Cytosolic ca2+ dynamics in hamster ascending thin limb of henle's loop.
Takahashi, Nobuyuki, Yoshiaki Kondo, Osamu Ito, Yutaka Igarashi, Ken Omata,
and Keishi Abe.
Department of Clinical Biology and Hormonal Regulation, Department of
Pediatrics, and The Second Department of Internal Medicine, Tohoku University
School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-77, JAPAN.
APStracts 2:0003F, 1995.
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 calcium 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). Removal of Ca2+ from the
peritubular solution decreased [Ca2+]i from 89.1 +/- 7.3 nM to 64.1 +/- 7.1
nM in 2 min (n=9, p<.05), while [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 W7 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 mM to 100 mM decreased [Ca2+]i from 69.3 +/- 5.8 nM to 50.8 +/- 5.0 n in
1 min (n=6, p<.05). Subsequent reduction of K+ from 100 mM 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.
Received 17 October 1994; accepted in final form 17 January 1995.
APS Manuscript Number F0371-4.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 February 1995.