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Activation of beta-adrenergic receptors leads to relaxation of smooth muscle in the lung, and dilation and opening of the airways.
Beta-adrenergic receptors are coupled to a stimulatory G protein ofadenylyl cyclase. This enzyme produces the second messenger cyclic adenosine monophosphate (cAMP). In the lung, cAMP decreases calcium concentrations within cells and activates protein kinase A. Both of these changes inactivate myosin light chain kinase and activate myosin light chain phosphatase. In addition, beta-2 agonists open large conductance calcium-activated potassium channels and thereby tend to hyperpolarize airway smooth muscle cells. The combination of decreased intracellular calcium, increased membrane potassium conductance, and decreased myosin light chain kinase activity leads to smooth muscle relaxation and bronchodilation.
Myosin light-chain kinasealso known asMYLKorMLCKis aserine/threonine-specific protein kinasethatphosphorylatesthe regulatory light chain ofmyosin II.[3] Theseenzymesare important in the mechanism of contraction inmuscle. Once there is an influx ofcalciumcations (Ca2+) into the muscle, either from thesarcoplasmic reticulumor from theextracellular space, contraction of smooth muscle fibres may begin. First, the calcium will bind tocalmodulin. This binding will activate MLCK, which will go on to phosphorylate themyosin light chainatserineresidue 19. This will enable the myosincrossbridgeto bind to theactin filamentand allow contraction to begin (through thecrossbridge cycle). Since smooth muscle does not contain atroponincomplex, asstriated muscledoes, this mechanism is the main pathway for regulating smooth muscle contraction. Reducing intracellular calcium concentration inactivates MLCK but does not stop smooth muscle contraction since the myosin light chain has been physically modified through phosphorylation. To stop smooth muscle contraction this change needs to be reversed. Dephosphorylation of the myosin light chain (and subsequent termination of muscle contraction) occurs through activity of a second enzyme known asmyosin light-chain phosphatase(MLCP).
Incell biology,Protein kinase A(PKA) is a family ofenzymeswhose activity is dependent on cellular levels ofcyclic AMP(cAMP). PKA is also known ascAMP-dependent protein kinase(EC2.7.11.11). Protein kinase A has several functions in the cell, including regulation ofglycogen,sugar, andlipidmetabolism.
It should not be confused withAMP-activated protein kinase- which, although being of similar nature, may have opposite effects -[1]nor be confused withcyclin-dependent kinases(Cdks), nor be confused with theacid dissociation constantpKa.
In the field ofmolecular biology, thecAMP-dependent pathway, also known as theadenylyl cyclasepathway, is aG protein-coupled receptor-triggeredsignaling cascadeused incell communication.[1]
G protein-coupled receptors(GPCRs) are a large family ofintegral membrane proteinsthat respond to a variety of extracellular stimuli. Each GPCR binds to and is activated by a specificligandstimulus that ranges in size from small moleculecatecholamines, lipids, orneurotransmittersto large protein hormones. When a GPCR is activated by its extracellular ligand, a conformational change is induced in the receptor that is transmitted to an attached intracellularheterotrimeric G proteincomplex. TheGsalpha subunitof the stimulated G protein complex exchangesGDPforGTPand is released from the complex.
In a cAMP-dependent pathway, the activated Gsalpha subunit binds to and activates an enzyme calledadenylyl cyclase, which, in turn, catalyzes the conversion ofATPintocyclic adenosine monophosphate(cAMP).[2]Increases in concentration of thesecond messengercAMP may lead to the activation of
cyclic nucleotide-gated ion channels[3]
exchange proteins activated by cAMP (EPAC)[4]such asRAPGEF3
popeye domain containing proteins (Popdc)[5]
an enzyme calledprotein kinase A(PKA).[6]
The PKA enzyme is also known as cAMP-dependent enzyme because it gets activated only if cAMP is present. Once PKA is activated, it phosphorylates a number of other proteins including:[7]
enzymes that convertglycogenintoglucose
enzymes that promote muscle contraction in the heart leading to an increase in heart rate
transcription factors, which regulate gene expression
Specificity of signaling between a GPCR and its ultimate molecular target through a cAMP-dependent pathway may be achieved through formation of a multiprotein complex that includes the GPCR, adenylyl cyclase, and the effector protein
Aetiology
the cause, set of causes, or manner of causation of a disease or condition:
Asthma is an —— ——– disease
obstructive airway
In asthma the spirometry will show:
1 = Increased FVC > 70%
2 = Reduced FVC < 70%
3 = Increased FEV1 > 70%
4 = FEV1/FVC of > 70%
5 = FEV1/FVC of < 70% i
5
Its obstructive and hence FEV will reduce
Obstructive Airway Disease
Obstructive Airways Disease Spirometry
↓ FEV1
↔ FVC (unchanged)
↓ FEV1/FVC < 70%
FEV1 = forced expiratory volume in 1 second
FVC = forced vital capacity
Asthma definition
Asthma is characterised by (2):
obstructive airways disease
Diagnosis of asthma
Epidemiology of asthma:
Aetiology of Asthma
The genetic predisposition is actually disposition to atopy; hence will always ask patient about hayfever, eczema and family history of asthma
Genetics of asthma
Atopy
pathophysiology of asthma: airway inflammation:
Pathophysiology of asthma: two phase response:
Pathophysiology of asthma: IgE antibodies bind to receptors on mast cells and eosinophils and stimulate them to release:
What are targets for therapies for asthma?
Mediators: histamines prostaglandins, cysteinyl leukotrienes
What distinguishes asthma from COPD?
Reversibility of bronchoconstriction
Pathophysiology of asthma: Late phase response:
Pathophysiology of asthma: dynamic hyperinflation:
What type of immune cells are associated with acute asthma?
Eosinophils
What are neutrophils associated with (asthma)?
Pathophysiology of asthma