Calcium signalling, divalent cation transport and stimulus-response coupling in mammalian cells
All mammalian cells receive information in the form of extracellular chemical signals - hormones and transmitters. These `instructions' must then be signalled to the cellular machinery to produce a response - the opening of ion channels, the secretion from the cell of a hormone, transmitter or enzyme, the activation of ion pumps or carriers. We are investigating this stimulus-response coupling in a range of cell types. In particular, we study the changes in intracellular free calcium concentration ([Ca2+]i) which are a primary intracellular signal in tissues as diverse as cardiac muscle and epithelial cells. We are also interested in other intracellular signalling molecules, such as diacylglycerols and reactive oxygen species, and and have a special interest in the actions of metal ions (such as iron and heavy metals) in biological systems. Major current areas of investigation in this laboratory are:-
Calcium sensing and transport in epithelia
Apart from being a key intracellular regulator, calcium can also be an extracellular signal, acting on cell surface cation-sensing receptors. In epithelia, a further level of complexity is that calcium transport into and out of cells is organised and regulated to produce, in effect, transfer of calcium ions from one side of the epithelium to the other. We have worked extensively on Ca signalling in a number of such epithelia, including pancreatic acinar (digestive enzyme-secreting) cells, pancreatic ductal (HCO3--secreting) epithelia cells (with Dr Martin Steward), and human placental epithelium (with Professor Colin Sibley and Dr Sue Greenwood in the Faculty of Health Sciences). We are particularly interested in Ca sensing and the control of Ca influx at the luminal side of epithelia. In pancreatic ducts, this may form part of a mechanism of Ca sensing that helps prevent the formation of pancreatic stones.
In human placenta, luminal Ca entry is particularly important as it is the first step in the movment of Ca ions from the mother to the growing baby. We are trying to identify the calcium channels that mediate this Ca entry, and work out how they are controlled. The placenta, uniquely among the bodys organs, has no nerve supply of its own, and the question of what hormones regulate Ca channels and Ca signalling in this tissue (in the absence of neurotransmitters) is particularly interesting.
We are pursuing these investigations using a range of techniques, particularly microscope-based Ca imaging, but also standard molecular methods (RT-PCR, western blotting) and immunocytochemistry
Alteration of calcium signalling by pathological processes
Agents or treatments which interfere with Ca signalling profoundly alter cell function, are implicated in many diseases. We are particularly interested in reactive oxygen intermediates, which are probably important in the pathogenesis of pancreatitis, a serious and sometimes fatal inflammatory disease of the exocrine pancreas. Together with Dr Jason Bruce we are currently measuring oxidative stress in single living cells using fluorescent dyes, and trying to use this to learn how cells "defend" themselves from oxidative damage.
Heavy metals - iron and cardiac myocytes
Heavy metals, most commonly transition metal cations, are typically toxic in biological systems, although some, such as iron and zinc, are necessary for normal cell function and are only toxic in excess. Heavy metal cations are interrelated with Ca signalling as the ions often mimic Ca, being transported by Ca channels and other Ca transport proteins.
We are currently looking at iron transport and the effects of iron in heart muscle cells. Iron-mediated damage to the heart is a major cause of death in patients with Beta-thalassaemia, who become overloaded with iron through the repeated blood transfusions that they need to survive. In collaboration with Dr Mary Diaz of the University of Edinburgh we are trying to work out both how iron enters heart muscle, and how it causes cell damage and death. This work uses fluorescence microscopy to measure Ca transients and contractions in single cardiac cells, and RT-PCR and immunocytochemistry to identify iron transporters.