A reductionist approach to studying renal claudins provides insights into tubular permeability properties

Tight junctions are molecular seals between cells that prevent the leaking of fluids, ions, and other small solutes across cavities and compartments in multicellular organisms. They are mainly composed of claudin and occludin transmembrane proteins, and other proteins such as tricellulin and JAM (junctional adhesion molecule). All these proteins are 4-pass transmembrane proteins, except JAM, which is a single-pass transmembrane protein belonging to the immunoglobulin superfamily. The...

The renal tubule is divided into three parts: the proximal convoluted tubule (PCT), the Loop of Henle (LOH), and the distal convoluted tubule (DCT).
Proximal Convoluted Tubule (PCT):
The PCT is the initial segment of the renal tubule, extending from the Bowman's capsule that encloses the glomerulus. Its convoluted structure and microvilli-lined cells increase the surface area for reabsorption. The PCT reabsorbs glucose, amino acids, sodium, and water from the filtrate, ensuring essential...

Once the process of glomerular filtration is completed, blood carrying unfiltered drug molecules traverses through efferent arterioles and makes its way into the peritubular capillaries in the proximal tubule. A variety of carriers play a pivotal role in actively secreting drugs from these peritubular capillaries into the tubular fluid. The organic anion transporter transfers acidic drugs, against an electrochemical gradient, from the peritubular capillaries into the renal tubule cells and...

Tubular secretion and reabsorption are two critical processes in the nephron tubule of the kidneys. When the fluid filtered from the glomerulus enters the proximal convoluted tubule, it is referred to as filtrate, and its composition changes due to tubular reabsorption and secretion.
Tubular reabsorption is a selective process that starts when the filtrate enters the proximal tubules. It involves substances traveling through the transcellular route (through the tubule cell and peritubular...

The early phase of the DCT manages the reabsorption of approximately 10-15% of filtered water, 5–10% of filtered sodium, and 5–10% of filtered chloride. This process is facilitated by Na+–Cl− symporters in apical membranes and sodium-potassium pumps, as well as Cl− leakage channels in basolateral membranes. The early DCT also stands out as a site where parathyroid hormone (PTH) stimulates calcium reabsorption, depending on the body's requirements.
The distal...

The thick ascending limb of the nephron loop has Na+–K+–2Cl− symporters in the apical membranes of its cells. These symporters simultaneously reclaim one sodium ion, one potassium ion, and two chloride ions from the tubular fluid. Sodium ions are actively transported into the interstitial fluid at the base and sides of the cell, diffusing into the vasa recta. Chloride ions move through leakage channels in the basolateral membrane into the interstitial fluid and then into the...