Ion channels in the inner mitochondrial membrane as tools for studying apoptosis and neuroprotection

Abstract

Since several years ion channels of the inner mitochondrial membrane are known to be of significance for apoptosis or neuroprotection. It was shown that the blockade of the largest of them, the permeability transition pore (PTP) can suppress apoptotic cell death (Andrabi et al., FASEB J, in press) and that keeping potassium channels open, like the K(Ca)- or the K(ATP)-channel, protects cells from ischemic preconditioning. We prepared mitoplasts i.e. vesicles of inner mitochondrial membrane by a hypotonic treatment of the mitochondria and studied four different ion channels by means of the patch-clamp method. We show here that the K(Ca)-channel is the dominant channel in astrocyte and in glioma mitochondria. Voltage dependence, Ca-sensitivity and pharmacological behaviour resemble that of their counterpart in the plasma membrane. Similar to this channel, the mtK(ATP)-channel was shown to protect cells from ischemic injury. This channel was described as a single channel only once in 13 years until we have rediscovered it now (Dahlem et al., BBA-Bioenergetics, in press). We show the biophysical and some pharmacological properties, in particular block by NO. Furthermore, we studied the single-channel behaviour of the PTP and found that the channel could be directly blocked by two substances that have clearly neuroprotective properties, the dopamin-D2-agonist Pramipexole (Sifrol) with an IC50 of 500 nM and melatonin (IC50=800nM). We could show at least for melatonin that this effect is due to a reduced rate of neuronal cell death. Finally, a 108 pS Cl-channel that was shown to be identical with inner membrane anion channel (IMAC) can be blocked by fatty acids.