of Cell Physiology
Tel: +44 (0)1223 333822, Fax: +44 (0)1223 333840, E-mail: email@example.com
Chris Huang (left), Richard Balasubramaniam (right)
Photo: Roger Thomas
Qualifications: BA BM BCh MA DM DSc (Oxon), MA PhD MD ScD (Cantab)
Chris Huang held an open Florence Heale Scholarship whilst reading The Honour School of Physiological Sciences at The Queen's College, Oxford before proceeding to Clinical Studies at Oxford University Clinical School, and completing preregistration appointments with Profs Sir David Weatherall and John Ledingham in the Nuffield Department of Medicine. After completing a PhD at the Physiological Laboratory and Gonville and Caius College, as an MRC Scholar under Prof R H Adrian’s supervision, he became Assistant Lecturer and Lecturer in Physiology, then Reader in Cellular Physiology at Cambridge, whilst holding a Fellowship and directing Medical Studies at New Hall for much of this time.
His research has primarily concerned the mechanisms through which physiological activation takes place at the membrane level and its cellular and tissue propagation, using biophysical, microscopic and imaging methods. These were applied to early events in the activation of muscle and the maintenance of its tubular system, osteoclast regulation, and to the MRI analysis of physiological events in the central nervous system and heart, for which he was awarded, successively, the degrees of DM and DSc of the University of Oxford.
Chris Huang is a recipient of the LEPRA Award (British Leprosy Relief Association), and the Benefactor's Prize (The Queen's College, Oxford), Brian Johnson in Pathology (Oxford University Clinical School), and the Rolleston Memorial Prize (University of Oxford) and Gedge Prize (University of Cambridge) for Physiological Research. He has been an editor and distributing editor for the Journal of Physiology, chaired the editorial board for the Monographs of the Physiological Society, and currently is Biological Secretary of the Cambridge Philosophical Society for which he chairs the Editorial Board of Biological Reviews. He has been ProCultura Foundation Visiting Professor in Physiology for the University of Debrecen, Hungary, and is currently a Visiting Professor to Mount Sinai Medical School, New York. He plays the violin with the Cambridge String Players and reads Shakespeare in his spare time.
My principal research output has concerned the mechanisms through which physiological activation takes place at the membrane level and its cellular and tissue propagation. This has required biophysical, microscopy and imaging methods drawn from several biological disciplines each chosen to deal with the experimental systems at hand.
Cellular triggering involving the intracellular ryanodine receptor (RyR) in excitable cells
My contributions on muscle activation demonstrated that release of intracellularly stored Ca2+ into the cytosol is triggered by conformational changes in regulatory intramembrane macromolecules following voltage change. My work first established (1) the recently discovered small intramembrane electric currents or charge movements as the electrical signature for such conformational changes. This led to (2) pharmacological resolution of their contributing components each representing individual intramolecular species. This used Fourier Transform analyses of the charging signals followed by their first pharmacological characterization. A novel kinetic superposition analyses then demonstrated that (3) each component constituted an independent membrane transition, rather than forming part of a single reaction sequence, localized to functionally distinct different membrane regions of the contractile cell.
(4) A specific, charging component was then identified with the triggering of contractile activation on the basis of its steep voltage dependence, anatomical localization and its pharmacological and kinetic parallels with measured intracellular calcium signals. Statistical mechanical investigation of (5) the conformational mechanisms for such charge transfers indicated a steeply voltage-dependent intramembrane molecular process, for which dielectric spectroscopic analysis implicated cooperative regulatory mechanisms as opposed to relaxations in simple linear processes.
