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

doi:10.1016/0022-1910(93)90004-B

Journal of Insect Physiology

Volume 39, Issue 11, November 1993, Pages 945-958

https://doi.org/10.1016/0022-1910(93)90004-B Get rights and content

Abstract

Cellular and luminal K⁺ concentrations were measured in different bath K⁺ concentrations using double-barrelled K⁺-selective electrodes. The electrochemical gradient for K⁺ across the basal and the apical cell membrane was estimated. The experiments were performed in two Cl⁻ concentrations. In control Ringer (41 mM K⁺ and 57 mM Cl⁻) cell K⁺ was 82 mM and luminal K⁺ was 119 mM. On lowering bath K⁺ to 4 mM or increasing it to 90 mM cell K⁺ and to a lesser extent luminal K⁺ followed: cell K⁺ changed to 29 and 90 mM and luminal K⁺ to 106 and 132 mM, respectively. In a 143 mM Cl⁻ Ringer solution cellular and luminal K⁺ concentration showed a similar change with the basal K⁺ concentration. The basal membrane potential difference was almost equal to the equilibrium potential for K⁺ in all bath K⁺ and Cl⁻ concentrations tested and the estimated electrochemical gradient for K⁺ across the basal membrane was very small (inward, zero, or even outward in low bath K⁺). It tended to become more inward as the bath K⁺ increased. The methods for estimating such a small gradient and the idea of passive K⁺ uptake through K⁺ channels across this barrier was critically evaluated. The large transepithelial electrochemical gradient against which K⁺ was transported was primarily situated in the apical membrane. This gradient decreased as the bath K⁺ was elevated (and fluid secretion accelerated): an increase in the bath K⁺ reduced both the electrical and concentration step to be overcome for K⁺ secretion across the apical membrane. A double role for the bath K⁺ in the regulation of K⁺ secretion is proposed.

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

Abstract

J. Insect Physiol.

J. Insect Physiol.

J. Insect Physiol.

Insect Biochem.

J. Insect Physiol.

J. Insect Physiol.

J. Insect Physiol.

J. Insect Physiol.

Ion-selective microelectrodes: theory and technique

Intracellular free potassium, sodium and chloride measured with ion-selective microelectrodes from salivary gland cells of the snail Planorbis corneus

J. exp. Biol.

Urine formation by the Malpighian tubules of Calliphora. I. Cations

J. exp. Biol.

Ion-selective electrode studies on the effects of 5-hydroxytryptamine on the intracellular level of potassium in an insect salivary gland

J. exp. Biol.

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

Am. J. Physiol.

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Jap. J. Physiol.

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J. exp. Biol.

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Pflügers Arch.

Distribution of ions in a fluid-transporting epithelium determined by electron-probe X-ray micro-analysis

Nature

Electron microprobe and ion-selective microelectrode studies of fluid secretion in the salivary glands of Calliphora

J. exp. Biol.

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J. cell Sci.

KCl transport across an insect epithelium: II. Electrochemical potentials and electrophysiology

J. membr. Biol.

Basal K channels in an insect epithelium. Channel density, conductance, and block by barium

J. gen. Physiol.

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