Urea transport in frog oocytes: effect of osmotic stress and vasopressin.
The transport of water and urea across biological membranes are considered to traverse separate channels or pores. While vasopressin responsiveness correlates with increased urea/water permeability in some epithelia, oocytes provide a single cell system to determine the coupling relationship. Urea transport under isotonic and hypotonic conditions are determined in full-grown frog oocytes in follicles. We found that urea reached equilibrium distribution (ratio of 14C-urea concentrations inside and outside of the oocyte) rapidly and remained equilibrated over 20 h period, independent of external urea concentrations. Thus, urea uptake is not via an active transport system. While hypotonicity caused oocytes to swell, vasopressin did not exert additional effect. Under hypotonic conditions, distribution ratios of water and urea changed in different ways supporting the view that distinguishable channels (pathways) were involved. It appeared that no correlated changes due to vasopressin occurred under osmotic challenge. The response pattern to vasopressin was different between renal epithelia and frog oocyte.
Reynhout
J K
JK
Department of Physiology, Chang Gung College of Medicine and Technology, Tao-Yuan, Taiwan, R.O.C.
Horowitz
S B
SB
Lau
Y T
YT
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D005260:Female; D009865:Oocytes / Q000378:metabolism*; D009997:Osmotic Pressure; D011894:Rana pipiens; D014508:Urea / Q000378:metabolism*; D014667:Vasopressins / Q000494:pharmacology*
D014667:Vasopressins; D014508:Urea