Intracellular Na(+) modulates large conductance Ca(2+)-activated K (+) currents in human umbilical vein endothelial cells.
We studied the effects of Na(+) influx on large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels in cultured human umbilical vein endothelial cells (HUVECs) by means of patch clamp and SBFI microfluorescence measurements. In current-clamped HUVECs, extracellular Na(+) replacement by NMDG(+) or mannitol hyperpolarized cells. In voltage-clamped HUVECs, changing membrane potential from 0 mV to negative potentials increased intracellular Na(+) concentration ([Na(+)](i)) and vice versa. In addition, extracellular Na(+) depletion decreased [Na(+)](i). In voltage-clamped cells, BK(Ca) currents were markedly increased by extracellular Na(+) depletion. In inside-out patches, increasing [Na(+)](i) from 0 to 20 or 40 mM reduced single channel conductance but not open probability (NPo) of BK(Ca) channels and decreasing intracellular K(+) concentration ([K(+)](i)) gradually from 140 to 70 mM reduced both single channel conductance and NPo. Furthermore, increasing [Na(+)](i) gradually from 0 to 70 mM, by replacing K(+), markedly reduced single channel conductance and NPo. The Na(+)-Ca(2+) exchange blocker Ni(2+) or KB-R7943 decreased [Na(+)](i) and increased BK(Ca) currents simultaneously, and the Na(+) ionophore monensin completely inhibited BK(Ca) currents. BK(Ca) currents were significantly augmented by increasing extracellular K(+) concentration ([K(+)](o)) from 6 to 12 mM and significantly reduced by decreasing [K(+)](o) from 12 or 6 to 0 mM or applying the Na(+)-K(+) pump inhibitor ouabain. These results suggest that intracellular Na(+) inhibit single channel conductance of BK(Ca) channels and that intracellular K(+) increases single channel conductance and NPo.
Liang
Guo Hua
GH
Department of Physiology, Ewha Womans University, Yang Chun-gu, Seoul, Republic of Korea.
Kim
Moon Young
MY
Park
Seonghee
S
Kim
Ji Aee
JA
Choi
Shinkyu
S
Suh
Suk Hyo
SH
D002478:Cells, Cultured; D004594:Electrophysiology; D042783:Endothelial Cells / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism / Q000502:physiology; D007476:Ionophores / Q000494:pharmacology; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects*; D008564:Membrane Potentials / Q000502:physiology; D008985:Monensin / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000502:physiology; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology; D014471:Umbilical Veins / Q000378:metabolism / Q000502:physiology*
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D004791:Enzyme Inhibitors; D007476:Ionophores; D051036:Large-Conductance Calcium-Activated Potassium Channels; D019831:Sodium-Calcium Exchanger; D008985:Monensin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D013890:Thiourea; D011188:Potassium