Sodium-dependent potassium channels in leech P neurons.
In leech P neurons the inhibition of the Na(+)-K(+) pump by ouabain or omission of bath K(+) leaves the membrane potential unaffected for a prolonged period or even induces a marked membrane hyperpolarization, although the concentration gradients for K(+) and Na(+) are attenuated substantially. As shown previously, this stabilization of the membrane potential is caused by an increase in the K(+) conductance of the plasma membrane, which compensates for the reduction of the K(+) gradient. The data presented here strongly suggest that the increased K(+) conductance is due to Na(+)-activated K(+) (K(Na)) channels. Specifically, an increase in the cytosolic Na(+) concentration ([Na(+)](i)) was paralleled by a membrane hyperpolarization, a decrease in the input resistance (R(in)) of the cells, and by the occurrence of an outwardly directed membrane current. The relationship between R(in) and [Na(+)](i) followed a simple model in which the R(in) decrease was attributed to K(+) channels that are activated by the binding of three Na(+) ions, with half-maximal activation at [Na(+)](i) between 45 and 70 mM. At maximum channel activation, R(in) was reduced by more than 90%, suggesting a significant contribution of the K(Na) channels to the physiological functioning of the cells, although evidence for such a contribution is still lacking. Injection experiments showed that the K(Na) channels in leech P neurons are also activated by Li(+).
Klees
G
G
Institut für Neurobiologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Düsseldorf 40225, Germany.
Hochstrate
P
P
Dierkes
P W
PW
D000818:Animals; D003600:Cytosol / Q000378:metabolism; D004566:Electrodes; D004594:Electrophysiology; D047709:Hirudo medicinalis / Q000201:enzymology / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000201:enzymology* / Q000502:physiology; D011188:Potassium / Q000378:metabolism* / Q000502:physiology; D012964:Sodium / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000502:physiology*
D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium