A new solid-state microelectrode for measuring intra-cellular chloride activities

Solid-state microelectrodes for measuring intracellular Cl^? activity (aⁱCl) were made by sealing the tips of tapered glass capillaries (tip diameter 0.3 μm), coating them under vacuum with a 0.2–0.3 μm thick layer of spectroscopic grade silver, and sealing them (except for the terminal 2–5 μm of the tip) inside tapered glass shields. 106 microelectrodes had an average slope of 55.0 ± 0.6 mV (S.E.) per decade change in α_Cl. Tip resistance was (77.1 ± 3.1 × 10⁹ω (n=30). Electrode response was rapid (10–20 s), was unaffected by HCO₃^?, H₂PO₄^2? or protein, and remained essentially unchanged over a 24-h period. αⁱ_Cl in frog sartorius muscle fibers and epithelial cells of bullfrog small intestine was measured in vitro. In both tissues, αⁱ_Cl significantly exceeded the value corresponding to equilibrium distribution of Cl^? across the cell membrane.