Single-channel recordings were made using cell-free membrane patches (outside-out configuration) isolated from pheochromocytoma PC12 cells. ATP (50 μM) activated single channel currents in the isolated patches and the currents inactivated with a half-decay time of about 5 s. The single channel conductance was about 13 pS in external solution with 140 mM Na. The amplitudes of the single-channel currents were decreased when external Ca was increased from 1.8 to 16.2 mM, suggesting that Ca blocks ion permeation through the channel. These properties of single-channel currents may underlie those of the macroscopic current.
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