PubMed Health⌕ Search

Biomedical subjects

K Tabei

Publications and source records attributed to K Tabei.

62 records · Page 4Linked to original sources
PubMed1986

Permselectivity for cations over anions in the upper portion of descending limbs of Henle's loop of long-loop nephron isolated from hamsters.

The permselectivity of the upper portion of long descending limb of Henle (LDLu) was investigated with electrophysiological methods in the isolated perfused tubule preparation of hamster kidney. The diffusion potential (Vt) was determined in three different protocols. In protocol 1, the tubules were initially perfused with modified Krebs Ringer's solution on both sides of the epithelium. Then the bath solution was exchanged consecutively with another solution in which 50 mmol/l NaCl replaced by 50 mmol/l KCl, RbCl, NH4Cl, CsCl, LiCl, NaBr, NaNO3, NaI, Na acetate or 75 mmol/l NaCl replaced by mannitol. The permeabilities for these ions relative to chloride were calculated by Goldman's constant field equation. The segment was found to be cation selective, with all cations being 5-9 times more permeable than all anions. The sequence of permeability was K+ greater than Rb+ greater than Li+ greater than NH+4 = Cs+ greater than or equal to Na+ much greater than Cl- greater than or equal to Br- greater than or equal to NO3- greater than or equal to I- greater than Acetate-. In protocol 2, pure 150 mM NaCl was used for the basal solution to avoid interference by other ions. The bathing solution was exchanged by other solutions which contained 150 mmol/l KCl, NH4Cl, CsCl, RbCl, LiCl, NaI, NaBr, NaNO3, Na acetate or 75 mmol/l NaCl with mannitol. Thus simple biionic substitution was performed. Again, the segment was found to be cation selective, with all cations being 4-10 times more permeable than all anions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Dopaminergic inhibition of the action of vasopressin on the cortical collecting tubule.

The dopaminergic inhibition of the hydrosmotic effect of vasopressin was studied by in vitro perfusion of the cortical collecting tubule isolated from the rabbit kidney. Arginine vasopressin (AVP) 100 microU/ml increased hydrosmotic water permeability (Pf, 10(-3) cm/s) by 11.4 +/- 1.59. Although dopamine 10(-5) M added alone to the bath did not affect Pf, the combined administration of 10(-5) M dopamine and 100 microU/ml AVP reduced the hydrosmotic effect of AVP to to 2.37 +/- 0.34. This inhibitory effect of dopamine was reversed by the simultaneous addition of 10(-5) M metoclopramide, a D2-antagonist. These observations suggest that dopaminergic receptors also exist in the cortical collecting tubule. The dopaminergic inhibition of the hydrosmotic action of AVP may be at least in part responsible for the diuretic action of dopamine.

Animals↗
PubMed1984

Effects of parathyroid hormone and calcitonin on stop-flow patterns of cyclic AMP, sodium, potassium, calcium and inorganic phosphate in thyroparathyroidectomized rabbits.

Conventional stop-flow studies were performed in thyroparathyroidectomized rabbits in order to examine the effects of parathyroid hormone (PTH) and calcitonin on urinary excretion of 3',5'-cyclic adenosine monophosphate (cAMP), Na, K, Ca, and inorganic phosphate (Pi). PTH markedly increased excretion of cAMP in the distal as well as in the proximal fractions. PTH increased Na concentration at the proximal and the distal fractions. K concentration was increased with PTH in all segments, and two prominent peaks were observed at the late proximal and the terminal fractions. Although changes in the pattern of Ca concentration after PTH were similar to those of Na, the pattern of Ca concentration normalized by Na concentration (Ca/Na) showed a decrease in Ca concentration in the late distal fractions. PTH increased Pi concentration in two portions, the proximal and the late distal fractions. Calcitonin slightly increased excretion of cAMP at the midfractions. Calcitonin did not cause any significant changes in the patterns of Na and Pi, but increased Ca concentration in the early distal fractions and K concentration in the late proximal fractions. From these findings we suggest: (a) nephrogenous cAMP responsive to each hormone partly corresponds to nephron distribution of hormone-dependent adenylate cyclase; (b) the sites of action of these hormones are quite distinct in the rabbit kidney; (c) the distal nephron segments play important roles in anticalciuric and phosphaturic actions of PTH, and (d) mechanisms of increases in K excretion by these two hormones may be different.

Adenylyl Cyclases↗
PubMed1983

Early enhancement of fluid transport in rabbit proximal straight tubules after loss of contralateral renal excretory function.

