Ip3-activated ca2+ channels in the plasma membrane of cultured
vascular endothelial cells.
L, Vaca, and Kunze Dl.
Department of Molecular Physiology and Biophysics, Baylor College
of Medicine, Houston, Texas 77030
APStracts 2:0183C, 1995.
Although it is clear that IP3 plays an important role in the
activation of Ca2+ influx, the mechanisms by which this occurs remain
controversial. In an attempt to determine the role of IP3 in the
activation of Ca2+ influx, patch clamp single channel experiments in
the cell-attached, inside-out and outside-out configurations were
performed on cultured bovine aortic endothelial cells (BAEC). The
results presented here indicate that both IP3 and intracellular Ca2+
can modulate the activity of a Ca2+ selective channel found in the
plasma membrane of these cells. Addition of 10 M inositol-1,4,5
-trisphosphate (IP3) increased channel Po from a control value of 0.12
0.05 to 0.7 0.13 at a constant intracellular Ca2+ of 1 nM in excised
inside-out patches. Inositol-1,3,4,5-tetraphosphate (IP4) at 50 M was
ineffective in altering channel Po. Channel activity declined after
approximately 2 minutes in the continuous presence of IP3. 3-4
minutes after addition of IP3 channel Po was reduced from 0.7 0.2 to
0.2 0.1, indicating that an additional regulator might be required to
maintain channel activity in excised patches. The channel was
reversibly blocked by application of 1 g/ml heparin to the
intracellular side of inside-out patches. This Ca2+ selective channel
is indistinguishable from the depletion-activated Ca2+ channel we
have previously described in BAEC.
Received 9 January 1995; accepted in final form 7 April 1995.
APS Manuscript Number C18-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 9 May 1995.