Agonist-induced activation of a non-selective ion current in glomerular endothelial cells.
The control of intracellular calcium activity ([Ca2+]i) and membrane voltage (Vm) play an important role in regulating functions of glomerular endothelial cells (GEC). We investigated the effect of extracellular ATP on the intracellular [Ca2+]i, Vm and ion conductances in GEC. ATP (100 mumol/liter) induced a rapid increase of [Ca2+]i in GEC from 20 +/- 6 to 442 +/- 84 nmol/liter, which was followed by a sustained Ca2+ plateau of 112 +/- 29 nmol/liter. In a bath solution with a low extracellular Ca2+ concentration the ATP-induced [Ca2+]i peak was still present, but the [Ca2+]i plateau was completely prevented. In 186 experiments with the patch clamp technique the addition of ATP (1 to 100 mumol/liter) to GEC induced a transient small hyperpolarization, which was followed by a depolarization. During the ATP-induced depolarization an increase of the whole cell conductance was found. The Ca2+ ionophore A23187 (10 mumol/liter) mimicked the effect of ATP on Vm. Reduction of the extracellular Ca2+ to 1 mumol/liter itself depolarized GEC reversibly from -88 +/- 2 to -60 +/- 12 mV and increased the ATP-induced depolarization to -18 +/- 3 mV. In the absence of Na+ in the bathing solution (replacement by NMDG+) ATP induced only an attenuated depolarization and no inward current was activated. Flufenamate (100 mumol/liter), a blocker of non-selective ion channels inhibited the ATP-induced depolarization of Vm significantly by 58 +/- 13%, whereas nicardipine (10 mumol/liter) or amiloride (10 mumol/liter) had no effect. Our data indicate that the resting Vm of GEC cells is almost completely dominated by K+ conductances and that ATP activates a Ca2+ dependent non-selective ion conductance in GEC.
Pavenstädt
H
H
Department of Nephrology, Albert-Ludwigs-Universität Freiburg, Germany.
Henger
A
A
Briner
V
V
Fischer
K G
KG
Huber-Lang
M
M
Schollmeyer
P
P
Greger
R
R
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000032:analysis / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D018999:Charybdotoxin / Q000494:pharmacology; D002713:Chlorine / Q000502:physiology; D004727:Endothelium / Q000502:physiology; D005439:Flufenamic Acid / Q000494:pharmacology; D007473:Ion Channels / Q000502:physiology; D017136:Ion Transport; D007476:Ionophores / Q000494:pharmacology; D007678:Kidney Glomerulus / Q000502:physiology*; D008564:Membrane Potentials; D009529:Nicardipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000032:analysis; D012964:Sodium / Q000502:physiology; D013873:Thionucleotides / Q000494:pharmacology; D014544:Uridine Triphosphate / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007473:Ion Channels; D007476:Ionophores; D013873:Thionucleotides; D018999:Charybdotoxin; D000001:Calcimycin; D002713:Chlorine; D005439:Flufenamic Acid; D000584:Amiloride; D000255:Adenosine Triphosphate; D012964:Sodium; D009529:Nicardipine; D011188:Potassium; D002118:Calcium; D014544:Uridine Triphosphate; C008501:2-methylthio-ATP