ISSN:
1573-6830
Keywords:
catecholamine
;
chromaffin granules
;
reserpine
;
N-ethylmaleimide
;
transporter
;
Mg ATPase
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary 1. Catecholamines are transported into chromaffin granules via a carriermediated, active-transport process which is inhibited by micromolar concentrations of the sulfhydryl reagent,N-ethylmaleimide (NEM). Reserpine is a very potent, competitive inhibitor of the catecholamine transporter and can be used to investigate the characteristics of the catecholamine transporter. 2. The purpose of this study was to determine whether [3H]reserpine binding to the catecholamine transporter present in chromaffin granule membranes isolated from bovine adrenal glands was also inhibited by NEM and, if so, whether this was a direct or an indirect effect of NEM on the catecholamine transporter. 3. Both [3H]norepinephrine transport into and [3H]reserpine binding to the chromaffin granule ghosts isolated from bovine adrenal glands are inhibited by NEM, with IC50 values of 0.63 ± 0.02 and 2.8 ± 0.66µM, respectively. 4. Mg and ATP protected both the [3H]norepinephrine transport into the ghosts and the [3H]reserpine binding to the transporter from inhibition by NEM, shifting the IC50 values to 260 ± 43 and 120 ± 29µM, respectively. 5. NEM inhibition of the catecholamine transport and reserpine binding appears to be due to an action on the proton translocator associated with the Mg ATPase enzyme rather than a direct action on the catecholamine transporter since (a) the concentration of NEM required to inhibit formation of a membrane potential is similar to that required to inhibit [3H]norepinephrine transport into and [3H]reserpine binding to the ghosts and (b) Mg and ATP protected the proton translocation and [3H]norepinephrine transport into the ghosts, and [3H]reserpine binding to the ghosts, from inhibition by NEM. 6. The results support the concept that reserpine is binding to the catecholamine site on the granule membranes and that binding of reserpine requires the presence of a membrane potential.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00711247
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