Are Ca2+ channels in neutrophils activated by a rise in cytosolic free Ca2+?

Abstract

It was recently suggested that the opening of neutrophil plasma membrane Ca²⁺ channels by chemotactic agents is mediated by a rise in free cytosolic Ca²⁺ concentration ([Ca²⁺]_i). This hypothesis was tested in human cells monitoring [Ca²⁺]_i, with the indicator indo‐1. In cells loaded with the Ca²⁺‐chelating agent bis(o‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetate, transmembrane Ca²⁺ uptake could be stimulated by formyl‐methionyl‐leucyl‐phenylalanine (fMLP) even when [Ca²⁺]_i was at or below the resting level. In contrast, simply elevating [Ca²⁺]_i in unstimulated cells failed to increase transmembrane uptake. It was concluded either that Ca²⁺ 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 [Ca²⁺]_i is involved.