Figure 5.

Rundown prevents UDP from locking K_ATP channels within intraburst transitions. (A) Single K_ATP channel records during partial rundown in the absence (top) and presence (bottom) of 1 mM UDP. Zero-current level indicated by 0 pA. (B) Intraburst kinetic properties. UDP (right) did not affect distributions of closed (top) and open (bottom) times within bursts of channel activity. Both distributions were well-fitted by single exponents, with τ_c,1 and τ_o representing characteristic closed and open times, respectively. (C) Distribution of gaps between bursts in the absence (left) and presence (right) of UDP. Under both conditions, distributions needed to be fitted by the sum of two exponents with characteristic times τ_c,2 andτ_c,3. Solid lines correspond to the sum of both exponents drawn by fitting, whereas dashed lines correspond to individual exponents. Holding potential was −60 mV. (D) Kinetic scheme constructed based on calculated rates of transitions (in s⁻¹, Eq. 8) in the absence (left) and presence (right) of 1 mM UDP.