Overview of Ion Movements in the Kidney


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A summary of small molecule movements across apical and basolateral membranes in different parts of the kidney.

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Overview of Ion Movements in the Kidney

  1. 1. Kidney  Apical Basolateral Tubular fluid OUT  IN Tubular wall cell  IN  OUT Function segment Membrane MembranePCT (early) CO2 production via Na+ SGLT Glu CO2 + H2O ↔ H+ + 2 K+ Na+/K+ pump Na+ - reabs of 70% of NaCl carbonic anhydrase H+ NHE Na+ HCO3- GLUT2 Glu - reabs of 100% of glucose (CO2 has diffused in) Various HCO3- HCO3- movement of ions creates osmotic transporters gradient for water absorptionPCT (late) CO2 production via SGLT-1 2 Na+ 2 K+ Na+/K+ pump 3 Na+ - now against greater gradient carbonic anhydrase Glu GLUT 1 Glu - more Cl- abs. than in earlier part KCC K+, Cl- - movement of ions creates osmotic H+ NHE: Na+ gradient for water absorption - Cl channels Cl-PCT Na+ 2 K+ Na+/K+ pump* 3 Na+ - reabs of K+ anions KCC K+ Cl- - largely paracellularly (passive) - *K+ held particularly low between proximal tubule cells, more pumpsPCT NH3 diffuses out to H+ NHE3 Gln ↔ NH4+ + α-KG 2 K+ Na+/K+ pump 3 Na+ - Production of HCO3- be converted to NH4+ α-KG ↔ 2 HCO3- NBC-1 Na+ - If necessary NH4+ ↔ NH3 + H + 3HCO3- - NH3/ NH4+ Cl- BC HCO3-PCT CO2 production via H+ ATP-pump CO2 + H2O ↔ H+ + 2 K+ Na+/K+ pump 3 Na+ - Reabsorption of 80 % of HCO3-thick LOH carbonic anhydrase H+ NHE3 Na + HCO3- NBC-1 Na+ (CO2 has diffused in) 3HCO3- Cl- BC HCO3- + + -thick LOH NKCC2 Na K 2Cl 2 K+ Na+/K+ pump 3 Na+ - reabs of K+ K+ K+ channel Cl- channel Cl- - trans- and paracellularly K+ channel K+thick LOH NH4+ from PCT NKCC2 Na+NH4+2Cl- NH4+ ↔ NH3 + H+ NH3 - NH3 diffuses to medullary interstit.DCT CO2 production via H+ ATP-pump K+ Type A intercalated cells: Cl- BC HCO3- - Reabsorption of HCO3-auseCD carbonic anhydrase H+ ATP-pump CO2 + H2O ↔ H+ + Cl- channel Cl- - Cl- recycles HCO3- (CO2 has diffused in)DCT H+ ATP-pump K+ K+ channel K+ - reabs of K+CDDCT ENaC Na+ Principal cell: Aldosterone 2 K+ Na+/K+ pump 3 Na+ - K+ regulation +CD K SK initiates gene expression K+ channel K+ - K+ from blood to tubular fluid!! of membrane proteins - Excretion if necessaryDCT TRPV5 Ca2+ Ca2+ binds calbindin to 2 K+ Na+/K+ pump 3 Na+ - Ca2+ regulationCD TRPV6 Ca2+ cross the cells ATP-pump Ca2+ - Na+ cycles K+ K+ channel 3 Na+ NCX Ca2+CD H+ ATP-pump K + CO2 + H2O ↔ H + + - H+ pumped to tubular fluid to H+ ATP-pump HCO3- retain NH3 as NH4+ (CO2 has diffused in)CD NH3 trapped as NH4+ - NH3 diffuses from medulla to CDMedulla/ NKCC2 Na+K+2Cl- 2 K+ Na+/K+ pump 3 Na+ - Make medulla hypertonicthick channels K+ Cl- - K+ recyclesLOH K+ K+ channel (interstitium!) - less blood vessels!!!GLUT1: passive? Also takes up Vit C GLUT2: passive glucose transporter (GLUT4: insulin regulated glucose transporter, not shown here)SGLT: sodium glucose transporter (2* active) NHE: sodium hydrogen exchanger (2*) KCC: potassium chlorine co-transporter (2*)NKCC2: sodium potassium 2 chloride cotransporter ENaC: epithelial sodium channel SK: small Ca2+ activated K+ channelNBC-1: Sodium-bicarbonate cotransporter NCX: Sodium calcium exchanger BC: Bicarbonate-chloride cotransporter (named so by me)PCT/DCT: proximal / distal convoluted tubule LOH: loop of Henle CD: collecting duct