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.
Silver
M R
MR
Department of Medicine, Rush Medical Center, Chicago, Illinois 60612.
DeCoursey
T E
TE
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