PMID- 7563026
OWN - NLM
STAT- MEDLINE
DCOM- 19951020
LR  - 20190821
IS  - 0022-2631 (Print)
IS  - 0022-2631 (Linking)
VI  - 145
IP  - 3
DP  - 1995 Jun
TI  - Use of 82Br- radiotracer to study transmembrane halide flux: the effect of a 
      tranquilizing drug, chlordiazepoxide on channel opening of a GABAA receptor.
PG  - 257-66
AB  - We used the short-lived radionuclide, 82Br- to follow gamma-aminobutyrate (GABA) 
      receptor-mediated halide exchange into membrane vesicles from rat cerebral cortex 
      in millisecond and second time regions using quench-flow technique. The 
      radioisotope was prepared by neutron capture [81Br-(n,gamma)82Br-] on irradiation 
      of a natural isotope of bromine, 81Br- in a neutron flux. 82Br- decays by 
      beta-emission with secondary gamma-emission. Possible advantages of 82Br- over 
      36Cl- in anion tracer measurements include, (a) a short lifetime (t1/2 = 35.3 
      hr), which alleviates contamination and disposal problems, (b) high counting 
      efficiency (1.54) due to the secondary radiation, (c) measurement with a 
      gamma-counter as well as a beta-counter, (d) a simple preparation not requiring 
      subsequent purification steps giving a specific activity depending on the 
      irradiation time. With 6 hr irradiation time the specific activity was sufficient 
      to make measurements with < 1 mM Br-, which is less than the bromide 
      concentration known to affect the properties of GABAA receptor. The radiotracers, 
      82Br- and 36Cl- could be compared with the same solution composition. In 
      conditions where a direct effect of binding of halide to receptor does not 
      contribute to a difference in measured ion-flux, 82Br- was translocated only 
      marginally faster than 36Cl-. The effect of chlordiazepoxide (CDPX) (2-250 
      microM) on the progress of GABA (10 microM)-mediated 82Br- uptake was measured in 
      a time range of 200 msec to 20 sec using quench-flow technique. The two phases of 
      anion exchange previously reported in this experimental model with GABA alone 
      were observed. The rate of 82Br- exchange was increased 2.3-fold at 30-60 microM 
      CDPX and was not further increased with increasing [CDPX]. The rate of halide 
      exchange is a measure of open channel concentration. The isotope exchange rate 
      constant, J, in a membrane vesicle preparation, is a measure of the membrane 
      permeability per internal volume/surface area, J = PmA/V. Receptor 
      desensitization rate was also increased by CDPX, but unlike the isotope exchange 
      rate, it continued to increase up to at least 250 microM CDPX.
FAU - Cash, D J
AU  - Cash DJ
AD  - Department of Biochemistry, School of Medicine, University of Missouri, Columbia 
      65211, USA.
FAU - Serfozo, P
AU  - Serfozo P
FAU - Zinn, K
AU  - Zinn K
LA  - eng
PT  - Comparative Study
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - United States
TA  - J Membr Biol
JT  - The Journal of membrane biology
JID - 0211301
RN  - 0 (Bromides)
RN  - 0 (Bromine Radioisotopes)
RN  - 0 (Chlorides)
RN  - 0 (Receptors, GABA-A)
RN  - 56-12-2 (gamma-Aminobutyric Acid)
RN  - 6RZ6XEZ3CR (Chlordiazepoxide)
SB  - IM
MH  - Animals
MH  - Bromides/*metabolism/pharmacology
MH  - Bromine Radioisotopes
MH  - Cell Membrane/metabolism
MH  - Cell Membrane Permeability/drug effects
MH  - Chlordiazepoxide/*pharmacology
MH  - Chlorides/metabolism
MH  - In Vitro Techniques
MH  - Ion Transport
MH  - Kinetics
MH  - Male
MH  - Rats
MH  - Rats, Sprague-Dawley
MH  - Receptors, GABA-A/*drug effects/*metabolism
MH  - gamma-Aminobutyric Acid/metabolism
EDAT- 1995/06/01 00:00
MHDA- 1995/06/01 00:01
CRDT- 1995/06/01 00:00
PHST- 1995/06/01 00:00 [pubmed]
PHST- 1995/06/01 00:01 [medline]
PHST- 1995/06/01 00:00 [entrez]
AID - 10.1007/BF00232717 [doi]
PST - ppublish
SO  - J Membr Biol. 1995 Jun;145(3):257-66. doi: 10.1007/BF00232717.