Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 60 (5), 588-608

Negative Conductance Caused by Entry of Sodium and Cesium Ions Into the Potassium Channels of Squid Axons

Negative Conductance Caused by Entry of Sodium and Cesium Ions Into the Potassium Channels of Squid Axons

F Bezanilla et al. J Gen Physiol.

Abstract

Internal Cs(+), Na(+), Li(+), and, to a lesser degree, Rb(+) interfere with outward current through the K pores in voltage clamped squid axons. Addition of 100 mM NaF to the perfusion medium cuts outward current for large depolarizations about in half, and causes negative conductance over a range of membrane voltages. For example, suddenly reducing membrane potential from +100 to +60 mv increases the magnitude of the outward current. Internal Cs(+) and, to a small extent, Li(+), also cause negative conductance. Na(+) ions permeate at least 17 times less well through the K pores than K(+), and Cs(+) does not permeate measurably. The results strongly suggest that K pores have a wide and not very selective inner mouth, which accepts K(+), Na(+), Li(+), Cs(+), tetraethylammonium ion (TEA(+)), and other ions. The diameter of the mouth must be at least 8 A, which is the diameter of a TEA(+) ion. K(+) ions in the mouths probably have full hydration shells. The remainder of the pore is postulated to be 2.6-3.0 A in diameter, large enough for K(+) and Rb(+) but too small for Cs(+) and TEA(+). We postulate that Na(+) ions do not enter the narrower part of the pore because they are too small to fit well in the coordination cages provided by the pore as replacements for the water molecules surrounding an ion.

Similar articles

See all similar articles

Cited by 267 articles

See all "Cited by" articles

References

    1. J Gen Physiol. 1966 Nov;50(2):279-93 - PubMed
    1. J Physiol. 1965 Oct;180(4):788-820 - PubMed
    1. Proc Natl Acad Sci U S A. 1967 May;57(5):1350-5 - PubMed
    1. J Physiol. 1967 Nov;193(2):433-42 - PubMed
    1. J Gen Physiol. 1968 May;51(5):Suppl:102S+ - PubMed
Feedback