Cortical collecting tubule, transport

Amiloride and triamterene-Am or 6e and triamterene not only inhibit sodium reabsorption induced by aldosterone, but they also inhibit basal sodium reabsorption. They are not aldosterone antagonists, but act directly on the renal distal tubule, cortical collecting tubule and collecting duct. They induce a reversal of polarity of the transtubular electrical-potential difference and inhibit active transport of sodium and potassium. Amiloride may inhibit sodium, potassium-ATPase. 

Cortical collecting tubule (CCT) Na+ reabsorption (2-5%) coupled to K+ and H+ secretion Variable2 Na channels (ENaC), channels,1 H transporter,1 aquaporins K+-sparing diuretics... 

Stoner LC, Burg MB, Orloff J (1974) Ion transport in cortical collecting tubule effect of amiloride. Am J Physiol 227 453 159... 

Jacobson, H.R., S. Corona, J.H. Capdevila, N. Chacos, S. Manna, A. Womack et al. (1984). Effects of epoxyeicosatrienoic acids on ion transport in the rabbit cortical collecting tubule. In P. Braquet, J.C. Frolich, S. Nicosia, and R. Garay (eds). Prostaglandins and Membrane Ion Transport. Raven Press, New York, p. 311. 

Holt, W.F. and Lechene, C. (1981). ADH-PGE2 interactions in cortical collecting tubule. I. Depression of sodium transport. Am. ]. Physiol, 241, F452-460... 

A nephron, showing the major sites and percentage (in braces) of sodium absorption along with other features of solute transport. The filtered load = GFR (180 L/day) Xplasma Na+ (140 mEq/L) or 25,200 mEq/day. About 1% of this amount is excreted in voided urine. Sites where tubular fluid is isosmotic, hypertonic, or hypotonic relative to plasma are shown. POT, proximal convoluted tubule LH, loop of Henle DOT, distal convoluted tubule CCD, cortical collecting duct TAL, thick ascending loop. 

In addition to their effects on distal Na+ and K+ transport, all of the K -sparing diuretics inhibit urinary H secretion by the late distal tubule and cortical collecting duct The mechanism of this inhibitory action is not totally clear. 

The effectiveness of thiazide and loop diuretics is dependent on the concentration of the drug in the tubular lumen. Diuretics are delivered to the tubular lumen of the kidney by active transport by the proximal mbular cells. Osmotic diuretics, on the other hand, are freely filtered into the mbular lumen in the proximal tubule, whereas spironolactone gains access to mineralocorticoid receptors in the cortical collecting duct through diffusion from the systemic circulation. 

---