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. 2013 Jul 26;2(9):941–951. doi: 10.1242/bio.20135215

Fig. 3. Comparison of voltage-dependent K+ current in LNCaP cells with T-type Ca2+ current different expression levels (A) Ca2+-dependency of voltage-dependent K+ current in LNCaP-CTL cells.

Fig. 3.

(A) (a) Typical membrane currents at −30 and +100 mV in the presence of either 10 or 0.1 mM EGTA in the patch-pipette. (A) (b) Average i–v curves obtained in the presence of either 10 or 0.1 mM EGTA in the patch-pipette. (A) (c) Typical i–v curves obtained using ramp protocols show that increasing intracellular Ca2+ concentration shifts the i–v curve towards negative potentials. Left panel: intracellular perfusion of 400 nM Ca2+. Perfusing high concentration of Ca2+ into the cells was carried out using an EGTA-buffered solution in the patch-pipette (10 mM EGTA, 6.5 mM CaCl2 and 1 mM MgCl2). After breaking into whole-cell configuration, this solution shifted the i–v curve towards negative membrane potentials (WCR: current recorded just after breaking into whole-cell recording configuration, WCR+5 min: current recorded 5 minutes later). Right panel: bath perfusion with ionomycin (Iono, 1 µM), results in an increased K+ current and its shift to more negative membrane potentials. (B) In LNCaP-CTL cells that do not display any T-type Ca2+ current, no K+ current was observed for membrane potentials lower than 0 mV. Top panel: membrane current. Middle panel: pulse protocol. Bottom panel: I/V curve. (C) In LNCaP cells that express T-type Ca2+ current, here a LNCaP-NE cell, this transient Ca2+ current was followed by potassium current that could be observed for membrane potential ranging from −40 to 0 mV. (D) Similar results were observed for LNCaP cells stably overexpressing Cav3.2 channels (LNCaP-α1H). (E) In LNCaP-α1H cells, the K+ current was larger when EGTA was reduced in the patch-pipette (0.1 vs 10 mM EGTA). (F) Representation of relative membrane conductance (G/Gmax) in LNCaP cells displaying (T-type (+)) or not (T-type (−)) T-type Ca2+ current with 0.1 and 10 mM EGTA in the patch-pipette. (G) Representation of the relative membrane conductance (G/Gmax) in LNCaP-α1H cells with 0.1 and 10 mM EGTA in the patch-pipette.