Electro-pharmacological profiles of two brain mitoplast anion channels: Inferences from single channel recording.

We have characterized the conduction and blocking properties of two different chloride channels from brain mitochondrial inner membranes after incorporation into planar lipid bilayers. Our experiments revealed the existence of channels with a mean conductance of 158 ± 7 and 301 ± 8 pS in asymmetrical 200 mM cis/50 mM trans KCl solutions. We determined that the channels were ten times more permeable for Cl- than for K+, calculated from the reversal potential using the Goldman-Hodgkin-Katz equation. The channels were bell-shaped voltage dependent, with maximum open probability 0.9 at ± 20 mV. Two mitochondrial chloride channels were blocked after the addition of 10 µM DIDS. In addition, 158 pS chloride channel was blocked by 300 nM NPPB, acidic pH and 2.5 mM ATP, whereas the 301 pS chloride channel was blocked by 600 µM NPPB but not by acidic pH or ATP. Gating and conducting behaviors of these channels were unaffected by Ca2+. These results demonstrate that the 158 pS anion channel present in brain mitochondrial inner membrane, is probably identical to IMAC and 301 pS Cl channel displays different properties than those classically described for mitochondrial anion channels.

Endoplasmic reticulum membrane potassium channel dysfunction in high fat diet induced stress in rat hepatocytes.

In a previous study we reported the presence of a large conductance K(+) channel in the membrane of endoplasmic reticulum (ER) from rat hepatocytes. The channel open probability (Po) appeared voltage dependent and reached to a minimum 0.2 at +50 mV. Channel activity in this case was found to be totally inhibited at ATP concentration 2.5 mM, glibenclamide 100 µM and tolbutamide 400 µM. Existing evidence indicates an impairment of endoplasmic reticulum functions in ER stress condition. Because ER potassium channels have been involved in several ER functions including cytoprotection, apoptosis and calcium homeostasis, a study was carried out to consider whether the ER potassium channel function is altered in a high fat diet model of ER stress. Male Wistar rats were made ER stress for 2 weeks with a high fat diet. Ion channel incorporation of ER stress model into the bilayer lipid membrane allowed the characterization of K(+) channel. Our results indicate that the channel Po was significantly increased at voltages above +30 mV. Interestingly, addition of ATP 7.5 mM, glibenclamide 400 µM and tolbutamide 2400 µM totally inhibited the channel activities, 3-fold, 4-fold and 6-fold higher than that in the control groups, respectively. Our results thus demonstrate a modification in the ER K(+) channel gating properties and decreased sensitivity to drugs in membrane preparations coming from ER high fat model of ER stress, an effect potentially linked to a change in ER K(+) channel subunits in ER stress condition. Our results may provide new insights into the cellular mechanisms underlying ER dysfunctions in ER stress.