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. 1998 Jan;74(1):199–209. doi: 10.1016/S0006-3495(98)77780-X

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

Y Sohma 1, A Harris 1, B E Argent 1, M A Gray 1
PMCID: PMC1299375  PMID: 9449323

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-K+ channels need to be revised.

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Selected References

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