Two different store-operated Ca2+ entry pathways in MDCK cells.
Whole cell patch clamp experiments in conjunction with Fura-2 fluorescence microscopy were performed to study the mechanisms of 'store-operated' (capacitative) Ca2+ entry. In MDCK cells, depletion of inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ stores activates a store-operated cation current (SOCC) predominantly selective for Ca2+ than for Na+ or Mn2+ [Delles C., Haller T., Dietl P. A highly calcium-selective cation current activated by intracellular calcium release in MDCK cells. J Physiol 1995, 486: 557-569]. In the presence of extracellular Ca2+, thapsigargin (TG) stimulated both SOCC and a Ca(2+)-dependent K+ current (IK(Ca)), reflecting stimulation of store-operated Ca2+ entry. The Ca2+ entry blocker 1-[3-(4-methoxyphenyl) propoxyl]-1-(4-methoxyphenyl)-ethyl-1H-imidazole HCI (SK&F96365; 30 microM) did not inhibit SOCC. At the same concentration, it exerted a transient partial inhibition on IK(Ca) activated by TG-induced Ca2+ entry. It did, however, not directly inhibit IK(Ca). This was demonstrated by an unchanged relationship between the cytosolic Ca2+ concentration ([Ca2+]i) and IK(Ca) in experiments where [Ca2+]i was measured under whole cell patch clamp conditions and by a lacking effect of SK&F96365 on IK(Ca) prestimulated by a high 'clamped' [Ca2+]i. La3+ partially, but not directly, inhibited the TG-induced IK(Ca) at a concentration (10 microM) sufficient to entirely block SOCC. La3+ and SK&F96365 in combination exerted an additive reduction on the TG-induced whole cell conductance (G) and completely blocked IK(Ca) stimulated by TG. We conclude that two Ca2+ entry pathways with different pharmacological and biophysical properties are involved in 'store-operated' Ca2+ entry in MDCK cells.
Dietl
P
P
Department of Physiology, University of Innsbruck, Austria. paul.dietl@ulbk.ac.at
Haller
T
T
Wirleitner
B
B
Friedrich
F
F
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured / Q000378:metabolism*; D004285:Dogs; D004553:Electric Conductivity; D007093:Imidazoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007093:Imidazoles; D015221:Potassium Channels; D019284:Thapsigargin; D007811:Lanthanum; D015544:Inositol 1,4,5-Trisphosphate; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole