Volume-sensitive Cl− Current in Bovine Adrenocortical Cells: Comparison with the ACTH-induced Cl− Current

Abstract

In a previous study performed on zona fasciculata (ZF) cells isolated from calf adrenal glands, we identified an ACTH-induced Cl- current involved in cell membrane depolarization. In the present work, we describe a volume-sensitive Cl- current and compare it with the ACTH-activated Cl- current. Experiments were performed using the whole-cell patch-clamp recording method, video microscopy and cortisol-secretion measurements. In current-clamp experiments, hypotonic solutions induced a membrane depolarization to -22 mV. This depolarization, correlated with an increase in the membrane conductance, was sensitive to different Cl- channel inhibitors. In voltage-clamp experiments, hypotonic solution induced a membrane current that slowly decayed and reversed at -21 mV. This ionic current displayed no time dependence and showed a slight outward rectification. It was blocked to variable extent by different conventional Cl- channel inhibitors. Under hypotonic conditions, membrane depolarizations were preceded by an increase in cell volume that was not detected under ACTH stimulation. It was concluded that hypotonic solution induced cell swelling, which activated a Cl- current involved in membrane depolarization. Although cell volume change was not observed in the presence of ACTH, biophysical properties and pharmacological profile of the volume-sensitive Cl- current present obvious similarities with the ACTH-activated Cl- current. As compared to ACTH, hypotonic solutions failed to trigger cortisol production that was weakly stimulated in the presence of high-K+ solution. This shows that in ZF cells, membrane depolarization is not a sufficient condition to fully activate secretory activities.

Differential dependence of regulatory volume decrease behavior in rabbit corneal epithelial cells on MAPK superfamily activation

“…Another contributor to RVD in human CEC (HCEC) and some other tissues is the K-Cl cotransporter (KCC) (Capo-Aponte et al, 2005, 2007aErnest et al, 2005). Even though volume sensitive Cl − channel activity was identified in many tissues, nothing is known about the role of K + as a counterion to Cl − egress in RCEC (AlNakkash et al, 2004;Dupre-Aucouturier et al, 2004;Hazama and Okada, 1988;Inoue et al, 2005) The ability of cells to regulate their cellular volume during exposure to an anisosmotic challenge is essential for sustaining their proliferative (Lang et al, 2005;Schreiber, 2005), migratory (Mao et al, 2005;Soroceanu et al, 1999) and secretory activity (Do et al, 2006;Strbak and Greer, 2000). Such responses are dependent on receptor mediated differential mitogen protein kinase (MAPK) activation.…”