Transport Processes, Metabolism and Endocrinology; Kidney, Gastrointestinal Tract, and Exocrine Glands

Pflügers Archiv

, Volume 420, Issue 5, pp 566-572

Role of Na+/Ca2+ exchange in transcellular Ca2+ transport across primary cultures of rabbit kidney collecting system

  • R. J. M. BindelsAffiliated withDepartment of Physiology, University of Nijmegen
  • , P. L. M. RamakersAffiliated withDepartment of Physiology, University of Nijmegen
  • , J. A. DempsterAffiliated withDepartment of Physiology, University of Nijmegen
  • , A. HartogAffiliated withDepartment of Physiology, University of Nijmegen
  • , C. H. van OsAffiliated withDepartment of Physiology, University of Nijmegen

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Abstract

Cells from connecting tubule and cortical collecting duct of rabbit kidney were isolated by immunodissection with mAb R2G9 and cultured on permeable filters. Confluent monolayers developed an amiloride-sensitive transepithelial potential difference of −50±1 mV (lumen negative) and a transepithelial resistance of 507±18 Ω cm2. Transepithelial Ca2+ transport increased dose-dependently with apical [Ca2+] and, in solutions containing 1 mM Ca2+, the active transcellular Ca2+ transport rate was 92±2 nmol h−1 cm−2. Transcellular Ca2+ transport was dependent on basolateral Na+ (Na b + ). Isoosmotic substitution of Na b + for N-methylglucamine resulted in a concentration-dependent decrease in Ca2+ absorption, with maximal inhibition of 67±5%. A Hill plot of the Na+-dependence yielded a coefficient of 1.9±0.4, indicating more than one Na+ site on a Na+-dependent Ca2+ transport system. In addition, the absence of Ca b 2+ resulted in a significant increase in Ca2+ transport both in the presence and absence of Na b + . Added basolaterally, ouabain (0.1 mM) inhibited Ca2+ transport to the same extent as did Na+-free solutions, while bepridil (0.1 mM), an inhibitor of Na+/Ca2+ exchange, reduced Ca2+ transport by 32±6%. Methoxyverapamil, felodipine, flunarizine and diltiazem (10 μM) were without effect. Depolarisation of the basolateral membrane, by raising [K+]b to 60 mM, significantly decreased transcellular Ca2+ transport, which is indicative of electrogenic Na+/Ca2+ exchange. In conclusion, active Ca2+ transport in the collecting system of rabbit kidney is largely driven by basolateral Na+/Ca2+ exchange. However, a residual Ca2+ absorption of about 30% was always observed, suggesting that other Ca2+ transport mechanisms, presumably a Ca2+-ATPase, participate as well.

Key words

Na+/Ca2+ exchange Rabbit kidney Connecting tubule Cortical collecting duct Ca2+ reabsorption Bepridil Ca2+ entry blockers Ca2+ transport