Na+ Channels as Molecular Substrate of Cardiac Excitability: Elementary Properties and Responsiveness to Drugs

1993 ◽  
pp. 222-233
Author(s):  
M. Kohlhardt
Keyword(s):  
Na Channels ◽  
Cardiac Excitability

scholarly journals Gating of Na channels in the rat cortical collecting tubule: effects of voltage and membrane stretch.

1996 ◽  
Vol 107 (1) ◽  
pp. 35-45 ◽  
Author(s):  
L G Palmer ◽  
G Frindt
Keyword(s):  
Voltage Dependence ◽  
Single Channel ◽  
Apical Membrane ◽  
Na Channels ◽  
Patch Clamp Technique ◽  
Open Time ◽  
Collecting Tubule ◽  
Excised Patches ◽  
The Mean ◽  
Cortical Collecting Tubule

The gating kinetics of apical membrane Na channels in the rat cortical collecting tubule were assessed in cell-attached and inside-out excised patches from split-open tubules using the patch-clamp technique. In patches containing a single channel the open probability (Po) was variable, ranging from 0.05 to 0.9. The average Po was 0.5. However, the individual values were not distributed normally, but were mainly < or = 0.25 or > or = 0.75. Mean open times and mean closed times were correlated directly and inversely, respectively, with Po. In patches where a sufficient number of events could be recorded, two time constants were required to describe the open-time and closed-time distributions. In most patches in which basal Po was < 0.3 the channels could be activated by hyperpolarization of the apical membrane. In five such patches containing a single channel hyperpolarization by 40 mV increased Po by 10-fold, from 0.055 +/- 0.023 to 0.58 +/- 0.07. This change reflected an increase in the mean open time of the channels from 52 +/- 17 to 494 +/- 175 ms and a decrease in the mean closed time from 1,940 +/- 350 to 336 +/- 100 ms. These responses, however, could not be described by a simple voltage dependence of the opening and closing rates. In many cases significant delays in both the activation by hyperpolarization and deactivation by depolarization were observed. These delays ranged from several seconds to several tens of seconds. Similar effects of voltage were seen in cell-attached and excised patches, arguing against a voltage-dependent chemical modification of the channel, such as a phosphorylation. Rather, the channels appeared to switch between gating modes. These switches could be spontaneous but were strongly influenced by changes in membrane voltage. Voltage dependence of channel gating was also observed under whole-cell clamp conditions. To see if mechanical perturbations could also influence channel kinetics or gating mode, negative pressures of 10-60 mm Hg were applied to the patch pipette. In most cases (15 out of 22), this maneuver had no significant effect on channel behavior. In 6 out of 22 patches, however, there was a rapid and reversible increase in Po when the pressure was applied. In one patch, there was a reversible decrease. While no consistent effects of pressure could be documented, membrane deformation could contribute to the variation in Po under some conditions.

Whole cell and unitary amiloride-sensitive sodium currents in M-1 mouse cortical collecting duct cells

1996 ◽  
Vol 270 (4) ◽  
pp. C998-C1010 ◽  
Author(s):  
M. L. Chalfant ◽  
T. G. O'Brien ◽  
M. M. Civan
Keyword(s):  
Collecting Duct ◽  
Cell Permeability ◽  
Na Channel ◽  
Na Channels ◽  
Cortical Collecting Duct ◽  
Ionic Selectivity ◽  
Whole Cell ◽  
Duct Cells ◽  
Excised Patches ◽  
Collecting Duct Cells

Amiloride-sensitive whole cell currents have been reported in M-1 mouse cortical collecting duct cells (Korbmacher et al., J. Gen. Physiol. 102: 761-793, 1993). We have confirmed that amiloride inhibits the whole cell currents but not necessarily the measured whole cell currents. Anomalous responses were eliminated by removing external Na+ and/or introducing paraepithelial shunts. The amiloride-sensitive whole cell currents displayed Goldman rectification. The ionic selectivity sequence of the amiloride-sensitive conductance was Li+ > Na+ >> K+. Growth of M-1 cells on permeable supports increased the amiloride-sensitive whole cell permeability, compared with cells grown on plastic. Single amiloride-sensitive channels were observed, which conformed to the highly selective low-conductance amiloride-sensitive class [Na(5)] of epithelial Na+ channels. Hypotonic pretreatment markedly slowed run-down of channel activity. The gating of the M-1 Na+ channel in excised patches was complex. Open- and closed-state dwell-time distributions from patches that display one operative channel were best described with two or more exponential terms each. We conclude that 1) study of M-1 whole cell Na+ currents is facilitated by reducing the transepithelial potential to zero, 2) these M-1 currents reflect the operation of Na(5) channels, and 3) the Na+ channels display complex kinetics, involving > or = 2 open and > or = 2 closed states.

Differences in open state of NBA-modified cardiac Na+ channels

1988 ◽  
Vol 15 (5) ◽  
pp. 289-292 ◽  
Author(s):  
M. Kohlhardt ◽  
H. Fichtner ◽  
U. Fröbe
Keyword(s):  
Na Channels

scholarly journals Saturation behavior of single, amiloride-sensitive Na+ channels in planar lipid bilayers

1984 ◽  
Vol 46 (6) ◽  
pp. 831-835 ◽  
Author(s):  
L. Olans ◽  
S. Sariban-Sohraby ◽  
D.J. Benos
Keyword(s):  
Lipid Bilayers ◽  
Planar Lipid Bilayers ◽  
Na Channels
Sign in / Sign up

Export Citation Format

Share Document