Intracellular H+ inhibits a cloned rat kidney outer medulla K+ channel expressed in Xenopus oocytes

Abstract

The pH sensitivity of a cloned rat kidney K+ channel, ROMK1, was examined after expression in Xenopus oocytes. Membrane currents and intracellular pH (pHi) were concomitantly monitored by the two-microelectrode voltage-clamp technique and a pH-sensitive microelectrode. Oocytes injected with ROMK1 cRNA developed a hyperpolarized resting potential of -98.7 +/- 0.98 mV and a slightly inwardly rectifying Ba(2+)-sensitive K+ current. Lowering external pH from 7.4 to 6.7 using membrane-permeable acetate buffer reduced measured pHi from 7.2 to 6.6 and reduced the ROMK1 current by 80%. The H+ blockade of ROMK1 currents was voltage independent. The relationship between ROMK1 slope conductance and pHi fitted to a titration curve suggested binding of four H+ to a site with a pK of 6.79. Extracellular acidification from pH 7.4 to 6.0 using membrane-impermeable biphthalate buffer had no effect on the ROMK1 current. The pH sensitivity of the ROMK1 channel is similar to that reported for a small-conductance native kidney K+ channel.

Rat Adrenal Chromaffin Cells Are Neonatal CO2Sensors

“…In addition, several cloned inward-rectifier or two-pore K ϩ channel classes also respond to CO 2 and intracellular pH similarly to the K ϩ currents seen in CO 2 -sensitive brainstem neurons (Putnam et al, 2004). Kir 1.1 and Kir 1.2 are inhibited by lowering intracellular pH (Tsai et al, 1995;Fakler et al, 1996) and hypercapnic acidosis Zhu et al, 2000). In contrast, regulation of nonselective cationic channels by intracellular pH is less studied.…”

A Shaker-like K+ Channel with Weak Rectification Is Expressed in Both Source and Sink Phloem Tissues of Arabidopsis

“…Adding acetate to the external solution is known to induce acidification of the cytosol (Roos and Boron, 1981;Tsai et al, 1995). The protonated form of this molecule can diffuse through the membrane into the cytosol, where it dissociates and releases protons.…”

“…Decreasing the external pH from 7.0 to 5.6 induced a decrease in the AKT2 current ( Figure 5A). Inhibition of the instantaneous current was twice that of the time-dependent current ( Figure 5C), suggesting that the mechanisms involved in AKT2 current inhibition by external acidification differ for the instantaneous and the time-dependent components of the current.Adding acetate to the external solution is known to induce acidification of the cytosol (Roos and Boron, 1981;Tsai et al, 1995). The protonated form of this molecule can diffuse through the membrane into the cytosol, where it dissociates and releases protons.…”

Molecular mechanism of a COOH-terminal gating determinant in the ROMK channel revealed by a Bartter's disease mutation

“…Because Kir1.1 is insensitive to extracellular pH (Tsai et al 1995), pH i -dependent changes in channel activity can be accurately determined in intact oocytes by changing extracellular pH in the presence of a permeant weak acid like butyrate (Leipziger et al 2001). Intracellular pH measurements were performed to construct a titration curve.…”

“…Like the native channel (Wang et al 1990), Kir1.1 channels are gated by intracellular pH, closing with cytoplasmic acidification (Tsai et al 1995, Choe et al 1997McNicholas et al 1998). Recent studies have begun to illuminate the pH-sensing mechanism, whereby two arginine residues in the cytoplasmic NH 2 -and COOH-termini, R41 and R311, (Fakler et al 1996;Schulte et al 1999) functionally interact with the pH sensor, K80, in the cytoplasmic NH 2 -terminus (Fakler et al 1996;Schulte et al 1999) to adjust the titration of the residue into a physiological range of pH sensitivity.…”