A Triple-barreled Microelectrode for Simultaneous Measurements of Intracellular Na⁺ and K⁺ Activities and Membrane Potential in Biological Cells

Abstract

A triple-barreled Na⁺, K⁺-selective microelectrode was constructed with liquid ion exchangers for Na⁺ (monensin) and K⁺ (Corning #477317) to measure the intracellular Na⁺ and K⁺ activities ((Na) _i and (K) _i) of a single cell and its membrane potential (E_M), simultaneously. The tip of the triple-barreled assembly was made less than 0.6μm in outside diameter.
Prior to in vivo measurements, some physicochemical properties of microelectrodes were examined in vitro for the slope constant, selectivity coefficient, electrical resistance, and pH effect, as well as measurements of the activity coefficient of ions in blood serum and Ringer solution.
Carrying out direct micropunctures on single cells of the sartorius muscle and renal proximal tubule of bullfrogs in vivo, we obtained the following results:(1) In sartorius muscle, the average (Na)_i was 14.8mEq/liter, the (K)_i 64.5mEq/liter, and the E_M -68.2mV.(2) In proximal tubule cells, the average (Na)_i, (K)_i and E_M were 16.8, 63.0mEq/liter and -65. 9mV, respectively.(3) There were significant correlations in the proximal tubule between (K)_i and E_M, and inversely between (Na)_i and EM, and between (Na)_i and (K)_i.These facts may somehow be related to both the activity of Na⁺ -K⁺ exchange pump and the osmotic equilibrium of water across the membrane.
Further, several problems inherent in the multibarreled microelectrode were discussed from the practical point of view.