ELECTRON MICROSCOPIC STUDIES ON THE SURFACE STRUCTURE OF EPITHELIUM OF THE URINARY BLADDER IN THE RICE-FIELD EEL, MONOPTERUS ALBUS(ZUIEW)

We provided already many evidences to proven that "degenerate gonad" in the Rice-field eel, Monopterus albus, is actually a large, tubular urinary bladder. At present, we researched the epithelium in the bladder of this fish in order to clear their surface ultrastructures of the epithelium and some morphological relationships between the structures and their relative cells. A range of the body weights of tested 20 fishes was 8.6-97.0g, and the range of their body lengths was 22.0- 49.0cm. The samples of the bladders of M. albus were drawn rapidly out from their body cavities, and were washed with 0.7% salt solution(4℃). The overturned samples were first prepared for scanning electron microscope(SEM; HITACHI S-450) and some of which were made into section ones with a sharp razor blade in order to observe a profile of the free surface of the bladder, and then were treated by routine methods for SEM. The samples for transmission electron microscope(TEM; JEM- l00CXⅡ) were treated by the methods mentioned in the our previous paper. The results by SEM showed that the inner surface of the bladder had many longitudinal plicae and grooves among the plicae(Plate Ⅰ: l), and a hexagonal,fingerprints-like structure consisted of many microridges(mean width was l25.2±25.6nm) was found on their surface(Plate Ⅰ: 2,3). These microridges were divided into two, a border ridge and a central ridge. The mean width of the channel between border ridges(a narrower pattern) was 143.0±70.3nm, and 236.5±83.9nm between central ridges(a wider pattern)(Plate Ⅰ: 3). The results scanned the section samples by SEM revealed that short finger-projecters at the free surface of superficial cell reported in the past paper were actually sections of the ridges observed presently(Plate Ⅰ: 4), certainly contained the border and central ridge. In addition, there existed some elliptic microholes between the border ridges(Plate Ⅰ: 3). The longer diameter of these microholes was 1.2μm, and the shorter was 0.7μm. Edge of the hole was smooth. However, we failed to find any inclusion inside the microholes. The results by TEM indicated that the cell conjunctions were situated beneath two short finger-projecters between which the interval was usually the narrower pattern, but not the wider pattern(Plate Ⅰ: 5). Therefore, the border ridge of the fingerprint-like structure was considered to be a boundary of superficial cell, and a fingerprint-like structure was surface outline of a superficial cell. Moreover, the stereo-appearance of such a superficial cell should be a flat hexagonal cell, bearing a fingerprint-like structure on its roof and many long finger-shape projecters on its base side. We also found that the microholes existing on the free surface of the bladder appeared to be a inverse speaker-shape in cross-section, and its depth was about 1 0μm and its diameter was about 1 5μm in bottom(Plate Ⅰ: 6). A pinenutbody-rich cell was found beneath a microhole. Such a cell comprised many pinenut-like bodies and many empty cavities, and either the pinenut-like body or the empty cavity contained a polycyclic structure respectively. As mentioned above, a most obvious characteristic of the surface ultrastructure in the bladder epithelium in M. albus is the fingerprint-like structure of roof of the superficial cell, which has been not reported in the current literatures concerning urinary bladders of the other animals. Although their function of the structures have not been explained correctly, but it is still possible that they can expand its superficial area of the superficial cell of the bladder epithelium and prolong accumulating time of urine at micro-surface of the cell so that can provide a certain condition for a matter transport of transmembrane.