J. Lombardi et T. Files, EGG CAPSULE STRUCTURE AND PERMEABILITY IN THE VIVIPAROUS SHARK, MUSTELUS-CANIS, The Journal of experimental zoology, 267(1), 1993, pp. 76-85
The structure and permeability characteristics of egg capsules of the
viviparous matrotrophic elasmobranch Mustelus canis were investigated
by scanning electron microscopy (SEM), X-ray microprobe elemental anal
ysis, and through the use of modified Ussing chambers. The egg capsule
surrounds the developing embryo during gestation and consists of a fo
ur or more orthogonally arranged laminae of fibrous material. SEM and
energy dispersive spectroscopy (EDS) of inner and outer capsular surfa
ces reveal that the capsule is 4.7 mum in thickness and possesses scat
tered calcium deposits along its inner and outer surfaces. Transcapsul
ar permeability studies qualitatively demonstrate that capsules are re
adily permeable to fast green fcf (808 Da) and rose bengal (1,000 Da).
Capsules are impermeable to insulin (5,750 Da), lysozyme (14,300 Da)
and bovine albumin (66,000 Da). Glucose (P = 3.3 x 10(-4) +/- 1.2 x 10
(-4) cm/sec [n = 120]) and urea (P = 4.5 x 10(-4) +/- 2.3 x 10(-4) cm/
sec [n = 139]) readily pass across the egg capsules. It is suggested t
hat maternal-embryonic nutrient transfer primarily involves the transc
apsular passage of low (<5 kDa) molecular weight components. These dat
a are discussed in relation to the mechanisms of placental attachment
in matrotrophic sharks. (C) 1993 Wiley-Liss. Inc.