Comparative Study of TRPM5 in Pancreatic ß-Cells of Wistar Kyoto and Goto Kakizaki Rats

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Monteilh-Zoller, Mahealani
thesis / dissertation description
TRPM5 is a member of the melastatin subfamily of the Transient-Receptor-Potential superfamily of ion channels. Through functional analysis of the chromosomal region 11p15.5, TRPM5 was identified and linked to a variety of childhood and adult tumors as well as to Beckwith-Wiedemann syndrome (Prawitt et al., 2000). TRPM5 RNA has been detected in a variety of tissues including: taste receptor cells, small intestines, liver, lungs, testis and brain (Hofmann et al., 2003). In addition, the rat insulinoma (INS- 1) pancreatic ß-cell line was shown to endogenously express TRPM5 (Prawitt et al., 2003). While earlier studies of TRPM5 conducted in taste receptor cells report TRPM5 as a divalent cation channel that is activated through a G protein-coupled receptor/phospholipase C signaling pathway (Perez et al., 2002; Zhang et al., 2003), other studies (Hofmann et al., 2003; Liu and Liman, 2003) have characterized TRPM5 as a Ca2+-activated non-selective monovalent cation channel. I here, hypothesize that the pancreatic ß-cells of Goto Kakizaki will exhibit a reduction in TRPM5 which may contribute to the dysfunction of the ß-cell. To this end, we utilized immunostaining to compare the endogenous expression of TRPM5 in the Wistar Kyoto and Goto Kakizaki (spontaneous non-obese type 2 diabetes model) rat pancreatic ß-cell. We also incorporated the whole-cell patch technique to examine the activation characteristics of TRPM5 in both populations of rat ß-cells. Being that TRPM5 is Ca2+-activated, we included fura-2 Ca2+ measurements to connect intracellular Ca2+- signaling to TRPM5 activation. In addition, we utilized the perforated patch technique to study glucose-stimulated Ca2+-signaling and TRPM5 activation. Our results show TRPM5 expression in Wistar Kyoto rat pancreatic ß-cells with expression in the Goto Kakizaki rat being significantly reduced. We also observe significant differences in the glucose-induced Ca2+-signaling in the Goto Kakizaki rat. Our results suggest that chronic hyperglycemia in the Goto Kakizaki rat reduces expression of TRPM5 and leads to pancreatic ß-cell dysfunction thereby contributing to the progression of type 2 diabetes.