On the regulation of K+ uniport in intact mitochondria by adenine nucleotides and nucleotide analogs
Respiring mitochondria drive the electrophoretic uptake of K+ and other cations. In the presence of permeant acids this transport leads to mitochondrial swelling if it is not compensated by electroneutral K+/H+ exchange mediated by the K+/H+ antiporter. The mechanism of influx has yet to be establis...
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Veröffentlicht in: | The Journal of biological chemistry 1993-01, Vol.268 (2), p.997-1004 |
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Zusammenfassung: | Respiring mitochondria drive the electrophoretic uptake of K+ and other cations. In the presence of permeant acids this transport
leads to mitochondrial swelling if it is not compensated by electroneutral K+/H+ exchange mediated by the K+/H+ antiporter.
The mechanism of influx has yet to be established; however, evidence is accumulating that in addition to leak pathways a specific
K+ channel or uniporter may be involved. We examine some of the properties of K+ uniport which are consistent with the existence
of a specific ATP-regulated K+ channel. In contrast to the K+/H+ antiporter, K+ uniport shows little dependence on pH. K+
uniport is, however, very sensitive to inhibition by adenine nucleotides. The maximum percent inhibition is increased from
40 to 60% by treatment of mitochondria with N-ethylmaleimide (30 nmol/mg) which stimulates K+ uniport 3.6-fold. N-Ethylmaleimide,
however, has no effect on the IC50 values which are 0.5, 2.3, and 8 microM for ADP, ATP, and AMP, respectively. GDP has no
effect, while carboxyatractyloside is found to inhibit. The nucleotide analogs Cibacron blue 3GA and erythrosin B exhibit
three effects on K+ uniport. Low doses partially inhibit K uniport (I50 = 0.13 microM Cibacron Blue), while higher doses stimulate
(EC50 = 13 microM Cibacron Blue). Stimulation is especially apparent in N-ethylmaleimide-treated mitochondria. These analogs
also antagonize inhibition by ATP. Since the EC50 values for this antagonism for these two drugs are similar, while the IC50
values for inhibition of ATP transport differ by a factor of five, we suggest that inhibition of K+ uniport by ATP is not
mediated via the adenine nucleotide translocase. These data are consistent with the existence of an ATP-regulated K+ channel
in the inner mitochondrial membrane. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/S0021-9258(18)54032-1 |