Intracellular calcium plays an important role in the regulation of Cl- reabsorption in the ascending thin limb of Henle's loop (ATL). To elucidate the cytosolic Ca2+ dynamics in the ATL, intracellular Ca2+ concentration activity ([Ca2+](i)) was measured in the in vitro microperfused hamster ATL using fura 2. Basal [Ca2+](i) was 89.1 ± 7.3 nM (n = 9 tubules). Removal of Ca2+ from the peritubular solution decreased [Ca2+](i) from 89.1 ± 7.3 to 64.1 ± 7.1 nM in 2 min (n = 9, P < 0.05), whereas [Ca2+](i) did not change after removal of Ca2+ from the luminal solution. Addition of 1 mM NaCN to the bath increased [Ca2+](i). This effect was completely abolished by the elimination of ambient Ca2+. Trifluoperazine and N-(6-aminohexyl)- 5-chloro-1-naphthalenesulfonamide (W-7) in the bath reversibly increased [Ca2+](i), whereas addition of 1 mM ouabain to the bath decreased [Ca2+](i). Rates of changes in [Ca2+](i) after removal and replacement of basolateral Ca2+ were not affected by removal of Na+, K+, or Cl- from the bath, whereas nicardipine decreased these parameters. Increasing bath K+ from 5 to 100 mM decreased [Ca2+](i) from 69.3 ± 5.8 to 50.8 ± 5.0 nM in 1 min (n = 6, P < 0.05). Subsequent reduction of K+ from 100 to 5 mM increased [Ca2+](i) to 174.0 ± 30.8 nM in 1 min, followed by a gradual decrease in [Ca2+](i) to a steady-state level of 74.2 ± 8.0 nM in 2 min. Changes in basolateral K+ concentration did not affect [Ca2+](i) in the absence of ambient Ca2+. Nicardipine inhibited the changes in [Ca2+](i) after changes in bath K+ concentration. Addition of valinomycin to the bath increased [Ca2+](i) transiently. Changes in [Ca2+](i) by valinomycin were completely abolished in the absence of ambient Ca2+ or in the presence of nicardipine in the bath. These results suggest that ATL cells possess a calmodulin-sensitive Ca pump and a dihydropyridine-sensitive Ca2+ entry pathway in the basolateral membrane.
|ジャーナル||American Journal of Physiology - Renal Fluid and Electrolyte Physiology|
|出版ステータス||Published - 1995|
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