Sodium, bicarbonate, and chloride absorption by the proximal tubule

摘要: Proximal tubules are lined with epithelial cells that contain Na-K-ATPase in their basolateral cell membrane. The luminal membrane contains transport proteins couple movement of many solutes to the active sodium. connected by low-resistance junctional complexes permit passive via a paracellular shunt pathway. Acidification is mediated Na/H antiporter localized specifically and chloride-independent, voltage-dependent bicarbonate exit process rate acidification controlled pH peritubular fluids. Reabsorption NaCl from high-chloride, low-bicarbonate fluid late proximal tubule approximately 40% 60% active. In straight component entirely simple rheogenic sodium transport, chloride absorption driven through pathway lumen-negative PD. convoluted primarily neutral, both transported equivalent amounts cell. mechanisms for neutral across unknown. A reduction Starling forces (hydraulic oncotic pressures) suppresses net reabsorption two mechanisms: 1) increased permeability modest backleak (bicarbonate, glucose, amino acids) whose concentration falls below plasma level, 2) specific inhibition transcellular reduced protein some mechanism other than Na-K-ATPase.