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Biophys J, July 2001, p. 117-124, Vol. 81, No. 1
and
*Department of Pathology and Cell Biology, Thomas Jefferson
University, Philadelphia, Pennsylvania 19103 USA; and
Department of Physiology, University of Pennsylvania,
Philadelphia, Pennsylvania 19104 USA
Inositol 1,4,5-trisphosphate (InsP3)
receptors (InsP3Rs) are intracellular Ca2+
channels gated by the second messenger InsP3. Here we
describe a novel approach for recording single-channel currents through recombinant InsP3Rs in mammalian cells that applies
patch-clamp electrophysiology to nuclei isolated from COS-7 cells
transiently transfected with the neuronal (SII(+)) and peripheral
(SII(
)) alternatively-spliced variants of the rat type 1 InsP3R. Single channels that were activated by
InsP3 and inhibited by heparin were observed in 45% of
patches from nuclei prepared from transfected cells overexpressing
recombinant InsP3Rs. In contrast, nuclei from cells
transfected with the vector alone had InsP3-dependent channel activity in only 1.5% of patches. With K+ (140 mM)
as the permeant ion, recombinant SII(+) and SII(
) channels had slope
conductances of 370 pS and 390 pS, respectively. The recombinant
channels were 4-fold more selective for Ca2+ over
K+, and their open probabilities were biphasically
regulated by cytoplasmic [Ca2+]. This approach provides a
powerful new methodology to study the permeation and gating properties
of recombinant mammalian InsP3Rs in a native mammalian
membrane environment at the single-channel level.
Biophys J, July 2001, p. 117-124, Vol. 81, No. 1
© 2001 by the Biophysical Society 0006-3495/01/07/117/08 $2.00
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