Trigger signal

FIGURE 10.31 The umbrella model of membrane chamiel protein insertion. Hydrophobic helices insert directly into the core of the membrane, with amphipathic helices arrayed on the surface like an open umbrella. A trigger signal (low pH or a voltage gradient) draws some of the amphipathic helices into and across the membrane, causing the pore to open. 

FIGURE 17.24 Ca is the trigger signal for muscle contraction. Release of Ca" through voltage- or Ca" -sensitive channels activates contraction. Ca" pumps induce relaxation by reducing the concentration of Ca" available to the muscle fibers. 

Activated Ras triggers signalling down the Raf-MEKl / 2-Erkl/2-RSKl MAP kinase cascade. This process is inhibited by the RasGAP neurofibromin (NF1). Both Erkl/and RSK1 can directly phosphorylate TSC2 and these phosphorylation events inhibit the GAP activity of TSC2 and thus ultimately promote mTORCl activity. 

If there is too much damage such that the level of ATP is insufficient and/or the machinery of apoptosis is damaged, then necrosis will ensue. Also the exact pathway may depend on the cell type and the particular trigger signal. 

Zaidi M, Shankar VS, Towhidul Alam AS, Moonga BS, Pazianas M, Huang CL. 1992b. Evidence that a ryanodine receptor triggers signal transduction in the osteoclast. Biochem Biophys Res Commun. 188 1332-6. 

Open-looped systems operate on trigger signals sent from an external device that thereby activates the implanted system and causes drug release within the body. Pulse delivery occurs by magnetic, ultrasonic, or electronic means in open-looped systems. 

Fig. 8.22. A diagram of some of the events associated with apoptosis, showing related flow cytometric assays (outlined in bold boxes). Although it is generally agreed that calcium flux and caspase activation are early events following the trigger signal, the events following on from there may be essential steps in an ordered pathway or may be independent and merely symptomatic of apoptosis.

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