I am a Neuroscientist and a Professor in the Department of Biochemistry at UCC as well as an active and productive researcher. My research focuses on characterization of potassium channels in glial cells with an emphasis on the functional role of these channels in homeostatic mechanisms. One of my most significant research contributions in this area is related to elucidating the role of glial Kir4.1 potassium channels in potassium and glutamate buffering. I have published more than 50 articles in peer-reviewed journals and have had NIH grant support for my research since 1996. In addition, I have had a long-standing commitment to facilitating the research endeavour at UCC. I am currently one of the PIs of the RCMI program. Prior to taking over this position, I served for 14 years as coordinator of the RCMI funded Common Instrumentation Area and Services Core facility at UCC. This is a facility that houses common use instrumentation and provides services to investigators through an electronics technician and a machinist/handyman. In addition, I was the Director of the RCMI-funded Neuroscience Research Center and am the Associate Scientific Director of the Integrative Center for Glial Research. I am a past president of the Puerto Rico Chapter of the Society for Neuroscience and have organized Conferences and Symposia including the Annual Puerto Rico Neuroscience Conference and the Annual CaribeGlia Minisymposium. These activities were facilitated by my strong collaborations with researchers from the mainland USA and Europe.
Contributions to Science
1) One of my most significant research contributions to date is elucidating the role of glial Kir4.1 potassium channels in astrocytic potassium and glutamate buffering. I have extensive background in functional characterization of potassium channels in glial cells with an emphasis on the role of these channels in homeostatic mechanisms, but these studies were initially hampered by the lack of specific potassium channel blockers. To overcome this problem, we were one of the first groups to use siRNA technology to selectively down-regulate proteins (in this case potassium channels) in astrocytes.
2) Diabetics are at risk for a number of serious health complications including an increased incidence of epilepsy and poorer recovery after ischemic stroke. Astrocytes play a critical role in protecting neurons by maintaining extracellular homeostasis and preventing neurotoxicity through glutamate uptake and potassium buffering. These functions are aided by the presence of potassium channels, such as Kir4.1 inwardly rectifying potassium channels, in the membranes of astrocytic glial cells. Using a variety of techniques including used q-PCR, Western blot, patch-clamp electrophysiology studying voltage and potassium step responses and a colorimetric glutamate clearance assay, we assessed Kir4.1 channel levels and homeostatic functions of rat astrocytes grown in normal and high glucose conditions. We found that hyperglycemia decreases Kir4.1 potassium channel expression and impairs homeostatic functions of astrocytes. Our results suggest that down-regulation of astrocytic Kir4.1 channels by elevated glucose may contribute to the underlying pathophysiology of diabetes-induced CNS disorders and contribute to the poor prognosis after stroke.
3) Inwardly rectifying potassium channel Kir4.1 is critical for glial function, control of neuronal excitability, and systemic K+ homeostasis. Genetic inactivation of these channels in glia impairs extracellular K+ and glutamate clearance and produces a seizure phenotype. In both mice and humans, polymorphisms and mutations in the KCNJ10 gene have been associated with seizure susceptibility. In mice, we demonstrated that there are differences in Kir channel activity and potassium- and glutamate-buffering capabilities between astrocytes from seizure resistant C57BL/6 (B6) and seizure susceptible DBA/2 (D2) mice that are consistent with an altered K+ channel activity as a result of genetic polymorphism of KCNJ10 (gene encoding Kir4.1). In addition, we investigated the functional significance of novel human mutations in Kir4.1 which have been associated with EAST/SeSAME syndrome, characterized by mental retardation, ataxia, seizures, hearing loss, and renal salt waste. All of the mutations compromised channel function, but the underlying mechanisms were different. I served as primary investigator or co-investigator on all of these studies.
4) Kir4.1 potassium channels are expressed in glial cells in the brain and retina and attempts had been made to equate properties of exogenously expressed Kir4.1 currents with those of native K+ currents in glial cells. There were nagging problems however with assigning native currents to Kir4.x channels. One major concern was that in many native tissues, the putatively correlated currents show much weaker rectification than reported for cloned Kir4.1 channels. We found that the rectification in physiological concentrations of potassium was similar to that reported in native tissue. We also found two types of block that help promote potassium uptake by the cells. When [K+]o is rapidly increased, as would occur during neuronal excitation, ‘‘fast block’’ would be relieved, promoting potassium influx to glial cells. Increase in [K+]in would then lead to relief of ‘‘slow block,’’ further promoting K+-influx.
5) Excitotoxicity due to glutamate receptor over-activation is one of the key mediators of neuronal death after an ischemic insult. Therefore, a major function of astrocytes is to maintain low extracellular levels of glutamate. The ability of astrocytic glutamate transporters to regulate the extracellular glutamate concentration depends upon the hyperpolarized membrane potential of astrocytes conferred by the presence of K+ channels in their membranes. We have shown that TREK-2 potassium channels in cultured astrocytes are up-regulated by ischemia and may support glutamate clearance by astrocytes during ischemia. Recently, we determined the mechanism leading to this up-regulation and assessed the localization of TREK-2 channels in astrocytes after transient middle cerebral artery occlusion. We first demonstrated that TREK-2 channels were up-regulated after ischemia via a mechanism which required De novo protein synthesis, but did not require increases in TREK-2 mRNA. Immunohistochemical studies revealed TREK-2 localization in astrocytes together with increased expression of the selective glial marker, glial fibrillary acidic protein, in brain 24 hours after transient middle cerebral occlusion. Our data indicate that functional TREK-2 channels are up-regulated in the astrocytic membrane during ischemia through a mechanism requiring De novo protein synthesis. These study provides important information about the mechanisms underlying TREK-2 regulation, which has profound implications in neurological diseases such as ischemia where astrocytes play an important role.