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Structural requirements for differential sensitivity of KCNQ K+ channels to modulation by Ca2+/calmodulin

By Nikita Gamper, Yang Li and Mark S. Shapiro


Calmodulin modulation of ion channels has emerged as a prominent theme in biology. The sensitivity of KCNQ1–5 K � channels to modulation by Ca 2 � /calmodulin (CaM) was studied using patch-clamp, Ca 2 � imaging, and biochemical and pharmacological approaches. Coexpression of CaM in Chinese hamster ovary (CHO) cells strongly reduced currents of KCNQ2, KCNQ4, and KCNQ5, but not KCNQ1 or KCNQ3. In simultaneous current recording/Ca 2 � imaging experiments, CaM conferred Ca 2 � sensitivity to KCNQ4 and KCNQ5, but not to KCNQ1, KCNQ3, or KCNQ1/KCNE1 channels. A chimera constructed from the carboxy terminus of KCNQ4 and the rest KCNQ1 displayed Ca 2 � sensitivity similar to KCNQ4. Chimeras constructed from different lengths of the KCNQ4 carboxy terminal and the rest KCNQ3 localized a region that confers sensitivity to Ca 2 � /CaM. Lobe-specific mutations of CaM revealed that its amino-terminal lobe mediates the Ca 2 � sensitivity of the KCNQ/CaM complex. The site of CaM action within the channel carboxy terminus overlaps with that of the KCNQ opener N-ethylmaleimide (NEM). We found that CaM overexpression reduced NEM augmentation of KCNQ2, KCNQ4, and KCNQ5, and NEM pretreatment reduced Ca 2 � /CaM-mediated suppression of M current in sympathetic neurons by bradykinin. We propose that two functionally distinct types of carboxy termini underlie the observed differences among this channel family

Topics: KCNQ2, 3, 5, cardiac (IKs, KCNQ1, epithelial (KCNQ1) and
Year: 2005
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