Volume regulation in a toad epithelial cell line: role of coactivation of K+ and Cl‐ channels.

Abstract

1. We have measured changes in cell volume, membrane potential and ionic currents in distal nephron A6 cells following a challenge with hypotonic solutions (HTS). 2. The volume increase induced by HTS is compensated by a regulatory volume decrease (RVD), which is inhibited by both 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) and quinine. Quinine (500 uM) completely blocked RVD, whereas 100 /M NPPB delayed and attenuated RVD.3. The resting potential in A6 cells was -52-3 + 4.8 mV (n = 53), and shifted to -35-1 + 2-2 mV (n = 33) during HTS. 4. Resting membrane current in A6 cells was 0 35 + 0-12 pA pF-1 at -80 mV and 0-51 + 0-16 pA pF-1 at +80 mV (n = 5). During cell swelling these values increased to 11.5 + 1 1 and 29-3 + 2-8 pA pF-1 (n = 29), respectively. 5. Quinine (500 /zM) completely blocked the HTS-activated current at -15 mV, the reversal potential for Cl-currents, but exerted only a small block at -100 mV (K+ equilibrium potential). NPPB (100 /M) inhibited the current at both potentials almost to the same extent. The HTS-induced net current reversed at -41 + 2-5 mV (n = 15), which is close to the measured resting potential during HTS. 6. The quinine-insensitive current reversed near the Cl-equilibrium potential. The quininesensitive current reversed near the K+ equilibrium potential. The respective conductances activated by HTS at the zero-current potential were 2-1 + 0 7 nS for K+ and 5-2 + 1-3 nS for Cl (n = 15). 7. Single channel analysis unveiled activation of at least two different channels during HTS.A 36 pS channel reversing at the Cl-equilibrium potential showed increased open probability at depolarized potentials. HTS also activated a K+ channel with a 29 pS conductance in high-K+ extracellular solutions (130 mM) or 12 pS in 2-5 mm K+.8. This coactivation of K+ and Cl-channels shifts the membrane potential towards a value between EK and Eci (the reversal potentials for K+ and CF), where a net efflux of Cl-(Clinward current) and K+ (K+ outward current) under zero-current conditions occurs. Block of either the K+ or the Cl-conductance will shift the zero-current potential towards the equilibrium potential of the unblocked channel, preventing net efflux of osmolytes and RVD. This coactivation of K+ and Cl-currents causes a shift of osmolytes out of the cells, which almost completely accounts for the observed RVD.Processes involved in the regulation of cell volume have We have recently shown that a challenge with hyposmotic been widely studied during the last 10 years (for reviews, solutions was not followed by a regulatory volume decrease see McCarty

Ions, cell volume, and apoptosis

“…K ϩ efflux can be expected to induce an accompanying Cl Ϫ efflux to maintain electroneutrality, and vice versa; water can be expected to follow KCl efflux. Thus either K ϩ or Cl Ϫ channel blockers will likely attenuate the efflux of both ions (46). As outlined above, reduction in [K ϩ ] i below normal physiological levels has been specifically proposed to facilitate the activation of caspases and endonucleases involved in apoptosis, so an extreme, albeit parsimonious, perspective, alternative to that proposed by Maeno et al, (Fig.…”

Swelling-activated taurine and K + transport in human cervical cancer cells: association with cell cycle progression

“…In contrast, the activation of volume-sensitive KCC, at least, is independent of extracellular Ca 2+ . Volume-sensitive K + channels have been described in Ehrlich ascites tumour cells [7], tracheal epithelial cells [3], distal nephron A6 cells [21], bovine aortic endothelial cells [26], human T lymphocytes [12] and murine erythroleukaemia cells [35]. The relationship between Ca 2+ and volumesensitive K + channels is, however, controversial.…”

Influence of Calcium on Regulatory Volume Decrease: Role of Potassium Channels

“…RVD in all these cells is Ca 2+ independent. Somehow divergent from these two groups are the epithelial cell lines MDCK and A6 which exhibit a Ca 2+ -dependent RVD and small, Ca 2+ -dependent osmosensitive K + channels [84, 85, 86]. …”