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At least 343 records · Page 19Linked to original sources
PubMed1992

A possible relationship between KCl symport and basolateral K(+)-conductance in Necturus gallbladder epithelial cells.

1. Apical membrane potential (Va), transepithelial potential (VT), fractional apical voltage ratio (FVa = delta Va/delta VT), tissue resistance (RT), and intracellular Cl- (aiCl) and K+ (aiK) activities were measured in isolated gallbladders maintained between oxygenated bicarbonate-free physiological media (23 degrees C, pH 7.2 or 8.2) in a divided chamber. The basolateral membrane potential (Vb) was calculated from the measured values of Va and VT. 2. Cl- removal from the serosal medium (which should accelerate coupled basolateral KCl exit) significantly depolarized Vb, decreased aiCl, decreased FVa, increased RT, and attenuated the depolarization of Vb (delta Vb) induced by high K+ added to the serosal side. These changes are consistent with a decrease in the K(+)-conductance of the basolateral membrane (gbK). 3. Addition of furosemide (an inhibitor of KCl cotransport) to the serosal medium induced significant increases in Vb, FVa, and high K(+)-induced delta Vb, indicating an increase in gbK. 4. In the presence of serosal furosemide, Cl- removal from the serosal medium did not significantly alter Vb, aiCl or delta Vb from their corresponding values when serosal Cl- was present. 5. Serosal furosemide had no significant effect on aiK and aiCl measured with double-barreled ion-selective microelectrodes. 6. These results suggest the possibility of a reciprocal relationship between gbK and the rate of basolateral KCl cotransport. This may contribute to the maintenance of aiK in gallbladder epithelial cells.

Animals↗
PubMed1983

Distribution of monoamine oxidase activity in tissues of the urodeles Ambystoma tigrinum (tiger salamander) and Necturus maculosus (mudpuppy).

1. Monoamine oxidase (MAO) activity was determined fluorometrically in tissues of adult mudpuppies, and pre- (young) and post- (adult) metamorphic tiger salamanders. 2. From responses to specific inhibitors it was determined that 95% activity was MAO type A in all tissues. 3. In young salamanders MAO activity was greater in brain and intestine of males than of females, and was considerably higher in kidney of both sexes and in intestine of males compared to adults. 4. MAO activity was distributed differently in the mudpuppy compared to the salamander. Intestine and liver contained high activity and brain had relatively little MAO activity compared to salamander. 5. The apparent Michaelis constant of MAO activity in the different groups and tissues was generally similar, suggesting a similarity of the MAO molecule.

Aging↗
PubMed1986

Histamine and histamine receptors: behavioral thermoregulation in the salamander Necturus maculosus.

Low doses (0.01, 0.1 mg/kg, i.p.) of histamine (HA) caused selection of significantly lower temperatures, and higher doses (0.5, 1.0 mg/kg) increased temperatures by mudpuppies in linear thermal gradients. Injection of the HA precursor, L-histidine (500 mg/kg) produced an increase in the temperatures selected. Results from injections of HA H1-receptor agonist (2-pyridylethylamine) and antagonist (pyrilamine), and H2-receptor agonist (dimaprit) and antagonist (cimetidine) had significant effects on thermoregulation; H1-receptors may mediate behavioral hyperthermia and H2-receptors behavioral hypothermia. Responses to these histaminic compounds are significantly influenced by the time of day at which the responses are measured and by season and acclimation temperature. The equivalent behavioral responses in both endotherms and ectotherms to agents which produce physiological hyperthermia and hypothermia are probably behavioral hypothermia ("cold seeking") and behavioral hyperthermia ("heat seeking"), respectively.

Animals↗
PubMed1990

Apical membrane Na+/H+ exchange in Necturus gallbladder epithelium. Its dependence on extracellular and intracellular pH and on external Na+ concentration.

Intracellular microelectrode techniques and extracellular pH measurements were used to study the dependence of apical Na+/H+ exchange on mucosal and intracellular pH and on mucosal solution Na+ concentration ([Na+]o). When mucosal solution pH (pHo) was decreased in gallbladders bathed in Na(+)-containing solutions, aNai fell. The effect of pHo is consistent with titration of a single site with an apparent pK of 6.29. In Na(+)-depleted tissues, increasing [Na+]o from 0 to values ranging from 2.5 to 110 mM increased aNai; the relationship was well described by Michaelis-Menten kinetics. The apparent Km was 15 mM at pHo 7.5 and increased to 134 mM at pHo 6.5, without change in Vmax. In Na(+)-depleted gallbladders, elevating [Na+]o from 0 to 25 mM increased aNai and pHi and caused acidification of a poorly buffered mucosal solution upon stopping the superfusion; lowering pHo inhibited both apical Na+ entry and mucosal solution acidification. Both effects can be ascribed to titration of a single site; the apparent pK's were 7.2 and 7.4, respectively. Diethylpyrocarbonate (DEPC), a histidine-specific reagent, reduced mucosal acidification by 58 +/- 4 or 39 +/- 6% when exposure to the drug was at pHo 7.5 or 6.5, respectively. Amiloride (1 mM) did not protect against the DEPC inhibition, but reduced both apical Na+ entry and mucosal acidification by 63 +/- 5 and 65 +/- 9%, respectively. In the Na(+)-depleted tissues mean pHi was 6.7. Cells were alkalinized by exposure to mucosal solutions containing high concentrations of nicotine or methylamine. Estimates of apical Na+ entry at varying pHi, upon increasing [Na+]o from 0 to 25 mM, indicate that Na+/H+ exchange is active at pHi 7.4. Intracellular H+ stimulated apical Na+ entry by titration of more than one site (apparent pK 7.1, Hill coefficient 1.7). The results suggest that external Na+ and H+ interact with one site of the Na+/H+ exchanger and that cytoplasmic H+ acts on at least two sites. The external titratable group seems to be an imidazolium, which is apparently different from the amiloride-binding site. The dependence of Na+ entry on pHi supports the notion that the Na+/H+ exchanger is operational under normal transport conditions.

