Patch Clamp on the Cape – interview with South African neuroscientist Joe Raimondo
- MCI visit neuroscientist Joe Raimondo’s lab at the University of Cape Town, SA
- Joe describes his group’s latest research investigating causes of brain seizures using electrophysiological, optical imaging and computational models
- Their findings reveal the importance of cation-chloride cotransporters in setting the chloride reversal potential
- Maintaining chloride driving force is fundamental for correct neuronal signalling
Our Joint Managing Director, Sias Jordaan, was lucky enough to be in Cape Town this December. Not content with the beach and sun, he and support application scientist Simone le Roux checked in on longtime customer – Joe Raimondo – at the University of Cape Town, SA.
Why do brains seize?
Joe is a South African Neuroscientist investigating a big question – why do brains seize? To get the answers, his lab uses a wide range of approaches: electrophysiological, optical imaging and computational models. With these techniques, they focus on how changes to inhibitory synaptic transmission and neuroinflammatory responses relate to the emergence and termination of epileptic seizures. You can learn more about the Raimondo lab here.
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Bringing Africa to the neuroscience technology table
Being based in Cape Town, Joe is also passionate about developing African capacity in cellular neurophysiology and computational neuroscience. For the last three years, his lab has hosted and organized the IBRO Simons Computational Neuroscience Imbizo. This is an initiative which brings world leaders in computational/theoretical neuroscience and machine learning to African students to impart their skills, knowledge and passion for what they do. Africa is a continent with a lot to contribute but often lacks the resources that many international labs boast. This workshop aims to begin to correct that imbalance and bring diverse points of view to the table.
Joe was kind enough to take Simone and Sias on a tour of his lab and chat to us about his lab’s most recent publication in eLife, Biophysical models reveal the relative importance of transporter proteins and impermeant anions in chloride homeostasis. You can see his answers to our questions below.
MCI: In your latest paper you use biophysical models and patch clamp experiments to explore the role of impermeant anions in chloride homeostasis. Can you explain chloride homeostasis and tell us the take-home message from your findings?
JR: One of the ways that neurons pass on information is through the flow of chloride ions. The force that moves chloride ions (AKA ‘chloride driving force’) into or out-of neurons depends mainly on two factors. First, chloride ions, like other particles, tend to move from an area where they are plentiful to areas where they are less abundant. Secondly, chloride ions are negatively charged and are therefore attracted to areas where the net charge (determined by the mix of positively and negatively charged particles) is more positive than their current position.
It was previously believed that a group of proteins known as cation-chloride cotransporters (CCCs), which transport chloride ions and positive ions together across the cell membrane, set the chloride driving force. However, it was recently suggested that negatively charged ions that are unable to cross the membrane (AKA impermeant anions) may set the driving force instead, by contributing to the net charge across the membrane. To explore these two possibilities, we used a computational model of the neuron.
In the simulations, altering the activity of the CCCs led to big changes in the chloride driving force, whereas changing impermeant anion levels altered the volume of cells, but not the chloride driving force. This was because the flow of chloride ions across the membrane led to a compensatory change in the net charge across the membrane. Patch-clamping in mice and rats was performed to confirm the model’s predictions.
Defects in controlling the chloride driving force in brain cells have been linked with epilepsy, stroke and other neurological diseases. Therefore, a better knowledge of these mechanisms may in future help to identify the best targets for drugs to treat such conditions.
MCI: In the paper, you performed perforated-patch recordings. You also performed single cell electroporation in vitro. Do you have any tips for our readers to help them perform these type of experiments?
JR: Yes, perforated patch-clamp recordings are technically very demanding and to have any chance of success one needs super-stable micromanipulators. The MCI manipulators were incredibly stable and helped make these experiments achievable.
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MCI: Why did you use organotypic slices in these experiments as opposed to acute slices?
JR: They require fewer animals as you can sacrifice one animal a week, instead of 1 every day for acute slices. This is ethically advantageous. They are also a well described and rather beautiful system to work in where one has extended in vitro experimental access to the tissue. For example, this allowed us to easily transfect slices with channelrhodopsin which was useful for our experiments.
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MCI: What is the future direction of this research?
JR: We plan to use our modeling framework, ie the pump-leak mechanism in tandem with electrodiffusion to investigate other fundamental properties of neuronal biophysics.
Read other interesting pieces about Neuroscience techniques at our blog.
Düsterwald, K. M., Currin, C. B., Burman, R. J., Akerman, C. J., Kay, A. R., & Raimondo, J. V. (2018). Biophysical models reveal the relative importance of transporter proteins and impermeant anions in chloride homeostasis. eLife, 7, e39575.