A variety of nammalian cells exhibit membrane potential oscillations composed of repeated hyperpolarizations. Such hyperpolarizing oscillations are usually caused by cyclic increases in the cytosolic Ca
2+ ions, which in turn, periodically stimulate Ca
2+-activated K
+ channels. Intracellular Ca
2+ oscillations could be brought about by a feedback relationship between an autocatalytic Ca
2+ input and a delayed Ca
2+ output. In mouse fibroblastic L cells, the operation of Ca
2+ channels and that of Ca
2+ pump are involved in the oscillations. The Ca
2+ channels are activated by stimulation of membrane receptors to complement components (such as Clq) and nucleotides (such as ATP), which are chemotactic factors for the firboblasts. In human epithelial Intestine 407 cells, stimulation of receptors to intestinal secretagogues (such as acetylcholine, histamine, serotonin and VlP) gives rise to Ca
2+ release from some intracellular calcium stores. Under appropriate conditions, receptor stimulation by agonists was found to lead to generation of the oscillations in both cell species. Thus, it is strongly suggested that oscillations of membrane potential and cytosolic Ca
2+ occur in the recepor-activated fibroblasts and enterocytes in vivo, and that the oscillations play an important role in Ca
2+-mediated cell activities such as fibroblast chemotaxis and intestinal secretion.
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