Effects of external Rb+ on inward rectifier K+ channels of bovine pulmonary artery endothelial cells.
Inward rectifier (IR) K+ channels of bovine pulmonary artery endothelial cells were studied using the whole-cell, cell-attached, and outside-out patch-clamp configurations. The effects of Rb+ on the voltage dependence and kinetics of IR gating were explored, with [Rb+]o + [K+]o = 160 mM. Partial substitution of Rb+ for K+ resulted in voltage-dependent reduction of inward currents, consistent with Rb+ being a weakly permeant blocker of the IR. In cells studied with a K(+)-free pipette solution, external Rb+ reduced inward IR currents to a similar extent at large negative potentials but block at more positive potentials was enhanced. In outside-out patches, the single-channel i-V relationship was approximately linear in symmetrical K+, but rectified strongly outwardly in high [Rb+]o due to a reduced conductance for inward current. The permeability of Rb+ based on reversal potential, Vrev, was 0.45 that of K+, whereas the Rb+ conductance was much lower, 0.034 that of K+, measured at Vrev-80 mV. The steady state voltage-dependence of IR gating was determined in Rb(+)-containing solutions by applying variable prepulses, followed by a test pulse to a potential at which outward current deactivation was observed. As [Rb+]o was increased, the half-activation potential, V1/2, changed less than Vrev. In high [K+]o solutions V1/2 was Vrev-6 mV, while in high [Rb+]o V1/2 was Vrev + 7 mV. This behavior contrasts with the classical parallel shift of V1/2 with Vrev in K+ solutions. Steady state IR gating was less steeply voltage-dependent in high [Rb+]o than in K+ solutions, with Boltzmann slope factors of 6.4 and 4.4 mV, respectively. Rb+ decreased (slowed) both activation and deactivation rate constants defined at V1/2, and decreased the steepness of the voltage dependence of the activation rate constant by 42%. Deactivation of IR channels in outside-out patches was also slowed by Rb+. In summary, Rb+ can replace K+ in setting the voltage-dependence of IR gating, but in doing so alters the kinetics.
Silver
M R
MR
Department of Medicine, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612.
Shapiro
M S
MS
DeCoursey
T E
TE
D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004573:Electrolytes / Q000378:metabolism; D004594:Electrophysiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects*; D007700:Kinetics; D010539:Permeability; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011651:Pulmonary Artery / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism / Q000494:pharmacology*
D004573:Electrolytes; D015221:Potassium Channels; D012413:Rubidium