A novel type of internal barium block of a maxi-K+ channel from human vas deferens epithelial cells

Biophysical Journal
Y SohmaM A Gray

Abstract

We have recently shown that a maxi-K+ channel from vas deferens epithelial cells contains two Ba2+-binding sites accessible from the external side: a "flickering" site located deep in the channel pore and a "slow" site located close to the extracellular mouth of the channel. Using the patch-clamp technique, we have now studied the effect of internal Ba2+ on this channel. Cytoplasmic Ba2+ produced a voltage- and concentration-dependent "slow" type of block with a dissociation constant of approximately 100 microM. However, based on its voltage dependence and sensitivity to K+ concentration, this block was clearly different from the external "slow" Ba2+ block previously described. Kinetic analysis also revealed a novel "fast flickering" block restricted to channel bursts, with an unblocking rate of approximately 310 s(-1), some 10-fold faster than the external "flickering" block. Taken together, these results show that this channel contains multiple Ba2+-binding sites within the conduction pore. We have incorporated this information into a new model of Ba2+ block, a novel feature of which is that internal "slow" block results from the binding of at least two Ba2+ ions. Our results suggest that current models for Ba2+ block of maxi...Continue Reading

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Citations

Feb 21, 2006·The European Journal of Neuroscience·H HayasakiM Watanabe
Dec 30, 2011·American Journal of Physiology. Regulatory, Integrative and Comparative Physiology·Fumiya FurukawaToyoji Kaneko
Jan 25, 2000·American Journal of Physiology. Heart and Circulatory Physiology·H ShiZ Wang

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