Distal convoluted tubule

Physiology

It is partly responsible for the regulation of potassium, sodium, calcium, and pH.

On its apical surface (lumen side), cells of the DCT have a thiazide-sensitive Na-Cl cotransporter and are permeable to Ca, via the TRPV5 channel. On the basolateral surface (peritubular capillary side) there is an ATP-dependent Na/K antiporter pump, a secondary active Na/Ca transporter, and an ATP dependent Ca transporter. The basolateral ATP dependent Na/K pump produces the gradient for Na to be absorbed from the apical surface via the Na/Cl symporter, and for Ca to be reclaimed into the blood by the Na/Ca basolateral antiporter.

• It regulates pH by absorbing bicarbonate and secreting protons (H⁺) into the filtrate, or by absorbing protons and secreting bicarbonate into the filtrate.
• Sodium and potassium levels are controlled by secreting K⁺ and absorbing Na⁺. Sodium absorption by the distal tubule is mediated by the hormone aldosterone. Aldosterone increases sodium reabsorption. Sodium and chloride (salt) reabsorption is also mediated by a group of kinases called WNK kinases. There are 4 different WNK kinases, WNK1, WNK2, WNK3, and WNK4.
• It also participates in calcium regulation by reabsorbing Ca²⁺ in response to parathyroid hormone. PTH effect is mediated through phosphorylation of regulatory proteins and enhancing the synthesis of all transporters within the distal convoluted tubule.
• Arginine vasopressin receptor 2 is also expressed in the DCT.