Elsevier

Journal of Insect Physiology

Volume 39, Issue 12, December 1993, Pages 1061-1073
Journal of Insect Physiology

Both dinitrophenol and Ba2+ reduce KCl and fluid secretion in Malpighian tubules of Formica polyctena: The role of the apical H+ and K+ concentration gradient

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Abstract

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 Ba2+, a K+ channel blocker, and 2·10−4 M, 2,4-dinitrophenol (DNP), a well-known protonophore and uncoupler of oxidative phosphorylation. Ba2+ hyperpolarized the apical membrane potential difference (Vap, lumen reference) from −59 ± 3 to −90 ± 6 mV (n = 6) and the basal membrane potential difference (Vbl) from −23 ± 3 to −74 ± 7 mV (n = 6). At the same time, the cell acidified (Hc increased from 18 ± 4 to 50 ± 21 nM and the lumen alkalinized (Hl decreased from 117 ± 23 to 74 ± 11 nM); Hl/Hc was reduced from 7.7 ± 2.4 to 2.8 ± 0.8 (n = 6). On the other hand, Kc dropped from 85 ± 6 to 73 ± 6 mM (n = 9) and Kl from 143 ± 3 to 121 ± 1 mM (n = 5); consequently Kl/Kc remained unchanged (i.e. 1.7 ± 0.1). As a result, the Hl/Hc over Kl/Kc ratio decreased from 4.5 to 1.7. DNP depolarized Vap from −63 ± 7 to −26 ± 3 mV (n = 8); Vbl slightly depolarized from −21 ± 1 to 20 ± 1 mV. In the presence of 6 mM Ba2+, Vap and the basal membrane potential difference (Vbl) (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 Ba2+, the addition of 2·10−4 M DNP to the control solution caused an acidification of the cytosol (Hc rose from 24 ± 5 to 81 ± 9 nM); Hl was not significantly changed (i.e. 80 ± 12 and 80 ± 9 nM in the absence and presence of DNP, respectively). Consequently, Hl/Hc dropped from 3.0 ± 0.7 to 1.0 ± 0.2 (n = 8). Kc diminished from 104 ± 9 to 80 ± 5 mM and Kl from 141 ± 8 to 93 ± 6 mM after the addition of DNP; Kl/Kc 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 (Hl/Hc over Kl/Kc) from 2.1 to 0.8. On the other hand, the sensitivity of Vbl and Vap to a change in bath K+ from 5 to 51 mM was virtually unchanged from control in the presence of 2·10−4 MDNP: Vbl depolarized with 33 ± 1 and 32 ± 1 mV, and Vap with 19 ± 3 and 22 ± 1 mV, in the absence and presence of DNP, respectively. Furthermore, the transient changes of Vbl on varying the bath K+, suggesting a change in Kc, were comparable whether DNP was present or absent. These findings are consistent with the hypothesis of an apical K+/H+ antiporter. Ba2+ and DNP reduce the driving force for K+ secretion to the lumen by slowing down the K+/H+ antiporter. Ba2+ 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.

References (41)

  • A. Leyssens et al.

    Intrinsic regulation of K+ transport in Malpighian tubules (Formica): electrophysiological evidence

    J. Insect. Physiol.

    (1992)
  • A. Leyssens et al.

    Measurement of intracellular and luminal K+ concentrations in a Malpighian tubule (Formica). Estimate of basal and luminal K+ electrochemical gradients

    J. Insect. Physiol.

    (1993)
  • P.J. Morgan et al.

    Stimulated fluid secretion is sodium dependent in the Malpighian tubules of Locusta migratoria

    J. Insect Physiol.

    (1981)
  • E. Van Kerkhove et al.

    Haemolymph composition in Formica (Hymenoptera) and urine formation by the short isolated Malpighian tubules: electrochemical gradients for ion transport

    J. Insect Physiol.

    (1989)
  • P.S. Aronson

    Identifying secondary active solute transport in epithelia

    Am. J. Physiol.

    (1981)
  • A.C. Chao et al.

    Basal membrane uptake in potassium-secreting cells of midgut of tobacco hornworm (Manduca sexta)

    Am. J. Physiol.

    (1990)
  • A.C. Chao et al.

    Cytoplasmic pH and goblet cavity pH in the posterior midgut of the tobacco hornworm Manduca sexta

    J. exp. Biol.

    (1991)
  • S. Dijkstra et al.

    Two effects of DNP on Malpighian tubules of the ant

    Archs int. Physiol. Biochim.

    (1993)
  • J.D. Gifford et al.

    H+K+-ATPase activity in rat collecting duct segments

    Am. J. Physiol.

    (1992)
  • J.W. Hanrahan et al.

    Basolateral K channels in an insect epithelium: channel density, conductance and block by barium

    J. gen. Physiol.

    (1986)
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