This thesis addresses the regulation of TRPM7 channels by receptor-mediated signals and the effects of the ensuing ionic signals on the cytoskeleton. Several signaling pathways were investigated... Show moreThis thesis addresses the regulation of TRPM7 channels by receptor-mediated signals and the effects of the ensuing ionic signals on the cytoskeleton. Several signaling pathways were investigated that activate TRPM7 channel opening. Stimulation of PLC-activating receptors opens TRPM7 channels, leading to influx of extracellular Ca2+. The results contrast markedly with a report by Runnels et al. who showed inhibition of TRPM7, rather than activation by PLC. To explain this discrepancy, we explored the differences in PIP2-mediated regulation of TRPM7 measured in perforated-patch and whole-cell configuration after intracellular Mg2+ depletion. This leads us to propose that the effects of PLC activation on TRPM7 currents as detected in whole cells can best be viewed as ‘accelerated rundown’ rather than as bona fide signal transduction. Agonist-induced TRPM7 activation and subsequent Ca2+ influx affects the cytoskeleton by phosphorylation of the myosin II heavy chain to promote cytoskeletal relaxation and the conversion of focal adhesions to podosomes. Ca2+ influx appears crucial for the in vivo function of the TRPM7-kinase by triggering the association between the kinase and its substrate. A second effect of receptor-mediated Ca2+ influx can affect the cytoskeleton by translocating Rac in a PKC-dependent manner to the plasma-membrane, where it induces extensive membrane ruffling. Show less
