Stimulus-response coupling, role

Cellular Calcium Regulation Calciiun plays critical roles in cellular communication and regulation. The normally very low resting free ionized concentration of Ca is maintained by a variety of ion channels, pumps, and intracellular storage processes. The elevation of intracellular Ca levels during cell stimulation serves to couple information with cellular response -stimulus-response coupling. The control of Ca " homeostasis represents, therefore, a potentially powerful control of cellular excitability and response [ 5 ]. 

Stimulus Response Coupling, the Role of Intracellular Calcium-binding Proteins, V. L. Smith, J. R. Dedman, eds. CRC Press, Boca Raton, FL 1990. 

Histamine released from mast cells plays an important physiological role in immediate hypersensitivity and allergic responses. In addition, histamine functions as a neurotransmitter in the CNS and it is a potent stimulus for gastric acid secretion. These actions depend on the interaction of histamine with two types of receptors, Hi and H2. Hi and H2 receptors are coupled via G proteins to phospholipase C and adenylyl cyclase, respectively. The principal H3 receptor response is stimulation of gastric acid secretion, whereas other actions of histamine (e.g., smooth muscle contraction, vasodilation, increased capillary permeability, pain, and itching) are prunarily mediated by Hi receptors. 

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