(6) The specific molecules involved were next identified: use of dihydropyridine calcium antagonists and calcium withdrawals identified the charging element with a modified calcium channel. Yet RyR-specific agents altered its kinetic but spared its steady state properties. These observations prompted experiments that strongly supported the existence of (7) direct allosteric interactions between tetradic groups of dihydropyridine receptors located within the cell surface membrane and RyR-Ca2+ release channels gating calcium release from intracellular stores. My most recent experiments suggest that (8) depolarization drives a configurational change that dissociates this allosteric coupling and thereby frees the RyR to release stored Ca2+, a situation that can take place even in fully polarized and therefore otherwise quiescent fibres as exemplified in the illustration below, which illustrates Ca2+ waves represented by false colour maps on an xt plot generated by fluo-3 fluorescence resulting from ryanodine receptor dissociation from its controlling dihydropyridine receptor-voltage sensor in the tubular membrane of skeletal muscle: front cover in the Journal of Physiology.
Membrane structures required for the cellular activation process
The above excitation-contraction coupling mechanisms together with their (1) associated tubular membrane structures develop coincidentally with the completed sarcomeres in Xenopus embryos. The latter provide an anatomical framework for this early embryological establishment of an adult triggering pattern independent of extracellular calcium entry. This is lost in pathological conditions such as muscular dystrophy, muscle fatigue, and osmotic manipulations that cause tubular disruption and vacuolation, that can be followed by confocal microscopy methods as exemplified for an intact fibre (left) and a vacuolated fibre (right) exemplified below. The preservation of tubular system integrity was investigated using electrophysiological and two-photon confocal microscopic methods. These developed (2) a reliable experimental procedure of initiating vacuolation. Vacuolation was characterized into (3) initial reversible stages and final irreversible tubular detachment and (4) an underlying osmotic mechanism for this process was explored. This led to a (5) specific model for the maintainence of transverse tubular integrity in which cellular water entry through a surface membrane Na-K-2Cl exchanger balanced water extrusion by Na-K-ATPase into the tubules. The latter would generate an intraluminal hydrostatic pressure that would normally preserve their patency, but which would cause tubular distension and vacuolation with the excessive transport activity that might follow an osmotic stress.
Parallel mechanisms in nonexcitable cells also involving surface RyRs
A similar biophysical approach applied to single isolated osteoclasts, cells central to the pathogenesis of osteoporosis, successfully demonstrated, then characterized, parallel membrane controls of intracellular calcium redistribution in nonexcitable cells. These studies began by demonstrating that (1) osteoclasts operate at least two signaling pathways that involve different G-proteins and elevate either cytosolic [Ca2+] or [cAMP], whose (2) activation produces cell retraction or a quiescence of cell motility respectively.
These findings led to demonstration of a local mechanism for control of the osteoclastic bone resorption cycle as shown in the sketch below. (3) an increased ambient calcium as might result from local hydroxyapatite dissolution elevated both cytosolic [Ca2+] and inhibited bone resorption. Microspectrofluorimetric studies of cellular responses to agonist applications then implicated (4) a novel, surface membrane 'calcium receptor' in this local functional regulation whose occupancy drove the calcium redistribution from intracellular stores and triggered a capacitative entry of external calcium. The latter reduced cell motility, adhesion upon substrate and therefore bone resorptive activity.
Confocal microscope studies that used specific fluorescent-labeled antibodies raised in muscle then demonstrated that (4) this local regulation of osteoclast activity involves a unique cell surface cardiac-muscle-type ryanodine receptor (RyR). This thus demonstrated both surface membrane RyRs and their involvement in osteoclast function for the first time. We then went on to demonstrate (5) similar operations of Ca2+ receptors in other cell systems, and have demonstrated (6) regulation of such osteoclast RyRs by caffeine, ryanodine itself, ruthenium red as well as cyclic ADP-ribose. (7) The most recent experiments have broadened the investigation of the role of RyRs in coupling signalling to metabolism in bone resorbing osteoclasts.
Tissue spread of cellular activation: Biophysical methods applied to integrative physiology
The studies of activation at the cellular level using electrophysiological, microspectrofluometric and imaging methods has led to their extension to more extensive physiological systems at the integrationist level using magnetic resonance imaging (MRI) methods. MRI is becoming increasingly promising as an investigative tool that will enable non-invasive studies of physiological processes at the whole organism level. Their development en passant led to (1) the first MRI demonstration of chronic cardiac muscle changes in vivo following spontaneous hypertension and experimental diabetes, but the primary objective was the development of (2) MRI methods to map strategic cerebral diffusion-related parameters to high resolution. The work dealt successfully with the theoretical, methodological and practical problems associated with development of robust optimized protocols for diffusion tensor measurements using as subject healthy human brain. This gave systematic high-resolution maps of the principal diffusivities and the associated rotationally invariant isotropy and anisotropy indices and a platform by which we could detect and analyze physiological abnormalities by such diffusion-weighted imaging (DWI).
