Nuclear ion channel activity is regulated by actin filaments.
Prat, Adriana G., and Horacio F. Cantiello.
Renal Unit, Massachusetts General Hospital East, Charlestown,
Massachusetts, and Department of Medicine, Harvard Medical School,
Boston, Massachusetts
APStracts 2:0385C, 1995.
Actin filaments are novel second messengers involved in ion channel
regulation. Because cytoskeletal components interact with the nuclear
envelope, the actin cytoskeleton may also control nuclear membrane
function. In this report, the patch-clamp technique was applied to
isolated nuclei from amphibian A6 epithelial cells to assess the role
of actin filaments on nuclear ion channel activity under nucleus
-attached or excised conditions. The most prevalent spontaneous
nuclear ion channel species, 76% (n=46), was cation-selective and had
a maximal single channel conductance of approximately 420 pS. Nuclear
ion channels also displayed multiple subconductance states, including
channel activity of 26 pS which was frequently observed. Nuclear ion
channel activity on otherwise quiescent patches was induced by either
addition of the actin cytoskeleton disrupter cytochalasin D (CD, 5
[mu]g/ml, 60%, 3 out of 5 patches), or actin (10-1000 [mu]g/ml) to
the bathing solution of nucleus-attached patches (59%, 13 out of 22
patches). Actin also induced ion channel activity in quiescent
excised, inside-out patches from the nuclear envelope (80%, 4 out of
5 patches). In contrast, addition of bovine serum albumin (10-1000
[mu]g/ml) to the bathing solution of nucleus-attached patches was
without effect on nuclear ion channel activity (5 out of 5 patches).
The monoclonal antibody, MAb414, specific for nuclear pore complex
proteins, completely prevented either spontaneous or cytosolic actin
-induced nuclear ion channels under nucleus-attached conditions (4 out
of 4 patches), but not intranuclear actin-induced nuclear ion
channels under excised, inside-out conditions (3 out of 3 patches).
In nucleus-attached patches, channel activity was readily activated
by addition of the G-actin-binding protein DNAse I to nucleus
-attached patches (56%, 5 out of 9 patches), or further addition of
the actin-crosslinker filamin in the presence of actin (57%, 4 out of
7 patches). The data indicate that dynamic changes in actin filament
organization may represent a novel mechanism to control nuclear
function.
Received 6 July 1995; accepted in final form 19 October 1995.
APS Manuscript Number C405-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95