Stefan Mergler a , Mathias Z. Strowski a , Simone Kaiser c , Thomas Plath c , Yvonne Giesecke a , Marleen Neumann a , Hiroshi Hosokawa d , Shigeo Kobayashi d , Jan Langrehr b , Peter Neuhaus b , Ursula Plöckinger a , Bertram Wiedenmann a , Carsten Grötzinger a
05 April 2007
TRPM8 is a member of the melastatin-type transient receptor potential ion channel family. Activation by cold or by agonists (menthol, icilin) induces a transient rise in intracellular free calcium concentration ([Ca<sup>2+</sup>]<sub>i</sub>). Our previous study demonstrated that Ca<sup>2+</sup>-permeable cation channels play a role in IGF-1-induced secretion of chromogranin A in human neuroendocrine tumor (NET) cell line BON [Mergler et al.: Neuroendocrinology 2006;82:87–102]. Here, we extend our earlier study by investigating the expression of TRPM8 and characterizing its impact on [Ca<sup>2+</sup>]<sub>i</sub> and the secretion of neurotensin (NT). We identified TRPM8 expression in NET BON cells by RT-PCR, Western blotting and immunofluorescence staining. Icilin increased [Ca<sup>2+</sup>]<sub>i</sub> in TRPM8-transfected human embryonic kidney cells (HEK293) but not in mock-transfected cells. Icilin and menthol induced Ca<sup>2+</sup> transients in BON cells as well as in primary NET cell cultures of two different pancreatic NETs as detected by single cell fluorescence imaging. Icilin increased non-selective cation channel currents in BON cells as detected by patch-clamp recordings. This activation was associated with increased NT secretion. Taken together, this study demonstrates for the first time the expression TRPM8 in NET cells and its role in regulating [Ca<sup>2+</sup>]<sub>i</sub> and NT secretion. The regulation of NT secretion in NETs by TRPM8 may have a potential clinical implication in diagnosis or therapy.