High conductance Ca2+-activated K+ channels (BK channels) were previously demonstrated in the eel intestine. They are activated following a hypotonic stress and sustain Regulatory Volume Decrease. The aim of the present work was to address the possible role of BK channels in the Apoptotic Volume Decrease (AVD) and the possible interaction between BK channel activation and the progression of apoptosis. Apoptosis detection was performed by confocal microscopy and annexin V and propidium iodide labelling; cell volume changes were monitored by video imaging. The study was carried out on isolated eel enterocytes. Within a few hours after isolation the cells underwent anoikis, i.e apoptosis induced by detachment from the extracellular matrix. They showed an early AVD preceding the appearance of annexin V positivity. When the cells were resuspended in high K+ solution or treated with iberiotoxin, AVD was completely abolished. AVD occurred in correspondence with an increase in the [Ca2+]i, suggesting that the inducer of the K+ efflux through BK channels is an increase in the [Ca2+]i. The inhibition of K+ efflux through BK channels significantly inhibited the apoptosis progression. In fact, it was able to inhibit the onset of the phosphatidylserin translocation and the much later occurring cell membrane disruption.

Results demonstrated that BK channels, which are involved in RVD in enterocytes, play also a crucial role in the AVD process and in the progression of apoptosis.