Role of BK channels in the apoptotic volume decrease in native Eel intestinal cells

High conductance Ca ⁺ -activated K ⁺ channels (BK channels) have previously been demonstrated in the eel intestine. They are specifically activated following a hypotonic stress and sustain Regulatory Volume Decrease (RVD). The aim of the present work was to address the possible role of these channels in the Apoptotic Volume Decrease (AVD) of isolated eel enterocytes, and the possible interaction between BK channels and the progression of apoptosis. The detection of apoptosis was performed by confocal microscopy and annexin V and propidium iodide labelling; cell volume changes were monitored by video imaging. Within a few hours after isolation, enterocytes underwent anoikis (apoptosis induced by detachment from the extracellular matrix). They showed an early normotonic volume decrease (AVD) preceding the appearance of annexin V positivity. AVD occurred in correspondence with an increase in the [Ca ²⁺ ] _i , measured with Fura-2. When the cells were resuspended in high K ⁺ solution or treated with iberiotoxin, AVD was completely abolished. In addition, treatment with high K ⁺ or iberiotoxin significantly inhibited apoptosis progression. It was demonstrated for the first time in native enterocytes that BK channels, which are involved in RVD in these cells, plays also a crucial role in the AVD process and in the progression of apoptosis.