التفاصيل البيبلوغرافية
| العنوان: |
A negative slope in the current-voltage relationship of the Na/K pump in Xenopus oocytes produced by reduction of external [K]. |
| المؤلفون: |
Rakowski, R., Vasilets, L., LaTona, J., Schwarz, W. |
| المصدر: |
Journal of Membrane Biology; 1991, Vol. 121 Issue 2, p177-187, 11p |
| مستخلص: |
To investigate the voltage dependence of the Na/K pump, current-voltage relations were determined in prophasearrested oocytes of Xenopus laevis. All solutions contained 5 mm Ba and 20 mm tetraethylammonium (TEA) to block K channels. If. in addition, the Na/K pump is blocked by ouabain, K-sensitive currents no larger than 50 nA/cm remain. Reductions in steady-state current (on the order of 700 nA/cm) produced by 50 μ m ouabain or dihydro-ouabain or by K removal, therefore, primarily represent current generated by the Na/K pump. In Na-free solution containing 5 mm K, Na/K pump current is relatively voltage independent over the potential range from −160 to +40 mV. If external [K] is reduced below 0.5 mm, negative slopes are observed over this entire voltage range. Similar results are seen in Na- and Ca-free solutions in the presence of 2 mm Ni, an experimental condition designed to prevent Na/Ca exchange. The occurrence of a negative slope can be explained by the voltage dependence of the apparent affinity for activation of the Na/K pump by external K, consistent with the existence of an external ion well for K binding. In 90 mm Na, 5 mm K solution, Na/K pump current-voltage curves at negative membrane potentials have a positive slope and can be described by a monotonically increasing sigmoidal function. At an extracellular [K] of 1.3 mm, a negative slope was observed at positive potentials. These findings suggest that in addition to a voltage-dependent step associated with Na translocation, a second voltage-dependent step that is dependent on external [K], possibly external K binding, participates in the overall reaction mechanism of the Na/K pump. [ABSTRACT FROM AUTHOR] |
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| قاعدة البيانات: |
Complementary Index |
