Effects of external tetraethylammonium ions and quinine on delayed rectifying K+ channels in mouse pancreatic beta‐cells.

Abstract

1. The whole-cell and outside-out patch configurations of the patch-clamp technique were used to study the mechanisms of block produced by external tetraethylammonium ions (TEA+) and quinine on delayed rectifying K+ channels in mouse pancreatic beta-cells. 2. In whole-cell recordings, TEA+ blocks the delayed outward current (which reflects the activity of delayed rectifying K+ channels by greater than 85%) in a concentration-dependent manner. The block appeared to be 1:1 with a Kd of approximately 1.4 mM at a membrane potential of 0 mV. The value of Kd varied with the membrane potential and there was an e-fold increase for a 70 mV depolarization. 3. Single-channel recordings revealed that delayed rectifying K+ channels have a unitary conductance of 8.5 pS ([K+]1 = 155 mM; [K+]o = 5.6 mM) and a single-channel K+ permeability of 2.8 X 10(-14) cm3 s-1. 4. First latency histograms of channel openings during voltage pulses from -70 to 0 mV peaked after 4 ms. A reaction scheme involving two closed states adequately but not perfectly described the distribution of the first latencies. The openings of the channels were grouped in bursts and the distribution of the closed times required two exponentials with time constants of 2.0 and 13 ms, respectively. The distribution of the open times could be described by a single exponential with a time constant of 25 ms. 5. Channel block produced by TEA+ (1 mM) was associated with a 40% decrease of the single-channel current amplitudes and a red…