Analysis of Agonist-Induced Cell Recruitment in Terms of Intracellular Calcium Mobilization in a Population of Enzymatically Dispersed Pancreatic Acinar Cells

Abstract

The term cell recruitment is often used to describe the accumulation of motile cells such as neutrophils, lymphocytes, macrophages and mast cells at the site of release of some chemotactic factor. In the broadest sense of the word, however, this term applies to every situation in which a signal mobilizes cells to perform some kind of cellular activity. For instance, in a population of enzymatically dispersed pancreatic acinar cells the peptide hormone cholecystokinin (CCK) both time- and dose-dependently increases the number of cells displaying repetitive changes in free cytosolic calcium concentration (Fig. 29.1). This particular experiment clearly demonstrates that only part of the cells respond to stimulation with a submaximal concentration of 10 pM of the COOH-terminal octapeptide of CCK (CCK₈), with a delay greatly differing between individual cells. As a result, maximal recruitment is reached only at 10 min following the onset of stimulation. By contrast, the vast majority of cells respond within the first minute of stimulation with a close to maximal hormone concentration of 1 nM. Such detection of differences in sensitivity among individual cells was enabled by the development of digital imaging techniques allowing simultaneous monitoring of agonist-induced changes in [Ca²⁺]_i in large numbers of individual cells loaded with Ca²⁺-sensitive fluorescent dye. This chapter aims to give a detailed description of the method used in our laboratory to analyze agonist-induced cell recruitment in terms of intracellular calcium mobilization.