Ion channel diversity, channel expression and function in the choroid plexuses

Two K+ conductances have been identified in the choroid plexus: Kv1 channel subunits mediate outward currents at depolarising potentials; Kir 7.1 carries an inward-rectifying conductance at hyperpolarising potentials. Both K+ channels are localised at the apical membrane where they may contribute to maintenance of the membrane potential while allowing the recycling of K+ pumped in by Na+-K+ ATPase. Two anion conductances have been identified in choroid plexus. Both have significant HCO3- permeability, and may play a role in CSF secretion. One conductance exhibits inward-rectification and is regulated by cyclic AMP. The other is carried by an outward-rectifying channel, which is activated by increases in cell volume. The molecular identity of the anion channels is not known, nor is it clear whether they are expressed in the apical or basolateral membrane. Recent molecular evidence indicates that choroid plexus also expresses the non-selective cation channels such as transient receptor potential channels (TRPV4 and TRPM3) and purinoceptor type 2 (P2X) receptor operated channels. In conclusion, good progress has been made in identifying the channels expressed in the choroid plexus, but determining the precise roles of these channels in CSF secretion remains a challenge for the future.It is now more than 25 years since the publication of the seminal paper which first described the patch clamp method for studying ion channels [1]. In recognition for their work in developing the patch clamp method Bert Sackmann and Erwin Neher, two of the authors on this original paper, were awarded the 1991 Nobel Prize for Medicine. The impact of the method is perhaps most obvious in studies of the activity of individual ion channels (single channel recording). This configuration of the method gives scientists the unique opportunity to study the activity of a single protein. Used in conjunction with recombinant DNA techniques, this method has vastly increased our understanding of how pro