![Figure 3. Measuring iCa in physiological ionic conditions. (A) Linear fits (green and red lines) to selected Iopen and Iclosed data (plotted in green and pink, respectively) from 25 Vapp ramps recorded from an excised lum-out nuclear membrane patch containing one active InsP3R channel under symmetric ionic conditions, with pipette and perfusion solutions containing 140 mM KCl, 0.5 mM MgCl2, and 3 µM [Ca2+]f. Pipette solution contained 2 µM InsP3. (B) Graph of the fitted Iopen-Vapp and Iclosed-Vapp lines in the I-Vapp region marked by the black rectangle in A. Zero-current level (black dotted line) established at the intersection of the I-Vapp fits at Vapp = 0 (marked by orange arrowhead). (C) Linear fits to Iopen and Iclosed data (same convention as in A) from 25 Vapp ramps recorded for the same membrane patch under asymmetric ionic conditions, with perfusion solution containing 2 mM CaCl2. I and Vapp ranges in A and C are the same. (D) Graph of the fitted I-Vapp lines in the same I-Vapp region with the same zero-current level as in B. Vapp = 0 (marked by orange arrowhead) at the intersection of the Iclosed-Vapp line and zero-current level. iCa is Iopen at Vapp = 0 (marked by blue arrow).](https://cdn.rupress.org/rup/content_public/journal/jgp/136/6/10.1085_jgp.201010513/5/jgp_201010513_rgb_fig3.jpeg?Expires=1773550511&Signature=t6OKyxlSgv2qHbXCdq1WmQ~3ZvNhtEzIUweofj58IWJ15~dr30P8SQxaq-m1mlkH~Qx5MWuGIq9UzBTFDqV98K4hK-2dQrnls2RcvAOu4RJp~yC-u2BPGXmnQF~HvhA20SAR2ShDC37Nh2zdAk8Py8OxYjqBc-3xQNzTkYc15qd1ltvaBz7B-Of40RMYv0OwyIl39LxJ8PToGX6c23vMfFZWZgC~U7F-1w-U56acSQhj9MMkFUv5HS9snKL6uTI4oXZeHccl6RT3aMEWRSc6Bp7yCThvs5TWub2tZ-38Zis3aiCtSHFuUN1Jbyfz62kaTOC6D8LRe2eLWZ2w6xpaAA__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
Measuring iCa in physiological ionic conditions. (A) Linear fits (green and red lines) to selected Iopen and Iclosed data (plotted in green and pink, respectively) from 25 Vapp ramps recorded from an excised lum-out nuclear membrane patch containing one active InsP3R channel under symmetric ionic conditions, with pipette and perfusion solutions containing 140 mM KCl, 0.5 mM MgCl2, and 3 µM [Ca2+]f. Pipette solution contained 2 µM InsP3. (B) Graph of the fitted Iopen-Vapp and Iclosed-Vapp lines in the I-Vapp region marked by the black rectangle in A. Zero-current level (black dotted line) established at the intersection of the I-Vapp fits at Vapp = 0 (marked by orange arrowhead). (C) Linear fits to Iopen and Iclosed data (same convention as in A) from 25 Vapp ramps recorded for the same membrane patch under asymmetric ionic conditions, with perfusion solution containing 2 mM CaCl2. I and Vapp ranges in A and C are the same. (D) Graph of the fitted I-Vapp lines in the same I-Vapp region with the same zero-current level as in B. Vapp = 0 (marked by orange arrowhead) at the intersection of the Iclosed-Vapp line and zero-current level. iCa is Iopen at Vapp = 0 (marked by blue arrow).
