Modulation of G-protein activated, inwardly rectifying K+ -channels by second messenger cascades

G-protein activated, inwardly rectifying K+-channels fulfil important physiological functions like vagal regulation of the heartbeat and central pain perception. Many aspects of their function and the mechanisms of these functions are, however, still poorly understood. The goals of the current proposal are to investigate and to understand the regulation of GIRK`s by second messenger cascades, like cAMP induced protein phosphorylation. This modulation will be investigated at the molecular level, i.e. we want to understand which subunit is responsible and whether GIRK proteins themselves represent the molecular targets for protein phosphorlylation or whether the effect is mediated via advisory proteins. The structural determinant responsible for the modulation of ion channel activity will be deciphered. Within the projected time span of three years we hope to be able to come out with a complete picture about the mechansims and molecular events that take place during this special form of regulation of protein function by protein phosphorylation. Modulation of membrane-delimited gated K+ channels by cytosolic second messenger pathways is likely to entail important physiological consequences, but also bears the potential for use in pharmaceutical therapy of diseases related to this important group of ionchannels. Hence we expect from the current proposal major insight into molecular mechanisms of signal transduction and cell biology.

Signal transduction and cellular communication within and in-between living cells is pivotal for the concerted action of the cellular units composing multicellular organisms including man. C-protein activated, inwardly rectifying K-channels (GIRKs) are central players in the transduction of neurotransmitter and hormone action in order to steer single cell metabolism and reactions. Best understood are their roles in the regulation of the heartbeat by the autonomous nervous system and in central pain perception. Many other vital functions exist. Within the course of project P13724 it was elucidated that GIRKs not only transduce neurotransmitter and hormone action to changes in cellular resting potential via C-protein activation, but GIRK activity by itself is tuned by second messenger cascades within cells, like cAMP dependent protein phosphorylation. Moreover other regulatory pathways, like free oxygen radical production and therapeutical drugs, were also identified. A "molecular switch" for C-protein activation was discovered and recognized as three adjacent amino acids within the G ß/ binding region, that become reversibly phoshorylated by cAMP dependent protein kinase. These discoveries are not only a significant contribution to the cell biology of signal transduction, but also bear the potential to novel therapeutical interventions.