Potent stimulation of large-conductance Ca2+-activated K+ channels by rottlerin, an inhibitor of protein kinase C-δ, in pituitary tumor (GH3) cells and in cortical neuronal (HCN-1A) cells
✍ Scribed by Sheng-Nan Wu; Ya-Jean Wang; Ming-Wei Lin
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 426 KB
- Volume
- 210
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Abstract
The effects of rottlerin, a known inhibitor of protein kinase C‐δ activation, on ion currents were investigated in pituitary tumor (GH~3~) cells. Rottlerin (0.3–100 µM) increased the amplitude of Ca^2+^‐activated K^+^ current (I~K(Ca)~) in a concentration‐dependent manner with an EC~50~ value of 1.7 µM. In intracellular perfusion with rottlerin (1 µM) or staurosporine (10 µM), phorbol 12‐myristate 13‐acetate‐induced inhibition of I~K(Ca)~ in these cells was abolished. In cell‐attached mode, rottlerin applied on the extracellular side of the membrane caused activation of large‐conductance Ca^2+^‐activated K^+^ (BK~Ca~) channels, and a further application of BAPTA‐AM (10 µM) to the bath had no effect on rottlerin‐stimulated channel activity. When cells were exposed to rottlerin, the activation curve of these channels was shifted to less positive potential with no change in the slope factor. Rottlerin increased BK~Ca~‐channel activity in outside‐out patches. Its change in kinetic behavior of BK~Ca~ channels is primarily due to an increase in mean open time. With the aid of minimal kinetic scheme, a quantitative description of rottlerin stimulation on BK~Ca~ channels in GH~3~ cells was also provided. Under current‐clamp configuration, rottlerin (1 µM) decreased the firing of action potentials. I~K(Ca)~ elicited by simulated action potential waveforms was enhanced by this compound. In human cortical HCN‐1A cells, rottlerin (1 µM) could also interact with the BK~Ca~ channel to stimulate I~K(Ca)~. Therefore, rottlerin may directly activate BK~Ca~ channels in neurons or endocrine cells. J. Cell. Physiol. 210: 655–666, 2007. © 2006 Wiley‐Liss, Inc.