The key facts

  • BK channels pass potassium ions 10-20 times more easily than other potassium channels; conductance increases as a species is evolutionarily closer to mammals.
  • Weak channels have to be opened in greater numbers, they compete for calcium, and the moment of spike onset 'drifts'.
  • The model was tested only on cerebellar Purkinje cells and was acknowledged by the authors as simplified.

A possible answer to a long-standing question in neuroscience

Since the early 1980s, neuroscientists have tried to understand why nerve cells need BK channels (Big Potassium), which pass potassium ions 10-20 times more easily than any other channels of this type. A possible answer was found by a team from the Okinawa Institute of Science and Technology led by Erik De Schutter; the results were published in the journal Communications Biology. Nerve cells exchange short electrical discharges — spikes — and the precision of their synchronization underlies movement control, memory, and sensory processing. The structure of BK channels has long been described, yet their evolutionary purpose remained unclear. Moreover, conductance varied between species: the most powerful channels are found in mammals and birds, while in mollusks and insects they are noticeably weaker.

Evolutionary tree and modeling

De Schutter, together with evolutionary biologists Thomas Bourguignon and Simon Hellemans, mapped BK channel conductance onto the evolutionary tree of animals, relying on genomic data and previous measurements: the closer a species is to mammals, the more powerful its channels. Then, in the molecular modeling program STEPS, the researchers reproduced the operation of channels of different power levels taking into account calcium concentration — four of its ions open each BK channel.

The trap of weak channels

The calculations revealed a 'trap' of weak channels: to pass the same amount of potassium, far more of them have to be opened, causing them to compete with each other for calcium, which is in short supply. The powerful channels of birds and mammals face no such problem. With weak conductance, the moment of spike onset is also blurred — the time of its birth 'drifts'. 'We suggest that it was precisely the precision of spike timing that became the key evolutionary pressure driving the increase in channel conductance in mammals. As movements became more complex, sub-millisecond precision became necessary,' De Schutter explained.

Limitations and significance of the work

The authors acknowledge that the model is simplified: channel operation was tested on only one type of neuron — cerebellar Purkinje cells, which are involved in movement control. Since BK channels occur in many tissues and influence, for example, muscle contraction, the findings may prove useful not only to neuroscientists but also to cell biologists and evolutionary biologists.