now been observed that intracellular calcium levels 
also affect the sensitivity of the channels to agonist. 
The effects of muscarine and LH-RH (luteinizing 
hormone-releasing hormone) are much smaller 
when intracellular calcium is completely absent, 
suggesting that calcium-dependent proteins partici- 
pate in the transduction pathway. 
Arachidonic acid increases M current, and phos- 
pholipase A2 inhibitors, such as quinacrine and bro- 
mophenacyl bromide, prevent both overrecovery 
and calcium-induced enhancement of M current. 
Furthermore, 1 2-lipoxygenase pathway metabolites 
mimic calcium enhancement and overrecovery, 
while the 1 2-lipoxygenase pathway inhibitor baica- 
lein inhibits all these effects. Thus arachidonic acid 
metabolites are plausible mediators of both calcium 
enhancement and overrecovery. However, these 
pathways do not appear to be involved in the pri- 
mary inhibition elicited by agonists. 
Dr. Adams is also Professor of Neurobiology 
and Behavior and of Pharmacological Sciences at 
the State University of New York at Stony Brook. 
Articles 
Lopez, H.S. 1992. Kinetics of G protein-mediated 
modulation of the potassium M-current in bull- 
frog sympathetic neurons. Neuron 8:725-736. 
Marrion, N.V., and Adams, P.R. 1992. Release of 
intracellular calcium and modulation of mem- 
brane currents by caffeine in bull-frog sympa- 
thetic neurones. /P^js/o/ (Lond) 445:515-535. 
Marrion, N.V., Adams, P.R., and Gruner, W. 
1992. Multiple kinetic states underlying macro- 
scopic M-currents in bullfrog sympathetic neu- 
rons. Proc R Soc Lond (Biol) 248:207-214. 
MOLECULAR MECHANISMS OF VOLTAGE-GATED ION CHANNEL FUNCTION 
Richard W. Aldrich, Ph.D., Associate Investigator 
Voltage-gated ion channels are the molecular ele- 
ments that underlie electrical signaling in excitable 
and nonexcitable cells. Among the important physi- 
ological processes in which they are involved are 
information processing and transmission in the ner- 
vous system, neuronal plasticity, initiation and regu- 
lation of the heartbeat, and muscle excitation. The 
voltage sensitivity and time course of opening and 
closing of these channels in response to changes in 
membrane potential determine how a given cell gen- 
erates electrical activity and responds to signals 
from other cells. The long-term goal of research in 
Dr. Aldrich's laboratory is to understand the molecu- 
lar mechanisms of ion channel function. 
Dr. Aldrich and his colleagues have studied gating 
processes in voltage-gated potassium channels from 
the Shaker family. Shaker channels have been used 
as a model system for voltage-dependent channel 
gating for several reasons. The subunits are smaller 
and therefore more readily manipulable than 
voltage-dependent sodium or calcium channels. 
The wide diversity of structural and physiological 
properties of channels in the Shaker superfamily 
can facilitate the identification of structural regions 
of particular functional significance. 
The general strategy has been to combine single- 
channel, macroscopic, and gating current measure- 
ments with alterations of channel structure by in 
vitro mutagenesis to define amino acid residues that 
are involved in specific conformational changes and 
to determine the biophysical mechanisms involved 
in these changes. The research has focused on three 
different gating processes: 1) inactivation mediated 
by the amino-terminal (N-rype inactivation), 2) a 
separate inactivation process mediated in part by res- 
idues in the sixth membrane-spanning region (C- 
rype inactivation), and 3) voltage-dependent chan- 
nel activation. 
Mechanisms of N-Type Inactivation 
Shaker channels become inactive quite rapidly 
after opening, within less than a millisecond in 
some Shaker variants. Previous studies by Drs. 
Aldrich, Toshinori Hoshi, and William Zagotta pro- 
vided evidence for a mechanism whereby an intra- 
cellular portion of the channel, consisting of amino 
acid residues near the amino terminal, effects inacti- 
vation, occluding the internal mouth of the channel. 
A crucial piece of evidence for this mechanism was 
that a synthetic peptide with the sequence of the 
amino-terminal domain was able to restore inactiva- 
tion in channels that did not inactivate because of 
mutations in the amino-terminal region. 
Dr. Ruth Murrell-Lagnado and Dr. Aldrich have 
investigated the determinants of the interaction be- 
tween the inactivation-inducing peptides and the 
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