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PubMed1994

An X-ray microanalysis study of Locusta Malpighian tubule cell function using rubidium.

Intracellular distributions of Na, K, Mg, Ca, Cl, P, and S were determined in type 1 Malpighian tubule cells of Locusta using X-ray microanalysis. K showed a gradient of increasing concentration from basal to apical surfaces. No other element showed this distribution. Na was below the detection limit. Three types of dark body were present in cytoplasm; one rich in Ca and P and two rich in K and P. Incubation in Rb-Ringer solution resulted in a dramatic fall in cellular K that was not completely replaced by Rb. The distribution of Rb mimicked that of K. Na levels were significantly increased, but the total intracellular monovalent metal concentration was less than in controls. Other elements were little affected. Rb replaced K in dark bodies. Tubules continued to secrete K-rich urine in Rb-Ringer solution even though intracellular [K] was low. Little Rb+ was secreted and Na+ secretion was unchanged. The possible role of dark bodies as a source of secreted K+ is discussed.

Animals↗
PubMed1986

Effect of ADH on rubidium transport in isolated perfused rat cortical collecting tubules.

Unidirectional fluxes of 86Rb+ were measured as an indicator of potassium transport in isolated rat cortical collecting tubules perfused and bathed at 38 degrees C with isotonic solutions in which Rb+ replaced K+. Under control conditions the lumen-to-bath flux (Jl----b) was significantly less than the bath-to-lumen flux (Jb----l), indicating net Rb+ secretion. Net secretion increased approximately 180% after addition of 100 microU/ml of arginine vasopressin (ADH) to the bathing solution, due to a rapid and reversible increase in Jb----l from 4.6 +/- 0.8 to 9.0 +/- 1.9 pmol X min-1 X mm-1 with no significant change in Jl----b. The ADH effect was completely inhibited by 2 mM luminal Ba2+. The average transepithelial voltage (Ve) was not significantly different from zero in the control period but became lumen negative (-5 to -10 mV) after ADH. With 10(-5) M amiloride in the lumen Ve was lumen positive (+2 to +4 mV) and was unaltered by ADH or Ba2+, yet ADH produced a significant but attentuated increase in Jb----l with no change in Jl----b. The results indicate that ADH augments net K+ secretion either by an increase in the Ba2+-sensitive conductance of the apical membrane or by an increase in the electrochemical potential driving force for net Rb+ secretion through this pathway.

Amiloride↗
PubMed1992

Rubidium absorption and proton secretion by rabbit outer medullary collecting duct via H-K-ATPase.

Multiple lines of evidence support the hypothesis that the outer medullary collecting duct from the inner stripe (OMCDi) possesses a functional proton-potassium-activated adenosinetriphosphatase (H-K-ATPase). To examine the effect of inhibition of H-K-ATPase on Rb efflux, we measured the Rb tracer rate efflux coefficient (KRb) across the OMCDi of animals adapted to a K-restricted diet using the selective K-competitive H-K-ATPase inhibitor, Sch 28080. Sch 28080 (10 microM) did not significantly alter transepithelial voltage (VT) but significantly decreased KRb by 41%. We further examined the effect of 10% peritubular CO2 on KRb and the subsequent effect of Sch 28080 (10 microM) on KRb. After exposure to 10% CO2 for 120 min, vehicle-treated tubules exhibited a small but significant increase in KRb without a significant change in VT. In contrast, 10 microM Sch 28080 significantly decreased KRb by 44% without affecting VT. The lack of an effect of H-K-ATPase inhibition on VT in the presence of either 5% or 10% CO2 was in marked contrast to the effect of carbonic anhydrase inhibition (CAI). CAI consistently and significantly decreased VT either in the presence of 5% or 10% CO2. To address whether H-K-ATPase also participates in proton secretion we examined the effect of Sch 28080 (10 microM) on net bicarbonate absorption by the OMCDi of rabbits fed a normal rabbit ration and rabbits adapted to a K-restricted diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1992

Mechanisms of rubidium permeation by rabbit cortical collecting duct during potassium restriction.

