In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 75, No. 10 ( 1978-10), p. 5190-5194
Abstract:
The effects of ATP, Mg 2+ , and various agents on pH gradient, membrane potential, and catecholamine transport across membranes of intact bovine chromaffin vesicles were investigated. Methylamine and thiocyanate (SCN - ) distributions across the vesicle membrane were used to estimate the H + concentration gradient and membrane potential, respectively. The H + concentration ratio (intravesiculanmedium) equals 16 when the medium pH is 6.9 and is unaltered by ATP and Mg 2+ . In the absence of ATP and Mg 2+ , the steady-state intravesicular S 14 CN - concentration is lower than the medium concentration. ATP and Mg 2+ cause an increased influx and a decreased efflux of SCN - that results in SCN - being concentrated in the vesicles 6- to 8-fold over the medium. The findings are consistent with an ATP,Mg 2+ -induced potential of approximately 50 mV (intravesicular side positive). Carbonyl cyanide p -trifluoromethoxyphenylhydrazone (FCCP), a H + translocater, and N -ethylmaleimide (NEM), a sulfhydryl reagent, decrease the SCN - ratio and, thus, the membrane potential in the presence of ATP and Mg 2+ . They have no effect on the H + concentration gradient. The rate of catecholamine uptake into vesicles is increased 4- to 6-fold by ATP and Mg 2+ . The ATP,Mg 2+ -stimulated uptake is inhibited by FCCP and NEM over the same concentration ranges that reduce the SCN - distribution (membrane potential). FCCP increases and NEM decreases vesicular membrane ATPase activity. Thus, catecholamine uptake is correlated to an inside-positive membrane potential, and not to ATPase activity. If catecholamine uptake is coupled to membrane potential, then a charged species must be involved in the transport mechanism. Reserpine and rotenone inhibit catecholamine influx but have no effect on the H + electrochemical gradient; they probably act at a step before coupling to the membrane potential (or the H + electrochemical gradient). Atractyloside, an inhibitor of nucleotide transport, has no effects on catecholamine transport or the H + electrochemical gradient.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.75.10.5190
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
1978
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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