title: Active Ca2+ reabsorption in the proximal tubule of the rat kidney. Dependence on sodium- and buffer transport.
abstract: Using the stop flow microperfusion technique with simultaneous capillary perfusion the rate active Ca2+ reabsorption was evaluated by measuring the static head electrochemical potential difference as well as the permeability of the tubular wall for Ca2+ ions. Under control conditions the active Ca2+ transport was calculated to be 3.35 X 10(-13) mol/cm - s. It declined toward zero if the ambient Na+ was replaced by choline or lithium. Parallel experiments in the golden hamster showed that active Ca2+ transport, vanished completely if active Na+ transport was blocked by ouabain (1 mM). These data indicate that the active Ca2+ reabsorption from the proximal tubule depends on the active reabsorption of Na2+ presumably via a Na+-Ca2+ countertransport at the contraluminal cell membrane. The static head electrochemical potential difference of Ca2+ is the same in late and early proximal tubules. It is also not affected by the presence of acetazolamide (10(-4) M) by the absence of bicarbonate or glycodiazine buffer or by the absence or presence of phosphate (2 mM).
mesh_terms: D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001693:Biological Transport, Active; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability; D002794:Choline / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D002021:Buffers; D010042:Ouabain; D008094:Lithium; D012964:Sodium; D002794:Choline; D000086:Acetazolamide; D002118:Calcium