title: Role of Na+/Ca2+ exchange in transcellular Ca2+ transport across primary cultures of rabbit kidney collecting system.
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 omega 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+ (Nab+). Isoosmotic substitution of Nab+ 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 Cab2+ resulted in a significant increase in Ca2+ transport both in the presence and absence of Nab+. 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 microM) 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 Ca(2+)-ATPase, participate as well.
authors.affiliation: Department of Physiology, University of Nijmegen, The Netherlands.
authors.forename: R J
authors.initials: RJ
authors.lastname: Bindels
authors.forename: P L
authors.initials: PL
authors.lastname: Ramakers
authors.forename: J A
authors.initials: JA
authors.lastname: Dempster
authors.forename: A
authors.initials: A
authors.lastname: Hartog
authors.forename: C H
authors.initials: CH
authors.lastname: van Os
mesh_terms: D000042:Absorption; D000818:Animals; D015764:Bepridil / Q000494:pharmacology; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D004553:Electric Conductivity; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*
chemical_list: D015764:Bepridil; D012964:Sodium; D011188:Potassium; D002118:Calcium