AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 3 719-R726, Copyright © 1991 by American Physiological Society
Contribution of renal medullary mitochondrial density to urinary concentrating ability in mammals
S. Abrahams, L. Greenwald and D. L. Stetson
Department of Zoology, Ohio State University, Columbus 43210.
In mammals, the length of the loops of Henle increases with increasing body
size without a concomitant rise in urinary concentrating ability. Because
mass-specific metabolic rate falls with increasing body mass, this study
sought to determine the extent to which this decline in metabolic rate
could explain the low urinary concentrating ability of large mammals with
long loops of Henle. Mitochondrial ultrastructural parameters were measured
in the medullary thick ascending limbs (mTALs) of a series of nine
mammalian genera ranging in body mass from 0.011 kg (bats) to approximately
400 kg (horses). The volume of mitochondria as a percent of mTAL cellular
volume declined with increasing body mass (Mb-0.056). Inner mitochondrial
membrane area per volume of mitochondrion also declined with increasing
body mass (Mb-0.034), as did basolateral membrane area per unit mTAL
cellular volume (Mb-0.075). Thus, not only do mitochondria occupy more
volume of mTAL cells of smaller mammals, but those mitochondria are also
more densely packed with cristae. Inner mitochondrial membrane area per
unit volume of mTAL cell cytoplasm scaled as Mb-0.092. The decline in inner
mitochondrial membrane area and basolateral membrane area per volume of
mTAL cell may explain at least in part the relationship between body mass
and renal concentrating ability in mammals of different sizes.
