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The Journal of Experimental Biology 205, 897-904 (2002)
© 2002 The Company of Biologists Limited

K⁺ transport in the mesonephric collecting duct system of the toad Bufo bufo : microelectrode recordings from isolated and perfused tubules

Nadja Møbjerg^*, Erik Hviid Larsen and Ivana Novak

August Krogh Institute, Department of Zoophysiology, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark

^* Author for correspondence (e-mail: nmobjerg{at}aki.ku.dk )

Accepted 7 January 2001

We studied the mechanisms of K⁺ transport in cells from isolated and perfused collecting tubules and ducts from the mesonephric kidney of the toad Bufo bufo. Cells were impaled with microelectrodes across the basal cell membrane. The basolateral membrane potential (V_bl) depolarized upon change of bath [K⁺] from 3 to 20 mmol l^-1 demonstrating a large K⁺ conductance in this membrane. In collecting tubules and collecting ducts a V_bl of -66±2 mV and -74±4 mV depolarized by 30±2 mV and 36±3 mV, respectively (N=23; 15). The K⁺ channel inhibitor Ba²⁺ (1 mmol l^-1) inhibited the basolateral K⁺ conductance and depolarized a V_bl of -64±4 mV by 30±6 mV (N=8). Luminal K⁺ steps (3 to 20 mmol l^-1) demonstrated a K⁺ conductance in the apical cell membrane. In collecting tubules and collecting ducts a V_bl of -70±3 mV and -73±3 mV depolarized by 11±3 mV and 16±3 mV, respectively (N=11; 11). This conductance could also be inhibited by Ba²⁺, which depolarized a V_bl of -71±5 mV by 9±3 mV (N=5). The pump inhibitor ouabain (1 mmol l^-1) depolarized V_bl, but addition of furosemide to bath solution did not affect V_bl. The [K⁺] in urine varied from 1.3 to 22.8 mmol l^-1. In conclusion, we propose that the collecting duct system of B. bufo secretes K⁺ into the urine via luminal K⁺ channels.

Key words: amphibian, Ba²⁺, Bufo bufo, collecting duct, collecting tubule, K⁺ conductance, K⁺ secretion, kidney, mesonephros, ouabain, toad

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