Animals↗
PubMed1986

Carbonic anhydrase inhibition and cell volume regulation in Necturus gallbladder.

Gallbladder epithelial cells transport salt and water isotonically as the renal proximal tubule. The cells also have the property of regulating their cell volume in response to osmotic stress (Fisher et al. 1981, Persson & Spring 1982, Fisher & Spring 1984, Foskett & Spring 1985). The volume-regulating phenomenon is the result of a balance between cell uptake of salt and water at the luminal membrane and exit at the basolateral membrane. Different properties regarding volume regulatory increase and decrease have been found (Eriksson & Spring 1982 and Larson & Spring 1983). The present study links fluid transport and volume regulatory increase of the cell. First we concluded from histological techniques that carbonic anhydrase is present in the cell membrane or in the vicinity of the epithelial cells. Then we measured a decreased net fluid transport in the presence of increasing concentrations of the carbonic anhydrase inhibitor acetazolamide. We showed that the volume regulatory increase is substantially slowed down and that the steady-state volume of the cells changed when carbonic anhydrase was inhibited. Our conclusion is that the rate of CO2 hydration was a limiting step, at carbonic anhydrase inhibition, in both the net transfer of salt and water and also in the ability of the cells to efficiently regulate their volume.

Acetazolamide↗
PubMedDate not supplied

Activation of NMDA receptors is required for the initiation and maintenance of walking-like activity in the mudpuppy (Necturus Maculatus).

We hypothesized that blocking the activation of N-methyl-D-aspartate (NMDA) receptors prevents the initiation of walking-like activity and abolishes the ongoing rhythmic activity in the spinal cord-forelimb preparation from the mudpuppy. Robust walking-like movements of the limb and rhythmic alternating elbow flexor-extensor EMG pattern characteristic of walking were elicited when continuous perfusion of the spinal cord with solution containing D-glutamate. The frequency of the walking-like activity was dose-dependent on the concentration of D-glutamate in the bath over a range of 0.2 to 0.9 mmol/L. Elevation of potassium concentrations failed to induce walking-like activity. Application of the selective antagonist 2-amino-5-phosphonovalerate (AP-5) produced dose-dependent block of the initiation and maintenance of walking-like activity induced by D-glutamate. Complete block of the activity was achieved when the concentration of AP-5 reached 20 micromol/L. Furthermore, application of L-701,324 (a selective antagonist of the strychnine-insensitive glycine site of NMDA receptor) (1-10 micromol/L) also resulted in complete block of the walking-like activity. In contrast, application of the non-NMDA receptor antagonist 6-cyno-7-nitroquinoxaline-2,3-dione (CNQX) (1-50 micromol/L) induced a dose-dependent inhibition of the burst frequency but failed to result in a complete block. Only at concentration as high as 100 micromol/L, did CNQX cause complete block of the rhythmic activity, presumably through nonspecific action on the strychnine-insensitive glycine site of NMDA receptors. These results suggest that activation of NMDA receptors is required for the initiation and maintenance of walking-like activity. Operation of non-NMDA receptors plays a powerful role in the modulation of the walking-like activity in the mudpuppy.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMedDate not supplied

Anatomical organization of motoneurons and interneurons in the mudpuppy (Necturus maculosus) brachial spinal cord: the neural substrate for central pattern generation.

The isolated brachial spinal cord of the mudpuppy is useful for studies of neural networks underlying forelimb locomotion, but information about its anatomy is scarce. We addressed this issue by combining retrograde labeling with fluorescent tracers and confocal microscopy. Remarkably, the central region of gray matter was aneural and contained only a tenuous meshwork of glial fibers and large extracellular spaces. Somata of motoneurons (MNs) and interneurons (INs), labeled retrogradely from ventral roots or axons in the ventro-lateral funiculus, respectively, were confined within a gray neuropil layer abutting the white matter borders, while their dendrites projected widely throughout the white matter. A considerable fraction of labeled INs was found contralaterally with axons crossing beneath a thick layer of ependyma surrounding the central canal. Dorsal roots (DRs) produced dense presynaptic arbors within a restricted dorsal region containing afferent terminations, within which dorsally directed MN and IN dendrites mingled with dense collections of synaptic boutons. Our data suggest that a major fraction of synaptic interactions takes place within the white matter. This study provides a detailed foundation for electrophysiological experiments aimed at elucidating the neural circuits involved in locomotor pattern generation.

Animals↗