Potassium Channels of the Lamprey Erythrocyte Membrane Exhibit a High Selectivity to K+ over Rb+: a Comparative Study of 86 Rb and

In older to assess the specificity of potassium channels, we examined the K+ transpoit pathways in the lampiey red blood cells using 8RRb and stable isotope 41K as tiaceis measured by the mass spectrometiic method Upon replacing 4 mmol/1 K+ with 4 mmol/1 Rb+ in the incubation medium, the iate coefficient foi unidirectional 86Rb influx (A"m) was significantly reduced from 1 48 ± 0 10 h _1 to 0 82 ±0 05 h -1 (P < 0 001) Addition of 1 mmol/1 Ba2+ to the incubation medium significantly decieased 86Rb influx m K+- (by 53%) and Rb+-media (by 26%) Thus, the i eduction in the late coefficient foi 80Rb influx in Rb +-medium as compaied to K +-modium was mainly due to the Ba2+-sensitive component (0 23 ± 0 04 vs 0 78 ± 0 10 h -1 , P < 0 001) The ouabain-sensitive component of 8eRb influx was also highei in K+-(A m = 0 62 ±0 05 h"1) than in Rb+-medmm (A'ln = 0 54 ± 0 05 h -1 , P < 0 05) In the piesence of 4 mmol/1