Having done this, it was possible to achieve (3) the first successful physiological demonstration and quantitative analysis of cortical spreading depression (CSD) evoked with KCl in the gyrencephalic brain, using time-lapse, diffusion-weighted MRI. CSD has been implicated in human migraine with aura and leads to a transient reduction in cerebral water diffusibility, which, hitherto, has been detected with DWI only in rodent brain. The subsequent statistical signal analysis successfully determined regions of significant change in the ADC maps both through time, within a given pixel, and in comparisons between pixels. This made it possible to (4) characterize the spatial and temporal spread of the advancing ADC waves over the brain surface. This demonstrated a clear-cut decrease in the cerebral apparent diffusion coefficient (ADC) in selected pixels and permitted their spatial and temporal characterization as exemplified in the MRI image shown below. The most recent developments have extended these methods to successfully demonstrate (5) effects of the possible antimigraine agent, tonabersat upon CSD and of (6) hypercapnia, the antipsychotic agents sulpiride and mCPP, and (7) the Ca2+ antagonist MK-801 upon vascular changes in a similar mammalian brain preparation. This has attracted a major collaboration with GlaxoSmithKline on the (8) application of these findings to pathophysiological changes following stroke and head injury.
Dr Richard Balasubramaniam [BHF Training Fellow]
Dr James Fraser [George Henry Lewes Studentship]
Ms Bina Mistry – Research Worker [MRC: in collaboration with Dr. Andrew Grace and Richard Saumarez]
Dr Justin Smith [GlaxoSmithKline postdoctoral fellow]
Kate Stokoe [BHF studentship]
Juliet Usher-Smith [MB-PhD programme]
Dr Glynn Thomas [BHF Senior Clinical Fellow]
Recent PhD students
Justin Smith – Faculty studentship
Bhashkar Mukherjee – MB PhD student [MRC]
Daniel Bradley – BBSRC Committee Studentship
Yu Lu – Research Student – Cambridge Overseas Trust Studentship
Dr Sangeeta Chawla [BBSRC David Philips Fellow]
Prof Mone Zaidi, Mt Sinai Medical School, NY, USA
Dr Jamie Vandenberg, University of New South Wales, Australia
Dr Andrew Grace, Dept of Biochemistry and Papworth Hospital
Dr Lauren MacKenzie [Gonville & Caius RF and The Babraham Institute]
Dr Richard Saumarez, Dept of Engineering and Papworth Hospital
Dr Jeremy Skepper, Multi-Imaging Centre, University of Cambridge
Prof Laurie Hall, Herchel Smith Laboratory of Medicinal Chemistry, University of Cambridge
Dr Michael James, GlaxoSmithKline, Neurology Centre of Excellence in Drug Discovery
Dr James Fawcett, Brain Repair Centre, University of Cambridge
I am also a member of the following MRC Co-operative Groups
MRC Calcium Homeostasis Co-operative Group: Prof RC Thomas, Dr C Schweining, Dr M Mahaut-Smith, Dr M Mason, Dr P Thorne.
MRC Cardiovascular Biology Co-operative Group: Prof J Metcalfe, Dr A Grace, Dr P Kemp, Dr R Farndale.
I am grateful for support from the Leverhulme Trust, the BBSRC (project grant and studentship), the MRC (Joint Research Equipment Initiative, MRC Co-operative Groups and project grants), the Wellcome Trust, British Heart Foundation, EPSRC (Joint Research Equipment Initiatives), GlaxoSmithKline (UK), the Herchel Smith Endowment and the University of Cambridge.