BA-2+ RELEASE FROM SODA GLASS MODIFIES SINGLE MAXI K+-CHANNEL ACTIVITY IN PATCH CLAMP EXPERIMENTS

The gating properties of maxi K+ channels from Necturus gallbladder epithelium depend on whether borosilicate glass (BG) or blue tip hematocrit glass (SG) is used to construct the patch pipettes. The data are consistent with solubilization from SG of a component which exerts voltage-dependent, cytosolic-side specific block, closely resembling "slow block" by Ba2+ ions. Ringer's solution preincubated with SG, but not with BG, blocked inside-out maxi K+ channels when used as bathing solution. Mass spectrometry revealed that Ba2+ is released by the glass from fast and slow-release compartments (SG contains 3% wt/wt BaO), and is the only ion found in the solution at concentrations consistent with the observed channel block. Additionally, SG released O2-, Na+, Ca2+, and Mg2+, all to micromolar concentrations. These elements do not interfere with maxi K+ channels but they could in principle alter the properties of other ion channels. Thus, screening for channel-modifying substances released by the glass may be necessary for the adequate interpretation of patch-clamp results.