Nature of the Role of Calcium in Secretion
The large body of evidence that we have considered links the pivotal action of calcium on the secretory process to exocytosis, which is a fusion-fission response involving the interaction of the plasma membrane and the secretory granule membrane. Membrane fusion is not confined to secretory cells but is a fundamental process in biological systems, involving the interaction of membranes of two different cells or membranes of the same cell. Cell fusion is observed in the presence of calcium, barium, or strontium, but not magnesium (Poste and Allison, 1973), strengthening the relationship between cell fusion and secretion and implying that elucidation of the basic and fundamental action of calcium in secretion might be sought in a better understanding of membrane fusion phenomena. While Palade (1959) was the first to recognize the importance of membrane fusion in the activation of the secretory process, DelCastillo and Katz proposed that there are specific and complementary sites on the synaptic vesicles and axonal membrane such that only when the two sites interact can membrane fusion and release of transmitter occur (Katz, 1969).
KeywordsSecretory Granule Secretory Cell Membrane Fusion Secretory Response Myosin Light Chain Kinase
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