To assess the renal functional adaptation to reduced excretory capacity, we studied whole kidney and single nephron function in anesthetized volume-replete rabbits after unilateral (left kidney) nephrectomy (UNX), ureteral obstruction (UO), or ureteroperitoneostomy (UP). At 24 h, despite the absence of measurable hypertrophy of the contralateral (right) kidney, these procedures significantly increased p-aminohippurate clearance (45-54%) and inulin clearance (CIN) (64-110%) compared with sham-operated control animals. In each group, whole kidney sodium reabsorption increased in proportion to the rise in CIN. To determine whether the intrinsic transport capacity of proximal tubule segments is altered by these maneuvers, we measured fluid volume reabsorption rate (Jv) in isolated superficial proximal straight tubule (PST) segments perfused in vitro, comparing each control tubule (obtained by biopsy of the left kidney immediately before an experimental maneuver) with a corresponding tubule segment obtained 24 h or 7 d later from the contralateral kidney. Control tubule Jv in sham-24 h animals averaged 0.48 +/- 0.04 nl/(min X mm). Jv did not change significantly at 24 h or 7 d after sham maneuvers but increased significantly at 24 h after UNX [delta Jv = 0.13 +/- 0.03 nl/(min X mm)], UO [delta Jv = 0.10 +/- 0.04 nl/(min X mm)], and UP [delta Jv = 0.13 +/- 0.04 nl/(min X mm)]. Jv remained increased by similar amounts at 7 d after UNX and UO. To evaluate whether an increase in glomerular filtration rate (GFR) might be the stimulus to this augmentation in Jv values, methylprednisolone (MP) (15 mg/kg per d) was administered daily to sham-operated animals, a maneuver which induced a 73% rise in CIN by day 5. This procedure also produced a significant increase in Jv in PST at 5 d [delta Jv = 0.16 +/- 0.05 nl/(min X mm)]. The increase in Jv evident in each group at 5 or 7 d was paralleled by an equivalent change in tubule cell volume and apparent tubule luminal surface area in UNX-7d and MP-5d; no such increments in these indices, or in apparent tubule serosal surface area were evident at 24 h in any group. Thus, a 50% reduction in renal excretory function in the rabbit provokes adjustments in renal plasma flow rate and GFR in the contralateral kidney, which are evident by 24 h. The concurrent change in Jv in PST is closely related to CIN or some associated hemodynamic process, but does not appear to require an increase in tubule cell volume or apparent surface area. The ability to detect these small in vivo changes in Jv may derive from the enhanced sensitivity of paired-kidney experiments using tubule segments obtained by renal biopsy.

Animals↗
PubMed1982

Efficacy of charcoal hemoperfusion in paraquat poisoning.

We studied the efficiency of in vitro and in vivo charcoal hemoperfusion for the removal of paraquat. At a flow rate of 200 ml/min, 93-99% of paraquat in 4 L of solution (5, 10, 100 ppm) was removed in less than 160 min. The disappearance half-time was 16 min 10 sec. At 100 ml/min, it was 49 min 30 sec. Of 23 paraquat poisoning cases, 15 patients underwent hemoperfusion (HP) of which 10 died of respiratory failure within 28 days (7.6 +/- 2.9) and 5 survived without pulmonary complications. Of eight patients who did not receive HP, six died of respiratory failure within 97 days (33.4 +/- 18.8), even when their general condition was good upon admission. Two who vomited the ingested paraquat immediately survived without HP, and their paraquat concentration in urine was less than one ppm on admission. In one patient, whose paraquat concentration in blood was followed serially, 99% of the paraquat was removed from circulating blood by a single hemoperfusion. We conclude that charcoal hemoperfusion is effective for the removal of paraquat from blood in vivo and from solution in vitro. Hemoperfusion may also improve survival after paraquat ingestion, but further data are needed.

Adolescent↗
PubMedDate not supplied

The effect of EGF on electrolyte transport is mediated by tyrosine kinases in the rabbit cortical collecting duct.

Epidermal growth factor (EGF) inhibits amiloride-sensitive Na(+) conductance in the apical membrane of the isolated rabbit cortical collecting duct. However, there is no information on the relationship between electrolyte transport and tyrosine kinase. We examined the effect of EGF on transport of potassium and chloride as well as sodium and the roles of tyrosine kinases in the rabbit cortical collecting duct using in vitro isolated tubular microperfusion. Basolateral EGF depolarized the transepithelial voltage in a dose-dependent manner within a concentration range of 10(-10) in 10(-8) M. Basolateral ouabain and luminal amiloride completely abolished EGF-induced depolarization. However, luminal BaCl(2) did not abolish its depolarization. To confirm the mechanism, sodium, potassium, and chloride fluxes were measured in the presence of 10(-10) M EGF. EGF significantly decreased the lumen-to-bath isotope flux of sodium and chloride from 93.6+/-12.5 to 61.1+/-9.6 pmol/mm/min (n = 5, p<0.05) and from 86.6+/-10.0 to 54. 8+/-9.7 pmol/mm/min (n = 10, p<0.01), respectively. EGF also decreased net potassium secretion from -27.7+/-5.9 to -7.8+/-1.5 pmol/mm/min (n = 6, p<0.01). To examine whether EGF-induced depolarization is mediated by tyrosine kinase, tyrosine kinase inhibitors were applied from the basolateral side. Pretreatment with 1 microg/ml herbimycin A for 120 min completely abolished EGF-induced depolarization (90.9+/-5.4%, n = 4; NS). Herbimycin A itself also did not change the lumen-to-bath isotope flux of sodium and completely abolished the inhibition of Na(+) absorption on EGF action (control 65.4+/-6.8, herbimycin A 61.8+/-6.3, EGF with herbimycin A 60.0+/-4.4 pmol/min/mm, n = 5; NS). In conclusion, EGF depolarizes transepithelial voltage by inhibiting sodium transport primarily and potassium and chloride transport secondarily. These effects were blocked by nonspecific tyrosine kinase inhibitors.

Animals↗