Existence, properties, and functional expression of “Maxi-K”-type, Ca2+-activated K+ channels in short-term cultured hepatocytes
✍ Scribed by Darlene C. Pon; Ceredwyn E. Hill
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 218 KB
- Volume
- 171
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
A large-conductance, Ca 2/ -activated K / channel was identified and characterized in embryonic chick hepatocytes using the patch-electrode voltage-clamp technique. The channel conductance was 213 pS in excised patches bathed in symmetrical 145 mM KCl and 1 mM Ca 2/ . Current-voltage relationships were linear with high K / on both sides of the membrane but showed constant field rectification as the K / gradient was increased. The reversal potential shifted 58 mV per 10-fold change in the ratio of external to internal K / . Channel openings occurred at potentials higher than /50 mV in cell-attached patches. The open probability 1 voltage relationship shifted to more negative potentials in excised, inside-out patches exposed to a solution containing high Ca 2/ . The voltage sensitivity of the channel was not significantly affected by changes in internal Ca 2/ concentration. Conversely, channel gating, reflected in the half-activation potential, shifted 118 mV per 10-fold change in internal Ca 2/ at concentrations less than Ç2 mM, although at higher Ca 2/ , this parameter was Ca 2/ insensitive. Channel open probability in cell-attached patches increased significantly following exposure of the cells to either the Ca 2/ ionophore A-23187 or L-alanine, a cell-volume modulator. Channel density increased with time spent in culture from no observations in 10-hr cells, through 13 and 80% of patches in 24-and 48-hr cultured cells, respectively. The implications of delayed functional expression for ion channel studies in acutely dissociated cells is discussed.