LENS MITOCHONDRIA IN THE RETINAL CONES OF THE TREE-SHREW TUPAIA-BELANGERI

In all mammals, the mitochondria of the cones of the retina are concen trated in the inner segment, Uniquely in tree-shrews (Tupaia, Scandent ia, Mammalia), a ''megamitochondrion'' exhibiting highly specialized s ystems of densely packed cristae and a very electron dense matrix, is located apically in the inner segment. The ellipsoid is a solid body c ontaining several megamitochondria and, towards its base, a large numb er of smaller mitochondria. The refractive index of isolated, but not oriented, inner segments of Tupaia belangeri is higher (x(A) = 1.405) than in any other mammal studied so far. The consistent geometrical pa ttern of the multilamellar crista-matrix systems, oriented longitudina lly towards the outer segment, suggests an additional optical function of the megamitochondria. Copyright (C) 1996 Elsevier Science Ltd