Cytochemical evidence for potassium‐dependent p‐nitrophenylphosphatase activity in pavement cells of Rana esculenta mesentery

Background We previously reported that during hibernation in Rana esculenta, various organs (i.e., skin, urinary bladder, kidney) change their osmoregulatory activity. Here, we considered the possible role of the frog mesentery in the ion transport, evaluating morphological and cytochemical (K+‐p‐nitrophenylphosphatase activity) aspects. Methods Pieces of mesentery from Rana esculenta collected in their natural environment during April, June, October, and January were processed to reveal ultrastructural morphology and K+‐p‐NPPase activity, using cerium as capture agent. Results The mesenteric mesothelium contained three types of cells: pavement, mitochondria‐rich, and ciliated. Only the pavement cells expressed intense reactivity on the basolateral membranes and in the adjacent pinocytotic vesicles; some reaction product also was found on the apical membranes. Moreover, morphological and cytochemical characteristics of the pavement cells appeared to be very seasonal. Conclusions The presence of mitochondria‐rich cells and ciliated cells, generally found in structures involved in the transport of liquids, as well as K+‐p‐NPPase activity and pinocytosis in pavement cells, is consistent with the hypothesis that frog mesentery may be involved in seasonally variable osmoregulation. Anat. Rec. 250:1–5, 1998. © 1998 Wiley‐Liss, Inc.