Functional evidence for a ca2+/polyvalent cation-sensor in the
mouse thick ascending limb.
Paulais, Marc, Maryvonne Baudouin-Legros, and Jacques Teulon.
Institut National de la Sant[theta] et de la Recherche
M[theta]dicale Unit[theta] 323, Facult[theta] de M[theta]decine
Necker, Paris, France
APStracts 3:0143F, 1996.
The effects of extracellular polyvalent cations on the cytosolic free
Ca2+ concentration ([Ca2+]i) of isolated segments of the mouse
nephron were investigated using fura-2 microfluorometry.
Extracellular Ca2+ concentration ([Ca2+]o), gadolinium (Gd3+) and
neomycin (Neo) increased the [Ca2+]i in CTAL tubules with effective
doses (ED50) of 3.5 mM for Ca2+, 20 M for Gd3+and 40 M for Neo. This
effect was reproduced by Ba2+, but not by Mg2+. High [Ca2+]o
inhibited the responses to Gd3+, Neo and Ba2+. The Gd3+- and Neo
-evoked [Ca2+]i transients persisted in the absence of external Ca2+
and were abolished by the depletion of internal Ca2+ stores with
thapsigargin (TG). The responses to rises in [Ca2+]owere similarly
inhibited by TG, and slightly reduced by 20 M La3+ but not by 10 M
nifedipine. Mn2+ also mobilized a TG-sensitive internal Ca2+ store,
and stimulated its own entry. External Ca2+, Gd3+ and Neo induced
small but significant increases in [Ca2+]i in DCT, CCD and OMCD
segments, transiently increased [Ca2+]i in some MTAL tubules, but had
no effect on DTL. We conclude that a Ca2+-mobilizing Ca2+/polyvalent
cation-sensor resembling that of the parathyroid gland cells is
predominantly located in the mouse CTAL, but also in the MTAL and, to
a lower extent, in more distal segments.
Received 21 February 1996; accepted in final form 2 August 1996.
APS Manuscript Number F55-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996