Properties of single voltage‐dependent K + channels in dendrites of CA1 pyramidal neurones of rat hippocampus

Voltage‐dependent K + channels in the apical dendrites of CA1 pyramidal neurones play important roles in regulating dendritic excitability, synaptic integration, and synaptic plasticity. Using cell‐attached, voltage‐clamp recordings, we found a large variability in the waveforms of macroscopic K + currents in the dendrites. With single‐channel analysis, however, we were able to identify four types of voltage‐dependent K + channels and we categorized them as belonging to delayed‐rectifier, M‐, D‐, or A‐type K + channels previously described from whole‐cell recordings. Delayed‐rectifier‐type K + channels had a single‐channel conductance of 19 ± 0.5 pS, and made up the majority of the sustained K + current uniformly distributed along the apical dendrites. The M‐type K + channels had a single‐channel conductance of 11 ± 0.8 pS, did not inactivate with prolonged membrane depolarization, deactivated with slow kinetics (time constant 100 ± 6 ms at −40 mV), and were inhibited by bath‐applied muscarinic agonist carbachol (10 μ m ). The D‐type K + channels had a single‐channel conductance of around 18 pS, and inactivated with a time constant of 98 ± 4 ms at +54 mV. The A‐type K + channels had a single‐channel conductance of 6 ± 0.6 pS, inactivated with a time constant of 23 ± 2 ms at +54 mV, and contributed to the majority of the transient K + current previously described. These results suggest both functional and molecular complexity for K + channels in dendrites of CA1 pyramidal neurones.