Characteristics of the Relationship between the Flow Rate of Tubular Fluid and Potassium Transport in the Distal Tubule of the Rat

Abstract

A B S T R A C T The flow rate of tubular fluid has been suggested as one of several factors which may influence potassium transport in the distal convoluted tubule of the kidney. In the present micropuncture studies, the relationship between the flow rate of distal tubular fluid and potassium transport was examined in four groups of rats. Three groups of rats (I, II, and IV) were fed normal rat chow before study whereas one group (III) was fed chow containing 10% KC1. Group II received 10-20 pg/kg per h of d-aldosterone throughout the study.Distal tubular potassium transport in groups I, II, and III was examined before and after an increase in the flow rate of distal tubular fluid as induced by the infusion of an isotonic saline-bicarbonate solution equivalent to 10% of body weight. In group IV, distal tubular potassium transport was examined before and after enhancement of the flow rate by the infusion of hypertonic (15%) mannitol.In all four groups, distal tubular potassium secretion increased as the flow rate of tubular fluid increased. The nature of the relationship between distal tubular potassium transport and tubular fluid flow rate, however, was influenced by the extent to which the tubular fluid to plasma potassium ratio in the late distal tubule varied as the flow rate increased. As the flow rate was increased this ratio decreased significantly and to a comparable extent in groups I and II. In groups III and IV, on the other hand, this ratio was essentially identical during hydropenia and after the increase in the flow rate of tubular fluid. As a result, the increment in the amount of potassium present at the late distal tubule, which occurred as the flow rate increased, was significantly greater in groups III and IV than in groups I and II. The contrast in the relationship between the This work was presented in part at the American Society of Nephrology, Washington, D. C., November, 1973. Received for publication 10 May 1974 and in revised form 16 August 1974.flow rate of distal tubular fluid and potassium transport which were observed, probably reflects differences in the net driving force for cell to lumen potassium movement. Seemingly, the net driving force for potassium movement was maintained, as the flow rate of tubular fluid increased, by chronic potassium loading in group III and by hypertonic mannitol infusion in group IV.In groups I and II, the net driving force for potassium movement decreased as the flow rate of tubular fluid increased. However, the net driving force did not decrease in proportion to the increase in flow rate since potassium secretion was increased by increments in flow rate in these groups as well. We conclude that our results are consistent with the view that the flow rate of tubular fluid is a factor which can affect distal tubular potassium transport. However, the nature of the relationship between the flow rate of tubular fluid and potassium transport appears to depend upon the degree to which the driving force for cell to lumen potassium movement changes as the flo...

The effects of intravenous injection of .ALPHA.-human atrial natriuretic polypeptide on blood pressure, renal hemodynamics and urinary kinin excretion in anesthetized rabbits.

“…Borenstein et al (1983) reported that injection of atrial extract into anesthetized rats increased total and medullary blood flow in the kidney. In the present study, the prolonged kaliuresis was accompanied by the diuresis, which suggests that urine flow into the distal tubule may have increased after the injection of a-hANP, since it has been shown that potassium secretion is increased when flow into the distal tubule is increased (Malnic et al 1966;Morgan and Berliner 1969;Kunau et al 1974; Khuri et al 1975;Reineck et al 1975;Diezi et al 1976). This increase in urine flow into the distal tubule could have been elicited by the dissipation of corticomedullary osmotic gradient by medullary washout.…”

Potentiation of renal effects of atrial natriuretic factor-(99-126) by SQ 29,072.

“…These findings are consistent with the proposal that ANF increases sodium excretion by inhibition of sodium transport in the collecting ducts (see Reference 46 for review) as well as by changing tubular flow and sodium delivery to the distal tubule, conditions known to influence potassium transport. 47 - 48 Any changes in tubular flow due to alterations in renal hemodynamics are more likely to be sustained under conditions in which renal perfusion pressure is maintained or decreased only transiently, that is, in the absence of SQ 29,072 in the present experiments. Should the inhibition of collecting duct sodium transport by ANF proceed independently of the changes in flow, sodium excretion could increase without a concurrent rise in potassium excretion or urine volume.…”

Epoxyeicosatrienoic Acid Activates BK Channels in the Cortical Collecting Duct

“…Alternatively, an increase in tubular flow rate could directly stimulate ENaC activity possibly by altering the cleaved versus noncleaved ENaC at the apical membrane regardless the presence of 11,12-EET. 53 Because HK intake has also been shown to increase the tubule flow rate in the distal nephron, 54 the high flow rate could directly activate ENaC and thereby increase the driving force for K secretion. Increased tubule flow rate has been shown to stimulate BK channeldependent K secretion.…”

“…Because HK intake also increases tubule flow rate, 54 it is possible that HK-induced increase in tubule flow is partially responsible for high 11,12-EET levels in the CCD from HK-adapted rats. Moreover, it is conceivable that inhibiting CYP-epoxygenase could also attenuate BK channel-dependent K secretion in response to HK intake; however, it is likely that factors other than EET are also involved in stimulating BK channel-dependent K secretion in response to HK intake.…”