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PubMed1979

Effect of potassium deficiency on papillary plasma flow in the rat.

Chronic potassium (K+) deficiency has been shown previously to cause a reduction in solute content in the renal papilla, an effect that is potentially important as a contributing factor to the concentrating defect seen in this circumstance. The cause of the decrease in papillary solute content has not been adequately explained. Because alterations in the blood flow rate through the renal papilla may affect the solute content of the papilla, the present experiments examined the effect of chronic K+ deficiency on papillary plasma flow (PPF) in the rat. PPF was measured by the radioactive albumin accumulation technique. Sprague-Dawley rats were fed identical quantities of water and either a normal or a K+-deficient diet for 21 days. Total GRR in the control rats, 1.7 +/- 0.17 (SE) ml/min, was similar to that in K+-deficient rats, 1.4 +/- 0.14 ml/min (P greater than 0.01). Total [3H]PAH clearance was also comparable in the two groups, i.e., 4.4 +/- 0.47 in control and 4.7 +/- 0.45 ml/min in K+-deficient rats (P greater than 0.06). PPF was significantly lower in K+-deficient rats, 19.7 +/- 1.1 ml-min-1-100 g-1, than in control rats, 59.8 +/- 1.6 ml-min-1-100 g-1 (P less than 0.001). The decrease in PPF in the K+-deficient rat may reflect a reduction in perfusion to the juxtamedullary nephrons, thereby resulting in a diminution in both solute delivery and blood flow to the papilla.

Animals↗
PubMed1986

Effects of semi-starvation and potassium deficiency on the concentration of [3H]ouabain-binding sites and sodium and potassium contents in rat skeletal muscle.

1. Using vanadate-facilitated [3H]ouabain binding, the effect of semi-starvation on the total concentration of [3H]ouabain-binding sites was determined in samples of rat skeletal muscle. When 12-week-old rats were semi-starved for 1, 2 or 3 weeks on one-third to half the normal daily energy intake, the [3H]ouabain-binding site concentration in soleus muscle was reduced by 19, 24 and 25% respectively. In extensor digitorum longus, diaphragm and gastrocnemius muscles the decrease after 2 weeks of semi-starvation was 15, 18 and 17% respectively. The decrease was fully reversible within 3 d of free access to the diet. Complete deprivation of food for 5 d caused a reduction of 25% in soleus muscle [3H]ouabain-binding-site concentration. It was excluded that the reduction in [3H]ouabain binding was due to a reduced affinity of the binding site for [3H]ouabain. 2. Semi-starvation of 12-week-old rats for 3 weeks caused a reduction of 45 and 53% in 3,5,3'-triiodothyronine (T3) and thyroxine (T4) levels respectively. As reduced thyroid hormone levels have previously been found to decrease [3H]ouabain-binding-site concentration in skeletal muscle, this points to the importance of T3 and T4 in the down-regulation of the [3H]ouabain-binding-site concentration in skeletal muscle with semi-starvation. Whereas potassium depletion caused a decrease in K content as well as in [3H]ouabain-binding-site concentration in skeletal muscles, semi-starvation caused only a tendency to a decrease in K content. Thus, K depletion is not a major cause of the reduction in [3H]ouabain-binding-site concentration with semi-starvation. 3. Due to its high concentration of Na,K pumps, skeletal muscle has a considerable capacity for clearing K from the plasma as well as for the binding of digitalis glycosides. Semi-starvation causes a severe reduction in the total skeletal muscle pool of Na,K pumps and may therefore be associated with impairment of K tolerance and increased digitalis toxicity.

Animals↗
PubMed1973

Effects of potassium deficiency on the photosynthesis and respiration of leaves of sugar beet.

Sugar beet plants (Beta vulgaris L. var. F5855441) were germinated and cultured under standardized environmental conditions for 28 days. Potassium deficiency was then induced by withholding K from the culture solution. Changes in CO(2) and water vapor exchange rates and surface temperatures of individual attached leaves were measured with time after K cut-off, along with changes in the concentrations of the leaf minerals K, Na, Ca, Mg, Fe, Mn, Cu, and Zn. During the 1st week after K cut-off the concentration of Na in the leaf blade increased from 200 to 1000 milliequivalents per kilogram dry matter while K decreased from 1500 to 300 milliequivalents per kilogram. During the subsequent 2 weeks, both Na and K concentrations decreased. The concentrations of other leaf minerals, except Mn, were little affected by K cut-off. Photosynthetic CO(2) uptake per unit area decreased linearly with time after cut-off and attained one-third of the control rate after 21 days. Low K apparently decreased photosynthesis through an increase in mesophyll resistance to CO(2) (r(m)) from 2.8 to 5.3 seconds per centimeter in 21 days. Leaf (mainly stomatal) diffusion resistance (r'(1)) increased only slowly during the first 15 days from 0.3 to 0.5 second per centimeter, eventually reaching 1.6 seconds per centimeter at 21 days. Low K progressively decreased the photorespiratory evolution of CO(2) into CO(2)-free air, but steadily increased the rate of CO(2) evolution in dark.

Journal Article↗