Intrinsic gating of inward rectifier in bovine pulmonary artery endothelial cells in the presence or absence of internal Mg2+.
Inward rectifier (IR) currents were studied in bovine pulmonary artery endothelial cells in the whole-cell configuration of the patch-clamp technique with extracellular K+ concentrations, [K+]o, ranging from 4.5 to 160 mM. Whether the concentration of free Mg2+ in the intracellular solution, [Mg2+]i, was 1.9 mM or nominally 0, the IR exhibited voltage- and time-dependent gating. The IR conductance was activated by hyperpolarization and deactivated by depolarization. Small steady-state outward IR currents were present up to approximately 40 mV more positive than the K+ reversal potential, EK, regardless of [Mg2+]i. Modeled as a first-order C in equilibrium O gating process, both the opening rate, alpha, and the closing rate, beta, were exponentially dependent on voltage, with beta more steeply voltage dependent, changing e-fold for 9 mV compared with 18 mV for an e-fold change in alpha. Over all [K+]o studied, the voltage dependence of alpha and beta shifted along with EK, as is characteristic of IR channels in other cells. The steady-state voltage dependence of the gating process was well described by a Boltzmann function. The half-activation potential was on average approximately 7 mV negative to the observed reversal potential in all [K+]o regardless of [Mg2+]i. The activation curve was somewhat steeper when Mg-free pipette solutions were used (slope factor, 4.3 mV) than when pipettes contained 1.9 mM Mg2+ (5.2 mV). The simplest interpretation of these data is that IR channels in bovine pulmonary artery endothelial cells have an intrinsic gating mechanism that is not due to Mg block.
Department of Medicine, Rush Medical Center, Chicago, Illinois 60612.
M R
MR
Silver
T E
TE
DeCoursey
D000818:Animals; D002417:Cattle; D004058:Diffusion; D004594:Electrophysiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000502:physiology*; D007700:Kinetics; D008274:Magnesium / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D015221:Potassium Channels / Q000502:physiology; D011651:Pulmonary Artery / Q000166:cytology / Q000502:physiology
D015221:Potassium Channels; D008274:Magnesium