Regulatory effect of sulphatides on BKCa channels

Background and purpose: Sulphatides are sulphated glycosphingolipids expressed on the surface of many cell types, particularly neurones. Changes in sulphatide species or content have been associated with epilepsy and Alzheimer's disease. As the large conductance, calcium sensitive K+ channel (BKCa) are modulated by membrane lipids, the aim of the study was to explore possible effects of sulphatides on BKCa channels. Experimental approach: Using patch-clamp techniques, we studied effects of exogenous sulphatides on BKCa channels expressed in Chinese hamster ovary cells. Key results: Sulphatides reversibly increased the whole-cell current and the single channel open probability of BKCa channels dose-dependently. The EC50 value on the channel at +10 mV was 1.6 mu M and the Hill coefficient was 2.5. In inside-out patches, sulphatides increased the single channel open probability from both intra- and extra-cellular faces of the membrane, but more effectively with external application. Furthermore, activation of the channels by sulphatides was independent of intracellular Ca2+ concentration. Sulphatides also shifted the activation curve of the channels to less positive membrane potentials. Mutant BKCa channels lacking a 59 aminoacid region important for amphipath activation (STREX) were less activated by the sulphatides. Conclusions and Implications: Sulphatides are novel activators of BKCa channels, independent of intracellular Ca2+ or other signalling molecules but partly dependent on the STREX sequence of the channel protein. As changes of sulphatide content are associated with neuronal dysfunction, as in epilepsy and Alzheimer's disease, our results imply that these effects of sulphatides may play important pathophysiological roles in regulation of BKCa channels.