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 (EM), simultaneously. The tip of the triple-barreled assembly was made less than 0.6 .mu.m in outside diameter. Prior to in vivo measurements, some physicochemical properties of microelectrodes were examined in vitro for the slope constant, selectively 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 [Rana catesbeiana] in vivo, the following results were obtained: In sartorius muscle, the average (Na)i was 14.8 meq/l, the (K)i of 64.5 meq/l and the EM-68.2 mV. In proximal tubule cells, the average (Na)i, (K)i and EM were 16.8, 63.0 meq/l and -65.9 mV, respectively. There were significant correlations in the proximal tubule between (K)i and EM, 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. Several problems inhert in the multibarreled microelectrode were discussed from the practical point of view.