Transepithelial Potential in Mesonephric Nephrons of 7-day-old Chick Embryos in Relation to the Histochemically Detected Sodium Pump

Z. ZEMANOVÁ, E. UJEC

Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic

Received January 24, 2001
Accepted June 8, 2001

Summary
In order to obtain basic information on the transport properties of differentiating embryonic nephrons, we examined the 7-day-old chick mesonephros by measuring the transtubular epithelial potential difference (TPD) and by histochemical detection of Na,K-ATPase activity. TPD as an indicator of the electrogenic transport was measured in individual segments of superficial nephrons in vivo. Their electric polarity was always lumen-negative. TPD was reduced by addition of 10 mM KCN applied to the mesonephric nephrons from the outside. In the proximal tubules, TPD was significantly lower (mean±SD: -1.0±0.5 mV) than in the distal and collecting tubules (-2.2±1.0 mV, pŁ0.05). Activity of the sodium pump was evaluated histochemically by detection of ouabain-sensitive potassium-dependent p-nitrophenyl phosphatase in cryostat sections of the mesonephros. The enzyme activity was demonstrated only in distal tubules and in the collecting ducts, but not in the proximal tubules. These findings have revealed significant differences between embryonic nephron segments: the distal tubule, in contrast to the proximal one, is supplied by the sodium pump and is able to generate higher TPD. Therefore, we consider that it is only the distal nephron, which possesses the ability of active transport.

Key words
Chick embryonic kidney · Tubular segments · Transepithelial potential difference · Ouabain-sensitive K+-NPPase · Active transport

Reprint requests
Z. Zemanová, M.D., Institute of Physiology, Academy of Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague 4, Czech Republic, Telephone 0420-2-4752449, fax 0420-2-4752488, e-mail: zemanova@biomed.cas.cz