Viral-mediated gene therapy for ion channel disorders in CNS and
skeletal muscle; Molecular mechanisms of ion channel function in
Aquaporins.
We are interested in understanding the ion channels that generate
signals and control cellular responses in excitable membranes
of brain, heart and skeletal muscle. Our research programs focus
on modifying the expression of potassium channels to control disease
states that are associated with aberrant activity in neurons and
skeletal muscle, and on discovering novel properties of a class
of channels called Aquaporins.
Overexpressing K+ channels to control hyperexcitability:
Simultaneous viral-mediated introduction of genes for voltage-gated
potassium channels dramatically changes cell excitability, and
serves as a potential strategy for ion channelopathies associated
with hyperexcitability. In collaboration with Dr. Scott Sherman
(Neurology), we use viral-driven K+ channel overexpression and
knockdown as a mechanism for compensating for aberrant patterns
of activity in muscle and brain. For example, introducing K+ channels
to slow firing rate in neurons of the hippocampus has potential
relevance as a treatment for epilepsy. The skeletal muscle disease,
Hyperkalemic Periodic Paralysis (HyperPP) is caused by defective
Na+ channels that fail to inactivate correctly and thus generate
sustained depolarizations that cause muscle weakness. We are testing
whether we can counterbalance hyperactivity by overexpressing
voltage-gated K+ channels, thereby augmenting the capacity of
excitable cells to recover after a stimulus. This work provides
important insight into the critical balance between Na+ and K+
conductances that drive electrical responses, and has potential
therapeutic value pending the likely development of improved viral
vector gene delivery systems that are safe for use in humans.
Analyzing the molecular basis of ion channel function in aquaporins:
Aquaporin-1 (Aqp1) is expressed in kidney, blood vessels, red
blood cells, the interior of the brain and the eye, and is known
to form conduits for water flow across cell membranes. Our work
in collaboration with W. Daniel Stamer at the University of Arizona
has shown that Aqp1 channels are not simply "holes"
in the cell membrane, but also are subject to regulation by intracellular
signaling pathways. Novel attributes of Aqp1 include an ion channel
conductance that is controlled through intracellular cyclic GMP.
Our work characterizes the functional properties of Aqp1 proteins,
and uses molecular techniques to determine the regions of the
Aqp1 channel that enable the regulated responses. Other Aquaporins
may also be found to function as ion channels, if activated by
an appropriate stimulus.
Muller, Y.L., Reitstetter, R. and A.J. Yool. 2000. Antisense
knockdown of calcium-dependent K+ channels in developing cerebellum.
Dev. Brain Research 120: 135-140.
Anthony, T.L., H.L. Brooks, D. Boassa, S. Leonov, G. Yanochko,
J.W. Regan and A.J. Yool, 2000. Characterization of cloned human
Aquaporin-1 as a cyclic-GMP-gated ion channel. Mol. Pharmacol.
57: 576-588.
Brooks, H.L., J.W. Regan and A.J. Yool. 2000. Inhibition of Aquaporin-1
water permeability by TEA: Involvement of the loop E pore region.
Molecular Pharmacology 57: 1021-1026.
Falk, T., L.A. Strazdas, R.S. Borders, R.K. Kilani, A.J. Yool
and S.J. Sherman. 2001. A herpes simplex viral vector expressing
green fluorescent protein can be used to visualize morphological
changes in high-density neuronal culture. Electronic J. Biotechnol.,
April 15; www.ejb.org/content/vol4/issue1/full/5/index.html
Falk T, R.K. Kilani, A.J. Yool and S.J. Sherman. 2001. Viral-vector
mediated expression of K+ channels regulates electrical excitability
in skeletal muscle cells. Gene Therapy 8: 1372-1379.
Steidl JV and AJ Yool. 2001. Distinct mechanisms of block of
Kv1.5 channels by tertiary and quaternary amine clofilium compounds.
Biophysical J. 81: 2606-2613.
Anthony, T.L., Fujino, H., Pierce, K.L., Yool, A.J., Regan, J.W.
2002. Differential regulation of Ca2+-dependent Cl- currents by
FP prostanoid receptor isoforms in Xenopus oocytes. Biochem. Pharmacol.
63: 1797-1806.
Yool AJ, Brokl OH, Pannabecker TL, Dantzler WH and Stamer WD.
2002.Tetraethylammonium block of water flux in Aquaporin-1 channels
expressed in kidney thin limbs of Henle's loop and a kidney-derived
cell line. BMC Physiology 2: 4.
Yool AJ and Weinstein AM. 2002. New roles for old holes: Ion channel
function in Aquaporin 1. News In Physiol. Sci., 17: 68-72.
Yanochko GM and Yool AJ. 2002. Regulated cationic channel function
in Xenopus oocytes expressing Drosophila Big Brain. J. Neuroscience
22: 2530-2540.
Yool, A.J. and W.D. Stamer. 2002. Novel roles for Aquaporins
as gated ion channels. In: Principles of Medical Biology "Molecular
Insights into Ion Channel Biology in Health and Disease."
In press.
Boassa D and AJ Yool. 2002. A fascinating tail: cGMP activation
of aquaporin-1 ion channels. Trends Pharmacol Sci, (Dec). In press.
