Both dinitrophenol and Ba 2+ reduce KCl and fluid secretion in Malpighian tubules of Formica polyctena : The role of the apical H + and K + concentration gradient
Journal of Insect Physiology, ISSN: 0022-1910, Vol: 39, Issue: 12, Page: 1061-1073
1993
- 23Citations
- 10Captures
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Article Description
In the present study, further evidence is presented for the close relationship between fluid secretion and the ratio of the apical H + over K + concentration gradient. Two agents with a fast and reversible inhibitory effect on fluid secretion were tested on intracellular and luminal H + and K + concentrations and on transepithelial and transmembrane potential differences: 6 mM Ba 2+, a K + channel blocker, and 2·10 −4 M, 2,4-dinitrophenol (DNP), a well-known protonophore and uncoupler of oxidative phosphorylation. Ba 2+ hyperpolarized the apical membrane potential difference (V ap, lumen reference) from −59 ± 3 to −90 ± 6 mV ( n = 6) and the basal membrane potential difference (V bl ) from −23 ± 3 to −74 ± 7 mV ( n = 6). At the same time, the cell acidified (H c increased from 18 ± 4 to 50 ± 21 nM and the lumen alkalinized (H l decreased from 117 ± 23 to 74 ± 11 nM); H l /H c was reduced from 7.7 ± 2.4 to 2.8 ± 0.8 ( n = 6). On the other hand, K c dropped from 85 ± 6 to 73 ± 6 mM ( n = 9) and K l from 143 ± 3 to 121 ± 1 mM ( n = 5); consequently K l /K c remained unchanged (i.e. 1.7 ± 0.1). As a result, the H l /H c over K l /K c ratio decreased from 4.5 to 1.7. DNP depolarized V ap from −63 ± 7 to −26 ± 3 mV ( n = 8); V bl slightly depolarized from −21 ± 1 to 20 ± 1 mV. In the presence of 6 mM Ba 2+, V ap and the basal membrane potential difference (V bl ) (bath reference) depolarized from −81 ± 5 to 1 ± 2 mV and from −68 ± 6 to 1 ± 1 mV, respectively ( n = 5) when applying DNP. Like Ba 2+, the addition of 2·10 −4 M DNP to the control solution caused an acidification of the cytosol (H c rose from 24 ± 5 to 81 ± 9 nM); H l was not significantly changed (i.e. 80 ± 12 and 80 ± 9 nM in the absence and presence of DNP, respectively). Consequently, H l /H c dropped from 3.0 ± 0.7 to 1.0 ± 0.2 ( n = 8). K c diminished from 104 ± 9 to 80 ± 5 mM and K l from 141 ± 8 to 93 ± 6 mM after the addition of DNP; K l /K c was not significantly changed (i.e. 1.4 ± 0.1 and 1.2 ± 0.2 in the absence and presence of DNP, respectively, n = 6). The overall result was a reduction of the ratio (H l /H c over K l /K c ) from 2.1 to 0.8. On the other hand, the sensitivity of V bl and V ap to a change in bath K + from 5 to 51 mM was virtually unchanged from control in the presence of 2·10 −4 MDNP: V bl depolarized with 33 ± 1 and 32 ± 1 mV, and V ap with 19 ± 3 and 22 ± 1 mV, in the absence and presence of DNP, respectively. Furthermore, the transient changes of V bl on varying the bath K +, suggesting a change in K c, were comparable whether DNP was present or absent. These findings are consistent with the hypothesis of an apical K + /H + antiporter. Ba 2+ and DNP reduce the driving force for K + secretion to the lumen by slowing down the K + /H + antiporter. Ba 2+ increases the electrical component of the proton motive force of the electrogenic H + pump, thereby decreasing the free energy for building up a proton concentration gradient. DNP inhibits the realization of an apical lumen to cell directed H + concentration gradient by a double action mechanism. It depletes the apical H + pump from its energy source, and it can dissipate H + gradients via its protonophore action at the basal (and apical) cell membrane(s). Further evidence is presented for the electroneutrality of the K + /H + antiporter.
Bibliographic Details
http://www.sciencedirect.com/science/article/pii/002219109390130J; http://dx.doi.org/10.1016/0022-1910(93)90130-j; http://www.scopus.com/inward/record.url?partnerID=HzOxMe3b&scp=38249000626&origin=inward; http://linkinghub.elsevier.com/retrieve/pii/002219109390130J; http://api.elsevier.com/content/article/PII:002219109390130J?httpAccept=text/xml; http://api.elsevier.com/content/article/PII:002219109390130J?httpAccept=text/plain; https://linkinghub.elsevier.com/retrieve/pii/002219109390130J; https://api.elsevier.com/content/article/PII:002219109390130J?httpAccept=text/xml; https://api.elsevier.com/content/article/PII:002219109390130J?httpAccept=text/plain; http://dx.doi.org/10.1016/0022-1910%2893%2990130-j; https://dx.doi.org/10.1016/0022-1910%2893%2990130-j
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