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 Ca2+-activated K+ current (IK(Ca)) in a concentration-dependent manner with an EC50 value of 1.7 μM. In intracellular perfusion with rottlerin (1 μM) or staurosporine (10 μM), phorbol 12-myristate 13-acetate-induced inhibition of IK(Ca) in these cells was abolished. In cell-attached mode, rottlerin applied on the extracellular side of the membrane caused activation of large-conductance Ca2+-activated K+ (BKCa) 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 BKCa-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 BKCa channels in GH3 cells was also provided. Under current-clamp configuration, rottlerin (1 μM) decreased the firing of action potentials. IK(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 BKCa channel to stimulate IK(Ca). Therefore, rottlerin may directly activate BKCa channels in neurons or endocrine cells.
All Science Journal Classification (ASJC) codes
- Clinical Biochemistry
- Cell Biology