Evidences on the existence of a new potassium channel in the rough endoplasmic reticulum (RER) of rat hepatocytes

Introduction: we have recently reported the presence of two potassium currents with 598 and 368 pS conductance in the rough endoplasmic reticulum (RER) membrane. The 598 pS channel was voltage dependent and ATP sensitive. However, the 368 pS channel was rarely observed and its identity remained obscure. Since cationic channels in intracellular organelles such as mitochondria and RER play important roles in intracellular signaling and cellular protection, studying their biophysical and pharmacological properties is important. Methods: we used channel incorporation into bilayer lipid membrane method. L-α-Phosphatidylcholine (PC), a membrane lipid, was extracted from fresh egg yolk. Bilayer lipid membrane was formed in a 150 μm diameter hole. Rough endoplasmic reticulum vesicles were obtained from liver after homogenization and several centrifugations. All recordings were filtered at 1 kHz and stored at a sampling rate of 10 kHz for offline analysis by PClamp9. Statistical analysis was performed based on Markov noise free single channel analysis. Results: A 364 pS potassium channel was identified which was voltage independent in +50 to -50 mV voltages. In all voltages, open probability (Po) was over 0.9. Nonspecific inhibitor of K+ channels, 4-aminopyridine (4-AP, 20 mM), inhibited the channel activity. However, intracellular nucleotide like ATP had no effect on channel gating. Conclusion: We observed a new potassium channel with 346 pS conductance in RER membrane that unlike the 598 pS K channel was not ATP sensitive. This channel may play an important role in Ca2+ homeostasis and cell protection.