Potassium conductance block by barium in amphibian Müller cells

The effect of barium on Müller cell K⁺ conductance was evaluated in the tiger salamander using enzymatically dissociated cells and cells in situ (retinal slice and isolated retina). Barium effects were similar in both cases. In dissociated cells, 50 μM Ba²⁺ depolarized cells 14.7 mV and raised cell input resistance from a control value of 16.0 to 133 MΩ. For cells in situ, 50 μM Ba²⁺ depolarized cells 6.9 mV and raised cell resistance from 12.5 to 50.4 MΩ. At corresponding Ba²⁺ concentrations, the resistance of cells in situ was somewhat lower than was the resistance of dissociated cells, a phenomenon that may be due to the small degree of electrical coupling present between Müller cells in situ. There was a similar positive correlation between the magnitude of Ba²⁺ -induced depolarization and input resistance in both dissociated cells and in situ cells. The magnitude of depolarizations generated by localized K⁺ ejections onto Müller cells was reduced substantially by Ba²⁺. These observations indicate that Ba²⁺ is an effective K⁺ channel blocker in Müller cells in situ as well as in enzymatically dissociated cells.