Abstract
It was recently suggested that the opening of neutrophil plasma membrane Ca 2+ channels by chemotactic agents is mediated by a rise in free cytosolic Ca 2+ concentration ([Ca 2+] i). This hypothesis was tested in human cells monitoring [Ca 2+] i, with the indicator indo-1. In cells loaded with the Ca 2+-chelating agent bis( o-aminophenoxy)ethane- N, N, N′, N′-tetraacetate, transmembrane Ca 2+ uptake could be stimulated by formyl-methionyl-leucyl-phenylalanine (fMLP) even when [Ca 2+] i was at or below the resting level. In contrast, simply elevating [Ca 2+] i in unstimulated cells failed to increase transmembrane uptake. It was concluded either that Ca 2+ uptake across the plasma membrane is activated directly by the formation of the chemotactic factor-receptor complex or, more likely, that a transduction mechanism distinct from changes in [Ca 2+] i is involved.
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