Polarity in intracellular calcium signaling

Article Abstract:

Author's Abstract: COPYRIGHT 1999, John Wiley & Sons, Inc. The concentration of free calcium ions (Ca(super 2+) in the cytosol is precisely regulated and can abe rapidly increased to various types of stimuli. Since CA(super 2+) can be used to control different processes of the same cell, the spatial organization of cytosolic Ca(super 2+) signals is of considerable importance. Polarized cells have advantages for Ca(super 2+) studies since localized signals can be related to particular organelles. The pancreatic acinar cell is well-characterized with a clearly polarized structure and function. Since the discovery of the intracellular Ca(super 2+)-releasing function of inositol 1,4,5-trisphosphate (IP(sub 3)) in the pancreas in the early 1980s, this cell has become a popular study object and is now one of the best-characterized withregard to Ca(super 2+) signaling properties. Stimulation of pancreatic acinar cells with the neurotransmitter acetylcholine or the hormone cholecystokinin evokes Ca(super 2+) signals that are either local or global, depending on the agonist concentration and the length of the stimulation period. The nature of the Ca(super 2+) transport events across the basal and apical plasma membranes as well as the involvement of the endoplasmic reticulum (ER), the nucleus, the mitochondria, and the secretory granules in Ca(super 2+) signal generation and termination have become much clearer in recent years.

Biological transport, Calcium, Calcium (Chemical element), Pancreas

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Building a cellular switch: more lessons from a good egg

Article Abstract:

Author's Abstract: COPYRIGHT 1999, John Wiley & Sons, Inc. Xenopus oocytes mature in response to the steroid hormoen progesterone. At the level of a population of oocytes, the response is graded--the higher the concentration of progesterone, the larger the fraction of oocytes that will mature--but at the level of the individual oocyte, the response is all-or-none. The all-or-none character of this cell fate switch is hypothesized to arise out of two properties of the signal transduction machinery that mediates maturation, positive feedback and ultrasensitivity. This combination of positive feedback plus ultrasensitivity crops up again and again in cellular switches, from the lysis-lysogeny switch in phage-infected bacterial to the action potential in neurons.

Cellular control mechanisms, Cell regulation

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Xenopus oocyte maturation: new lessons from a good egg

Article Abstract:

Author's Abstract: COPYRIGHT 1999, John Wiley & Sons, Inc. Fully grown Xenopus oocytes can remain in their immature state essentially indefinitely, or, in response to the steroid hormone progesterone, can be induced to develop intofertilizable eggs. This process is termed oocyte maturation. Oocyte maturation is initiated by a novel plasma membrane steroid hormone receptor. Progesterone brings about inhibition of adenylate cyclase and activation of the Mos/MEK1/p42 MAP kinase cascade, which ultimately brings about the activation of the universal M phase trigger Cdc2/cyclin B. Oocyte maturation provides an interesting example of how signaling cascades entrain the cell cycle clock to environmental changes.

Xenopus, Progesterone, Progesterone receptors

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