Figure 4. Determination of [Ca2+]i dependence of TRPM2 opening and closing rates. (A) Two representative current traces from patches with smaller numbers of TRPM2 channels superfused with various test [Ca2+]i (bars) in the presence of 32 µM ADPR. Pipette [Ca2+] was ∼4 µM. (left) The number of channels (N) in test segments at low micromolar Ca2+ (blue bars; expanded below) was obtained by linear interpolation of N in bracketing segments at saturating Ca2+. (right) Test segments for [Ca2+]i >40 µM were defined as the time periods between two occurrences of irreversible channel closure (red arrows). Within such segments (blue bars; expanded below) Po approached unity and N was given by the maximum current level. (B) Closing rate at various submicromolar [Ca2+]i was studied in a macropatch; in the presence of 32 µM ADPR TRPM2 channels were alternately exposed to 125 µM Ca2+ and various submicromolar test [Ca2+] (bars); pipette [Ca2+] was ∼4 µM. Current decay time courses in various test [Ca2+]i were fitted by single exponentials (colored smooth lines and time constants [in milliseconds]); those in 8 nM (blue), 300 nM (black), and 4.4 µM Ca2+ (red) are shown below at an expanded time scale. Note the complete lack of reopening events in 8 and 300 nM Ca2+; in 4.4 µM Ca2+ opening rate is still far smaller than closing rate as witnessed by the small remaining steady-state current.
Image published in: Csanády L and Törocsik B (2009)
© 2009 Csanády and Törőcsik. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike license
Permanent Image Page
Printer Friendly View
XB-IMG-123581