoyl CoA (20:4) were chemically synthesized and employed as competitive substrates for the liver microsomal trans-2-enoyl CoA reductase component of the fatty acid chain elongation system. Both 7.5 microM and 15 microM 20:4 competitively inhibited the reduction of 16:1 CoA to palmitoyl CoA. In addition, the reduction of both substrates was identically inhibited to the same extent by the acetylenic derivative, dec-2-ynoyl CoA. Furthermore, trypsin, chymotrypsin and subtilisin inhibited trans-2-enoyl CoA reductase activity when three different substrates were employed--16:1, 20:4 and trans-2-cis-11-octadecadienoyl CoA (18:2). These results are consistent with the hypothesis of multiple condensing enzymes connected to a single elongation pathway.

Acyl-CoA Dehydrogenases↗
PubMed1983

Embryogenesis of peripheral nerve pathways in grasshopper legs. I. The initial nerve pathway to the CNS.

The founding of the first nerve path of the grasshopper metathoracic leg was examined at the level of identified neurons, using intracellular dye fills, immunohistochemistry, Nomarski optics, and scanning and transmission electron microscopy. The embryonic nerve is established by the axonal trajectory of a pair of afferent pioneer neurons, the tibial 1 (Ti1) cells. Following a period of profuse filopodial sprouting, the Ti1 axonal growth cones, possessing 75- to 100-microns-long filopodia, navigate a stereotyped path across the limb bud epithelium to the base of the appendage and into the CNS. The Ti1 axons grow from cell to cell along a chain of preaxonogenesis neurons spaced at intervals along the pathway, forming dye-passing junctions with them. The contacted neurons subsequently undergo axonogenesis and follow the pioneer axons into the CNS. Later arising neurons project their axons onto the cell bodies of the chain, thereby establishing the principal branch points of the nerve. Among the later arising afferents are the sensory neurons of the femoral chordotonal and subgenual organs. The morphology of the adult nerve appears to be determined by the stereotyped positioning of neurons in the differentiating limb bud and by the resultant axonal trajectories established during the first 10% of peripheral neurogenesis.

Animals↗
PubMed1991

Ultracytochemistry of the secretory pathway in Saccharomyces cerevisiae defies the established pathway model.

The molecular and cell biologic data supporting the established model of the intracellular secretory (transport) pathway for glycoproteins in the yeast Saccharomyces cerevisiae have been reviewed and confronted with our electron-cytochemical findings. These in situ findings show a new class of constitutive intracellular conveyors--the coated globules--and also suggest substantial alternatives in the cellular mechanism of the vacuole biogenesis. The controversial question of the Golgi compartment identity in S. cerevisiae is revived.

Dipeptidyl-Peptidases and Tripeptidyl-Peptidases↗
PubMed1990

Chemical pathways of peptide degradation. III. Effect of primary sequence on the pathways of deamidation of asparaginyl residues in hexapeptides.

Deamidation of Asn residues can occur either by direct hydrolysis of the Asn residue or via a cyclic imide intermediate. The effects of primary sequence on the pathways of deamidation of Asn residues were studied using Val-Tyr-X-Asn-Y-Ala hexapeptides with substitution on the C-terminal side (Y) and on the N-terminal side (X) of the Asn residue. In acidic media the peptides deamidate by direct hydrolysis of the Asn residue to yield only Asp peptides, whereas under neutral or alkaline conditions, the peptides deamidate by formation of the cyclic imide intermediates which hydrolyze to yield both isoAsp and Asp peptides. At neutral to alkaline pH's the rate of deamidation was significantly affected by the size of the amino acid on the C-terminal side of the Asn residue. The amino acid on the C-terminal side of the Asn residue has no effect on the rate of deamidation at acidic pH. Changes in the structure of the amino acid on the N-terminal side of the Asn residue had no significant effect on the rate of deamidation at all the pH's studied. For peptides that underwent deamidation slowly, a reaction involving the attack of the Asn side chain on the peptide carbonyl carbon resulting in peptide bond cleavage was also observed.

Amino Acid Sequence↗
PubMed1991

Multiple pathways in nuclear transport: the import of U2 snRNP occurs by a novel kinetic pathway.

Protein import to the nucleus is a signal-mediated process that exhibits saturation kinetics. We investigated whether signal bearing proteins compete with U2 and U6 snRNPs during import. When injected into Xenopus oocytes, saturating concentrations of P(Lys)-BSA, a protein bearing multiple nuclear localization signals from SV40 large T-antigen, reduce the rate of [125I]P(Lys)-BSA and of [125I]nucleoplasmin import, consistent with their competing for and sharing the same limiting component of the import apparatus. In contrast, saturating concentrations of P(Lys)-BSA do not reduce the rate of HeLa [32P]U2 snRNP assembly or import. The import of U6 snRNP is also competed by P(Lys)-BSA. We conclude that U2 snRNP is imported into oocyte nuclei by a kinetic pathway that is distinct from the one followed by P(Lys)-BSA, nucleoplasmin, and U6 snRNP.

Animals↗
PubMed1986

Ionic conductance pathways in the mouse medullary thick ascending limb of Henle. The paracellular pathway and electrogenic Cl- absorption.

Net Cl- absorption in the mouse medullary thick ascending limb of Henle (mTALH) involves a furosemide-sensitive Na+:K+:2 Cl- apical membrane symport mechanism for salt entry into cells, which occurs in parallel with a Ba++-sensitive apical K+ conductance. The present studies, using the in vitro microperfused mouse mTALH, assessed the concentration dependence of blockade of this apical membrane K+-conductive pathway by Ba++ to provide estimates of the magnitudes of the transcellular (Gc) and paracellular (Gs) electrical conductances (millisiemens per square centimeter). These studies also evaluated the effects of luminal hypertonicity produced by urea on the paracellular electrical conductance, the electrical Na+/Cl- permselectivity ratio, and the morphology of in vitro mTALH segments exposed to peritubular antidiuretic hormone (ADH). Increasing luminal Ba++ concentrations, in the absence of luminal K+, produced a progressive reduction in the transcellular conductance that was maximal at 20 mM Ba++. The Ba++-sensitive transcellular conductance in the presence of ADH was 61.8 +/- 1.7 mS/cm2, or approximately 65% of the total transepithelial conductance. In phenomenological terms, the luminal Ba++-dependent blockade of the transcellular conductance exhibited negative cooperativity. The transepithelial osmotic gradient produced by luminal urea produced blebs on apical surfaces, a striking increase in shunt conductance, and a decrease in the shunt Na+/Cl- permselectivity (PNa/PCl), which approached that of free solution. The transepithelial conductance obtained with luminal 800 mM urea, 20 mM Ba++, and 0 K+ was 950 +/- 150 mS/cm2 and provided an estimate of the maximal diffusion resistance of intercellular spaces, exclusive of junctional complexes. The calculated range for junctional dilution voltages owing to interspace salt accumulation during ADH-dependent net NaCl absorption was 0.7-1.1 mV. Since the Ve accompanying ADH-dependent net NaCl absorption is 10 mV, lumen positive, virtually all of the spontaneous transepithelial voltage in the mouse mTALH is due to transcellular transport processes. Finally, we developed a series of expressions in which the ratio of net Cl- absorption to paracellular Na+ absorption could be expressed in terms of a series of electrical variables. Specifically, an analysis of paired measurement of PNa/PCl and Gs was in agreement with an electroneutral Na+:K+:2 Cl- apical entry step. Thus, for net NaCl absorption, approximately 50% of Na+ was absorbed via a paracellular route.

Absorption↗