Dr Louise Robson: Research
Research in the laboratory is focused on understanding the mechanisms underlying the transport of ions and solutes across the renal tubule and the physiological process regulating such transport. While a number of ion channel types are currently under investigation, we are particularly interested in identifying renal K+ channels at a molecular level and determining the physiological role these K+ channels play in renal function.
Techniques in use in the laboratory include whole cell and single channel patch clamp, PCR, immunocytochemistry, Ca2+ imaging, optical cell and tubule diameter measurements and whole kidney in vivo approaches. The specific projects currently under investigation are:
1) The role of KCNE1 in renal function
KCNE1 is a small protein that plays an important physiological role as a K+ channel regulator. In the heart it regulates the K+ channel that is important in cardiac repolarisation, KCNQ1. Mutations in KCNE1 lead to one form of long QT syndrome, which is associated with sudden death due to cardiac failure. KCNE1 also regulates KCNQ1 in the inner ear, and mutations in either of these proteins leads to deafness.
Both these proteins are found in the renal proximal tubule. Here KCNE1 plays a role in maintaining Na+ coupled reabsorption of sugars and amino acids.
Our work has also demonstrated that KCNE1 is important in the process of cell volume regulation. However, it is not clear whether KCNQ1 is the K+ channel regulated by KCNE1 in this nephron segment and research in the laboratory is concentrating on identifying the proximal tubule K+ channel regulated by KCNE1.
2) Polycystic kidney disease – another channelopathy?
Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common inherited renal diseases. It is associated with the progressive development of renal tubular cysts, which replace normal renal tissue. Over time this leads to renal failure in about 50% of sufferers, with these patients requiring dialysis for long-term survival. Studies into the genetic basis of ADPKD have identified two genes that show mutations in ADPKD patients, PKD1 and PKD 2. PKD 1 and PKD 2 encode for two different proteins, polycystin-1 and polycystin-2.
However, although these proteins were identified a number of years ago their functional role in renal tubule cells and why mutations in them cause ADPKD are still not well understood. Expression of both polycystin-1 and polycystin-2 alter Ca2+ permeability, suggesting that they may play a role in the regulation of Ca2+ permeability in vivo, with changes in intracellular Ca2+ subsequently regulating gene transcription and ultimately cell adhesion, cytoskeletal arrangement and cell to matrix interactions, all of which are altered in ADPKD.
Current research in the laboratory is examining how these proteins regulate Ca2+ permeability in a renal cell line. (This work is in collaboration with ACM Ong, Sheffield Kidney Institute, Northern General Hospital).
3) Ca2+-activation K+ channels and collecting duct function
Ca2+-activated K+ channels are a class of K+ channels that are sensitive to the intracellular concentration of Ca2+, with increases in Ca2+ increasing channel activity. They play functional roles in a diverse range of tissues, including setting the membrane potential and also mediating cell volume regulation.
At a molecular level there are three families of Ca2+-activated K+ channels, based on their single channel conductance. These are the high conductance channels (BK), intermediate conductance channels (IK) and small conductance channels (SK). Functional studies have demonstrated Ca2+-activated K+ channels in the renal collecting duct, however the molecular identity and physiological function of these channels is still unclear and this is the focus of the project.
4) P2X receptors in the renal proximal tubule
The renal proximal tubule has the ability to maintain a constant cell volume. In response to cell swelling this is achieved by the activation of efflux pathways for Cl- and K+, the efflux of these ions from the cell followed by water and subsequent cell volume recovery.
Volume regulation is also dependent on the influx of extracellular Ca2+ . P2X receptors are ATP-activated cation channels that may provide such a Ca2+ influx pathway during volume regulation.
This project is investigating the functional expression of these receptors in single proximal tubule cells. Patch clamp techniques have revealed that the cells possess an ATP-activated cation conductance that is inhibited by the P2X antagonists suramin and PPADS.
In addition, both suramin and PPADS inhibit volume regulation in the cells, suggesting that activation of the P2X receptor plays an important role in volume regulation in the renal proximal tubule.