proteins for different cellular functions in different cell types.
Regulation of transporter activity at the gene level usually occurs within hours and days and is therefore classified as long‐term or chronic regulation. Long‐term regulation usually occurs when the body undergoes massive change, such as during development or the occurrence of disease. Regulation at the posttranslational level usually occurs within minutes or hours and is therefore classified as short‐term or acute regulation. Short‐term regulation usually occurs when the body has to deal with rapidly changing amounts of substances as a consequence of variable intake of drugs, fluids, or meals, as well as metabolic activity.
The overlapping substrate specificities among different transporters or different isoforms of the same transporter, their wide tissue distributions, and the various types of regulation of expression and function, mediated by signaling molecules secreted from remote tissues into the body fluids, contribute to the complicated communication network. Hormones and growth factors produced and released from the original organ under the internal and external stimuli arrive at the target organ and regulate the transporters in the target organ. Such networks contribute to intercellular and inter‐organ communication. This communication between cells, as well as between organs, regulates local and whole‐body homeostasis of endogenous substrates.
1.9 CONCLUSION
As our readers have come to expect, the current and comprehensive information about the drug transporters is the major distinguishing feature of this book. The knowledge presented in this book will enrich our understanding on how pathological conditions, genetic variation, cellular signaling, aging, and drug–drug interactions impact transporter‐mediated drug disposition.
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