Renal K+ retention in physiological circumstances: focus on adaptation of the distal nephron and cross-talk with Na+ transport systems

Abstract

Consumption of salt (NaCl) and potassium (K⁺) has been completely modified, switching from a rich-K⁺/low-NaCl diet in the hunter-gatherer population to the opposite in the modern, westernized population. The ability to conserve K⁺ is crucial to maintain the plasma K⁺ concentration in a physiological range when dietary K⁺ intake is decreased. Moreover, a chronic reduction in the K⁺ intake is correlated with an increased blood pressure, an effect worsened by a high-Na⁺ diet. The renal adaptation to a low-K⁺ diet in order to maintain the plasma K⁺ level in the normal range is complex and interconnected with the mechanisms of the Na⁺ balance. In this short review, we will recapitulate the general mechanisms allowing the plasma K⁺ value to remain in the normal range, when there is a necessity to retain K⁺ (response to low-K⁺ diet and adaptation to gestation), by focusing on the processes occurring in the most distal part of the nephron. We will particularly outline the mechanisms of K⁺ reabsorption and discuss the consequences of its absence on the Na⁺ transport systems and the regulation of the extracellular compartment volume and blood pressure.

Keywords: ATP12A; blood pressure; extracellular compartment; potassium balance; sodium balance.

FIGURE 1

(A) Schematic representation of K⁺ repartition in different compartments of the organism. The priority of the organism is to maintain the extracellular K⁺ concentration into a narrow range despite the variations in K⁺ intake; this value corresponds to 70 mmol of K⁺ for a human weighing about 70 kg. For this purpose, K⁺ may be pumped or released from internal stores (internal balance) or may be reabsorbed or secreted in the feces and urine (external balance) in order to excrete exactly the amount of K⁺ ingested. (B) Evolution of Na⁺ and K⁺ intakes adapted from Meneton et al. (2004).

FIGURE 2

Schematic representation of the renal key players involved in the external K⁺ balance. To maintain equilibrium between the K⁺ input and output, the kidney is equipped with nephron segments, the distal convoluted tubule (DCT), and the collecting duct (CD) that contribute to K⁺ secretion or reabsorption. CD is composed of different cell types expressing specific ion and water transporters: the A-type intercalated cells (AICs), the principal cells (PCs), and the B-type intercalated cells (BICs).