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1
/ mice
Department of Physiology and Biophysics, University of Nebraska Medical Center, Omaha, Nebraska 68198-4575
Large-conductance
Ca2+-activated K+ channels (BKCa)
are composed of pore-forming 
-subunits and one of four accessory
-subunits. The 1-subunit, found predominantly in smooth muscle,
modulates the Ca2+ sensitivity and pharmacological
properties of BKCa. BKCa-1 null mice
(M1
/) are moderately hypertensive, consistent with
the role of BKCa in modulating intrinsic vascular tone.
Because BKCa are present in various renal cells including
the mesangium and cortical collecting ducts, we determined whether
fluid or electrolyte excretion was impaired in M1/
under euvolemic, volume-expanded, or high-salt diet conditions. Under
euvolemic conditions, no differences in renal function were found
between M1/ and M1+/+. However,
glomerular filtration rate (GFR) and fractional K+
excretion were significantly impaired in M1/ in
response to acute volume expansion. In contrast, M1/
exhibited enhanced Na+ excretion and fractional
Na+ excretion responses to acute volume expansion.
Differences in renal function between M1+/+ and
M1/ were not observed when chronically treated with
a high-salt diet. These observations indicate that the 1-subunit of
BKCa contributes to the increased GFR that accompanies an
acute salt and volume load and raises the possibility that it is also
involved in regulating K+ excretion under these conditions.
large-conductance, calcium-activated potassium channels; maxi K channel; glomerular filtration rate; volume expansion; potassium excretion
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