Format

Send to

Choose Destination
See comment in PubMed Commons below
J Gen Physiol. 1972 Nov;60(5):588-608.

Negative conductance caused by entry of sodium and cesium ions into the potassium channels of squid axons.

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.

PMID:
4644327
PMCID:
PMC2226091
[Indexed for MEDLINE]
Free PMC Article
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for HighWire Icon for PubMed Central
    Loading ...
    Support Center