In our last meeting we introduced one of the major cellular signal tranduction pathways. We saw how a hormone signal could be transduced into increased intracellular cAMP concentrations, which in turn activates enzymes involved in some cellular responses to the hormone. The main idea is recognizing that a signal, rather than a hormone per se , leads to a cellular response. Changing concentrations of cAMP are translated into changes in enzyme activities, and the enzyme activities produce the cellular response.
Most cells express multiple signal transduction pathways.
The cellular actions of these two intracellular signals are fairly similar. Both messengers act by binding to specific proteins, and the binding activates the proteins by causing them to undergo conformational changes. Very often, multiple intracellular messengers interact with each other, and the cross-talk among signal transduction pathways influences the intensity of a cellular response to hormones or other extracellular signals. For an example, a diuretic hormone known as AVP increases fluid secretion in mammalian kidneys. At the same time, certain prostaglandins attenuate the intensity of fluid secretion.