Seasonal Change of Membrane Potential across the Proximal Tubular Epithelium in Bullfrog Kidneys

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Abstract
A micropuncture study was performed with K selective microelectrodes on the kidney of the bullfrog (Rana catesbeiana) in 2 different seasons: winter (7.degree. C) and summer (20.degree. C). The K activity in winter animals (7.degree. C) was 2.92 .+-. 0.33 (mean .+-. SD), 63.2 .+-. 12.7 and 2.68 .+-. 0.19 mM for the tubular fluid, cell and plasma, respectively, whereas that in summer animals (20.degree. C) was 2.84 .+-. 0.05, 61.8 .+-. 11.2 and 2.63 .+-. 0.24 mM, respectively, indicating no seasonal difference. The mean values of the membrane PD [potential difference] in winter animals were 59.4 .+-. 1.8 and 71.7 .+-. 7.2 mV for the luminal and peritubular borders, whereas those in summer animals were 55.1 .+-. 1.7 and 63.9 .+-. 6.9 mV, respectively, indicating that there was a significant seasonal difference (P < 0.05 and P < 0.001). Compared to winter animals, the changes in the electrochemical profile for K in summer animals were: the peritubular membrane PD was lower and the transtubular electrochemical gradient was less steep.

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