Intracellular messenger systems

METH-Induced Alterations in Intracellular Messenger Systems Related... 

Upon activation all three (X2AR subtypes are coupled to their intracellular messenger systems via heterotrimeric G /0 proteins (Figure 2). Intracellular consequences of 0C2AR activation are reduced cAMP levels due to inhibition of adenylyl cyclase, opening of GIRK K+ channels, inhibition of neuronal Ca2+ channels, and... 

Neurotransmitters such as glutamate interact with a variety of receptors that are coupled to second messenger systems. The effects of mild hypothermia on ischemia-induced changes in intracellular messenger systems and mediators have also been studied and are described in Chapter 2. 

Fig. 9. The interaction of ACTH with the cyclic AMP and calcium intracellular messenger systems in the regulation of steroidogenesis in the adrenocortical zona glomerulosa cell comparison with angiotensin II and potassium. ACTH activates both adenylate cyclase and calcium influx, here shown as involving two receptor subtypes (R, and R2) although such receptor subtypes have not been identified. The A-kinase and calmodulin systems produce individual responses of characteristic amplitudes and time-courses, which combine to give the observed response of the intact cell. The sequence of events for ACTH is compared to those for the other two major stimuli of steroidogenesis in the zona glomerulosa cell, angiotensin II and potassium. From Ref. 41.

Calcium, via calmodulin, also activates cyclic AMP phosphodiesterases which inactivate cyclic AMP by metabolism to AMP. Inhibition of phosphodiesterase yields a small increase in ACTH-stimulated steroidogenesis [2], This is relatively slight in the adrenocortical zona fasciculata-reticularis cell, which has a low phosphodiesterase level the zona glomerulosa cell has a higher activity [60,61], which may result from higher level of activation of the calcium/calmodulin intracellular messenger system in the zona glomerulosa. 

Phospholipase C/DAG/IP3. The phosphoinositide system is an important intracellular messenger system. Two enzymes families are targets of G-proteins, phosphoinositide-specific phospholipase C (PLC), and phosphoinositide 3-kinase (PI3K). It is well established that receptor-dependent activation of phospholipase C (PLC) results in the... 

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