Free calcium and calmodulin levels in acinar carcinoma and normal acinar cells of rat pancreas

Altered calcium signaling in cancer cells

It is the nature of the calcium signal, as determined by the coordinated activity of a suite of calcium channels, pumps, exchangers and binding proteins that ultimately guides a cell's fate. Deregulation of the calcium signal is often deleterious and has been linked to each of the 'cancer hallmarks'. Despite this, we do not yet have a full understanding of the remodeling of the calcium signal associated with cancer. Such an understanding could aid in guiding the development of therapies specifically targeting altered calcium signaling in cancer cells during tumorigenic progression. Findings from some of the studies that have assessed the remodeling of the calcium signal associated with tumorigenesis and/or processes important in invasion and metastasis are presented in this review. The potential of new methodologies is also discussed. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

A positive association between agonist-induced cyclic AMP production in vitro and metastatic potential in murine B16 melanoma and hamster fibrosarcoma

A positive association between agonist-stimulated cyclic AMP production in vitro and both experimentally induced (B16 melanoma) and spontaneous (fibrosarcoma) metastases were found. Five B16 melanoma cell lines producing varying degrees of lung colonization following intravenous injection and three hamster fibrosarcoma cell lines producing a varying number of metastases in lungs and regional lymph nodes after removal of the primary tumour were studied. Agonist-stimulated (forskolin and melanocyte-stimulating hormone), but not basal cyclic AMP accumulation, increased with increasing metastatic potential. This relationship did not extend to other intracellular signalling systems as determined by investigation of basal or foetal-calf stimulated phosphatidylinositol hydrolysis for either tumour type. Intracellular free calcium was also similar in B16 melanoma cell lines of varying metastatic potential.

Regulating transient and sustained changes of cytosolic Ca2+ in rat pancreatic acini

The regulation of changes in cytosolic Ca2+ concentration (Cai2+) during exposure to carbachol was studied in rat pancreatic acini loaded with fura-2. With an extracellular Ca2+ concentration (Cao2+) of 2.5 mM, resting Cai2+ is 185 +/- 48 (SD) nM (n = 23), which rises to 696 +/- 222 nM, then falls over 2 min to a stable plateau of 401 +/- 106 nM. With Cao2+ less than 10 nM, carbachol produces an immediate threefold increase in Cai2+ that dissipates over 2-3 min, and Cai2+ steadily falls below prestimulation levels. Atropine prevents all responses to carbachol, and when it is added during a response to carbachol, Cai2+ drops to resting values within seconds. Ca2+ influx is required for the prolonged elevation of Cai2+ during carbachol exposure, but Ca2+ entry is not regulated by an increase in Cai2+ itself nor does Ca2+ enter via voltage-gated L-type channels. The muscarinic receptor-operated Ca2+ entry mechanism is sensitive to Cao2+, since sustained elevations in Cai2+ are maximal at 2.5 mM Cao2+ but are much less pronounced at lower external Ca2+ concentrations.