Received August 23, 2005
Revised September 23, 2005
Accepted after revision October 11, 2005
Drosophila 'tweety' family may encode a large-
conductance Ca2+ activated Cl- channels
Suzuki Makoto 1*
1 Jichi Medical School
* To whom correspondence should be addressed. E-mail: macsuz{at}jichi.ac.jp.
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Abstract |
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Calcium-activated chloride (CaC) currents can be
recorded in almost all cells, but there is still little
information on the molecular nature of the channel
underlying this conductance. I report here that tweety,
a gene located in Drosophila flightless, possesses five
or six transmembrane segments and that a human homologue
of tweety (hTTYH3) is a novel large-conductance CaC
channel and hTTYH1 involves a swell-activated current.
hTTYH3 mRNA was found to be distributed in excitable
tissues: heart, brain and skeletal muscle. The whole
cell current of hTTYH3 did not differ until a rise in
intracellular Ca2+ induced by ionomycin. The hTTYH3-
induced linear current was large enough to be
discriminated from the control. Analysis of pore-mutants
suggested that positively charged amino acids
contributed to anion selectivity. The current was not
altered by dithiothreitol or niflumate but blocked by
DIDS. Single channel conductance was 260 pS and
permeability order was I>Br>Cl. Like a CaC channel in
situ, opening of the hTTYH3 channel showed complex
kinetic, voltage-dependent inactivation and is dependent
on micro-molar internal Ca2+. Likewise investigation of
hTTYH1 was performed. A spliced variant form of hTTYH1
(hTTYH1sv) lacking C-terminal E-rich domain was
expressed in CHO cells. In contrast to hTTYH3, hTTYH1sv
showed a swell-activated current. The current was not
inhibited by NPPB but by DIDS. hTTYH1sv encodes 200 pS
outwardly rectified large-conductance channel.
Therefore, investigation of the tweety family will
provide important information of large-conductance Cl-
channel molecules.
Key Words:
Chloride channel, Electrophysiology, Molecular biology
