Mechanisms of two modulatory actions of the channel-binding protein Slob on the Drosophila Slowpoke calcium-dependent potassium channel

Oxidative Stress and Maxi Calcium-Activated Potassium (BK) Channels

All cells contain ion channels in their outer (plasma) and inner (organelle) membranes. Ion channels, similar to other proteins, are targets of oxidative impact, which modulates ion fluxes across membranes. Subsequently, these ion currents affect electrical excitability, such as action potential discharge (in neurons, muscle, and receptor cells), alteration of the membrane resting potential, synaptic transmission, hormone secretion, muscle contraction or coordination of the cell cycle. In this chapter we summarize effects of oxidative stress and redox mechanisms on some ion channels, in particular on maxi calcium-activated potassium (BK) channels which play an outstanding role in a plethora of physiological and pathophysiological functions in almost all cells and tissues. We first elaborate on some general features of ion channel structure and function and then summarize effects of oxidative alterations of ion channels and their functional consequences.

The inhibitory effect of angiotensin II on BKCa channels in podocytes via oxidative stress

Angiotensin II (Ang II) is an important active substance of the renin-angiotensin system (RAS). The present study has confirmed that abnormalities of Ang II may be related with cerebrovascular diseases, endocrine diseases, cardiovascular diseases, liver diseases, such as: cerebral hypoxia, diabetes, obesity, atrial fibrillation, and liver cirrhosis. However, understanding effects of Ang II on podocytes is not enough. This study was to investigate the effects of oxidative stress on the large conductance, Ca(2+)-activated K(+) channels (BKCa). Results from the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay showed that Ang II induced podocyte death in a concentration-dependent manner. The measurement of superoxide dismutase (SOD) generation demonstrated that Ang II decreased the total SOD of cellular levels. Meaningfully, pretreatment of a type of ROS scavenger formulations named N-(mercaptopropionyl)-glycine (N-MPG) could inhibit podocyte apoptosis induced by Ang II. Meanwhile, patch-clamp technique was used in this study to detect the effects of Ang II on currents of BKCa channel in podocytes. The results indicated that Ang II inhibited the current amplitude of BKCa channel and decreased the slope of I-V curve. Ang II also made the activation curves of BKCa channel shift to the left. These results may provide a theoretical basis for potential treatment of chronic glomerular disease in the future.

In vivo role of a potassium channel-binding protein in regulating neuronal excitability and behavior

Molecular details of ion channel interactions with modulatory subunits have been investigated widely in transfected cells, but the physiological roles of ion channel modulatory protein complexes in native neurons remain largely unexplored. The Drosophila large-conductance calcium-activated potassium channel (dSlo) binds to and is modulated by its binding partner Slob. We have constructed flies in which Slob expression is manipulated by P-element mutagenesis, or by transgenic expression of Slob protein or Slob-RNAi. In vivo recordings of both macroscopic and single dSlo channel currents in identified neurosecretory neurons in the pars intercerebralis (PI) region of the Drosophila brain reveal that whole-cell potassium current and properties of single dSlo channels are modulated by Slob expression level. Furthermore, Slob genotype influences action potential duration in vivo. This unprecedented combination of current-clamp, macroscopic-current, and single-channel recordings from neurons in brains of living flies defines a critical role for an ion channel modulatory protein complex in the control of neuronal excitability. We show further that Slob-null flies exhibit significantly longer lifespan than controls under conditions of complete food deprivation. Crosses with deficiency lines demonstrate that this enhanced resistance to starvation-induced death maps close to the slob locus. Together, these results indicate that Slob may serve a novel regulatory function in feeding behavior, possibly by influencing the excitability of the PI neurons.

Drosophila ortholog of succinyl-CoA synthetase {beta} subunit: a novel modulator of Drosophila KCNQ channels

Voltage-gated KCNQ potassium channels are responsible for slowly activating potassium currents in heart, brain, and other tissues. Functional defects of KCNQ channels are linked with many diseases, including epilepsy and cardiac arrhythmias. Therefore KCNQ potassium channels have been widely studied, especially in the CNS. We have identified Drosophila CG11963, which encodes a protein orthologous to the beta subunit of mammalian succinyl-CoA synthetase (SCS, also known as succinate thiokinase), as a novel modulator of Drosophila KCNQ channels. Direct interaction of CG11963 and dKCNQ was demonstrated by yeast two-hybrid screen and coimmunoprecipitation. Cell surface biotinylation experiments further confirmed that CG11963 resides on the plasma membrane of tsA-201 cells. Coexpression of CG11963 with dKCNQ shifts the conductance-voltage (G-V) relationship of dKCNQ channels to more positive membrane potentials in Chinese hamster ovary (CHO) cells. Moreover, directly dialyzing glutathione S-transferase fusion CG11963 protein into CHO cells also shifts the dKCNQ G-V curve rightward. The effect of CG11963 persists in the presence of 1 mM adenosine triphosphate (ATP), a substrate of SCS. Taken together, our data define CG11963 as a new dKCNQ-binding protein capable of modulating the properties of the channel. Our evidence suggests that this modulation is mediated by direct interaction of CG11963 with the channel and is not dependent on ATP.