To examine the pathways of K permeation in the cortical collecting duct (CCD) from K-restricted rabbits, we studied the effects of the following three maneuvers: 1) luminal amiloride addition; 2) luminal Ba addition; and 3) luminal Na removal. Luminal addition of amiloride (1 mM) significantly increased the 86Rb lumen-to-bath efflux coefficient (KRb), and this effect was fully blocked by the presence of 2 mM luminal Ba. Addition of 2 mM luminal Ba reduced KRb both in the absence of luminal Na and in the presence of luminal Na. In contrast to the effect of amiloride addition, removal of luminal Na significantly increased KRb, but neither 2 mM luminal Ba nor 4 mM luminal Ba totally abolished this effect. However, simultaneous addition of luminal Ba and Sch 28080 (10 microM) fully inhibited the increase in KRb upon luminal Na removal, indicating that luminal Na removal enhances Rb efflux in part via H-K-adenosinetriphosphatase (H-K-ATPase). To test whether Na acts as a partial agonist for cation efflux via the H-K-ATPase we examined the effect of Sch 28080 on the 22Na lumen-to-bath efflux coefficient (KNa). These studies were conducted in the presence of 0.1 mM luminal amiloride to block fully apical conductive Na efflux, and the effect of Sch 28080 on KNa was examined at two different ambient K concentrations. In the presence of 0.5 mM K, Sch 28080 (10 microM) significantly inhibited KNa from 47.6 +/- 4.8 to 35.0 +/- 6.8 nm/s (P < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Comparison of rubidium-86 and potassium-42 fluxes in rat aorta.

Potassium transport has frequently been assessed by measurement of 86Rb. However, recent reports indicated that the K ion channels are selective to K over Rb. Therefore, the purpose of this study was to evaluate whether the basal and stimulated fluxes of Rb and K were equivalent in rat aorta in the absence of endothelium. The ouabain-sensitive (active) uptake of 86Rb and 42K was similar. However, the basal 86Rb efflux was only 80% of the 42K efflux. Norepinephrine and KCl depolarization stimulated 86Rb and 42K effluxes via a calcium-dependent process. The stimulated 86Rb efflux ranged from 56 to 74% of the 42K efflux. Diltiazem reduced the KCl-stimulated 86Rb and 42K effluxes. The 86Rb efflux was 82% of the 42K efflux in the presence of KCl plus diltiazem, similar to that under basal conditions. Substitution of Rb for K in the incubation solution was associated with a marked increase in spontaneous contractile activity. There was no change in the norepinephrine concentration required for a 50% stimulation of contraction or 86Rb efflux from Rb-loaded tissues. We conclude from these studies that the basal and calcium-activated potassium channels are selective for K over Rb and therefore 86Rb fluxes quantitatively underestimate that of 42K. However, 86Rb is an appropriate substitute for the measurement of active K transport.

Animals↗
PubMed1987

Influence of furosemide on rubidium-86 uptake and alpha-adrenergic responsiveness of arterial smooth muscle.

Furosemide-induced inhibition of 86Rb uptake was measured in rat and rabbit aorta and compared with its ability to inhibit contractions induced by alpha-adrenergic agonists. In both rat and rabbit tissues, furosemide defined a portion of 86Rb uptake (IC50 = 2.5 microM) which was distinct from the ouabain-sensitive fraction. Furosemide-sensitive 86Rb uptake was [Cl-]ext dependent and required Na+ and K+ for optimal activity, suggesting that it reflected a Na+-K+ cotransport process. Furosemide-sensitive 86Rb uptake was found to be greater in HEPES buffer than in bicarbonate buffer. Phenylephrine-induced contractions of rat and rabbit aorta were inhibited by furosemide; however, rat responses were far more sensitive. Agonist-induced uptake of 45Ca was reduced by furosemide in rat aorta, but not in rabbit aorta. Agonist-induced 45Ca efflux stimulation was reduced in both species. These findings indicate the presence in arteries of a furosemide-sensitive, Cl-dependent Na+-K+ cotransport process. Along with other monovalent transport processes, it may modulate Ca2+ availability and thereby influence arterial contractility.

Animals↗
PubMed1990

Lenticular rubidium uptake and plasma renin activity in weanling cataract-prone salt-sensitive rats.

Our earlier studies of cataracts in Dahl salt-sensitive (DS) rats suggested the possibility of altered lens ion transport as a contributing factor in cataractogenesis in this genetic model. We also observed that those weanling DS rats with the greatest pressor response to a high salt diet eventually developed cataracts, and that changes in salt intake modified cataract formation. In the present studies, we measured lens 86Rb uptake as an index of sodium-potassium adenosine triphosphatase [(Na+,K+)-ATPase] activity in weanling DS rats before the development of cataracts or sustained hypertension. Additionally, plasma renin activity was measured to indirectly assess our hypothesis that the difference between cataract-prone DS rats and DS rats unlikely to develop cataracts might be a difference in degree of salt sensitivity. At the age of 4 weeks, 50 DS and 25 salt-resistant (DR) rats were given a high sodium diet for 2 weeks, at which time the rats were divided into three groups based on the systolic blood pressure response, that is, cataract-prone DS rats with systolic blood pressure equal to or greater than 155 mm Hg, DS rats unlikely to develop cataracts with systolic blood pressure less than or equal to 125 mm Hg, and DR rats. Lens and aqueous humor Na+ and K+, lens dry weight, and water content were not significantly different among the three groups of weanling rats. Plasma renin activity was lowest in cataract-prone DS rats and low in DS rats unlikely to develop cataracts when compared with values in DR rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