- Professor, Department of Medicine - Section of Endocrinology, Department of Pediatrics - Section of Endocrinology, Committee on Cell Physiology, Committee on Molecular Medicine/MPMM, Committee on Molecular Metabolism and Nutrition, Committee of Clinical & Translational Science
- Director, Kovler Diabetes Center
M.D., The University of Chicago, 1986
Ph.D., The University of Chicago, 1982
A.B., Harvard College, 1976
The University of Chicago
900 E 57th Street
Chicago, Illinis 60637
Phone: (773) 702-9180
Lab: (773) 702-2563
Molecular and Biophysical Aspects of Insulin Secretion; Ion Channels Related to Beta Cell Function; Functional Imaging of Islet Physiology and Exocytosis
Studies on Ion Channels of Insulin Secreting Cells
Our goal is to develop a greater understanding of the relationship of ion channels, regulation of intracellular Ca2+ concentration, and insulin secretion in normal pancreatic ß-cells and how this process may be dysfunctional in diabetes mellitus. The work described here is among the first series of investigations to examine the expression of K+ and Na+ ion channel genes in islet cells. We have also cloned and characterized a new Ca2+ channel alpha1 subunit, which is expressed in both brain and neuroendocrine cells.
Recently we reported the identification of cDNAs encoding delayed rectifier-type K+ channels in human insulin-secreting cells. In addition several other related K+ channel cDNAs were isolated from human genomic and skeletal muscle libraries, some of which have also been shown to be present in normal islets. In collaboration with Dr. D. J. Nelson, our expression studies in Xenopus oocytes and stable cell lines have confirmed the similarity of these currents to those observed in normal cells. We have also shown that these cDNAs encode subunits that can arrange to form active heteromultimers, which also may be an important mechanism in generating the K+ currents present in a variety of tissues, such as brain, heart, and pituitary. Antibodies directed against the channel and a fusion epitope have allowed characterization of the protein in transfected cell lines and transgenic animals. Additional studies have examined the mechanisms of subunit association and inactivation. The expression of one of the human K+ in pancreatic ß-cells of transgenic mice is associated with hyperglycemia, as anticipated. This may provide a model in which to study the role of membrane potential in glucose-induced insulin signalling. Ongoing studies include generation of K+ channel knock-out mice by a dominant-negative approach, examination of the effects of the -subunit, and expression via adenovirus vectors.
Several members of the inward rectifier class have been cloned and expressed. In collaborative studies, we have identified several new cDNAs and their genes encoding new members of this family in insulin secreting cells, including the human ROMK1 ATP-regulated inward rectifier, and GIRK1, a G-protein-linked inward rectifier. An epitope tag has been added to the GIRK1 cDNA, enabling us to study the expression of the protein as we examine its co-expression with G-protein coupled receptors.
Other studies are in progress to examine the role of Na+ and Ca2+ channels in insulin secretion. These studies have shown that a different subset of voltage-dependent Na+ channel gene isoforms (of which five are known) are expressed in islets that are in the adult brain. In a joint project with Prof. R. J. Miller we have cloned and studied the expression of a new Ca2+ channel alpha one subunit alpha 1E. This channel is expressed strongly in multiple nuclei of the brain, in pancreatic ß-cells and neuroendocrine cell lines, and has several splice variants. The intact cDNA is now being examined in several expression systems.