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AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge.

1. The whole-cell recording mode of the patch-clamp technique was used to investigate the ionic currents of enterocytes isolated from the small intestine epithelium of Necturus maculosus. 2. When enterocytes were bathed in a physiological Ringer solution and dialysed with a K(+)-rich intracellular solution containing 1.5 x 10(-7) M intracellular Ca2+, strongly outwardly rectifying currents were observed. These currents were absent from enterocytes internally dialysed with K(+)-free solutions. 3. The kinetics of activation of the outwardly rectifying current was monoexponential with rate constants decreasing with depolarization from 160 ms at 20 mV to 40 ms at 60 mV. Similar voltage dependence of the relaxations after activation were observed. 4. Strongly buffering intracellular Ca2+ with EGTA inhibited outward currents, while increasing Ca2+ increased both their magnitude and rate of activation. 5. Bath application of the K+ channel inhibitors Ba2+ and TEA greatly attenuated outwardly rectifying currents. This observation plus the fact that tail currents reverse near EK points to K+ as the charge carrier in these currents. 6. Outside-out patches showed maxi K+ channels and lower conductance K+ channels. Averaging fluctuations of the maxi K+ channels gave a kinetic behaviour similar to the whole-cell currents.

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