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Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520-8026
It has been well documented
that low concentrations of ANG II (10
11 to
10
10 M) stimulate, whereas high concentrations of ANG II
(10
8 to 10
5 M) inhibit Na+
transport in proximal tubules of rat and rabbit kidneys. Measured ANG
II concentration in proximal tubular fluid is in the nanomolar range.
In the present study, we investigated the role of PKC, intracellular
Ca2+, and cAMP in modulating the effects of luminal ANG II
on Na+ absorption by microperfusion techniques in rabbit
superficial segment of proximal tubules in vitro. We confirmed that ANG
II (10
9 M) had no change on fluid absorption
(Jv); however, fluid absorption increased
significantly when 10
9 M ANG II and
3,4,5-trimethoxybenzoic acid-8-(diethylamino)octyl ester (TMB-8), a
blocker of intracellular calcium mobilization, were added together. In
contrast, ANG II significantly decreased Jv when
PKC was inhibited. When 10
9 M ANG II was present together
with 1-(5-isoquinolinesulfonyl)-2-mehtylpiperazine and TMB-8, no
significant change of Jv occurred. Inhibition of endogenous cAMP activity by a PKA inhibitor did not change either basal
or ANG II-stimulated fluid absorption. Our results indicate that ANG II
regulates Na+ absorption by a cAMP-independent mechanism
and that PKC and intracellular calcium both play a critical role in
modulating the effects of physiological concentration of ANG II on
proximal tubule transport. Balance between these two cytosolic
messengers modulates the effects of ANG II on fluid absorption in the
proximal tubule.
Na+ transport; proximal tubule; microperfusion
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