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HORMONES AND SIGNALING

Cyclic AMP accelerates calcium waves in pancreatic acinar cells

¹Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut; and ²Internal Medicine, Michigan State University, East Lansing, Michigan

Submitted 26 September 2007 ; accepted in final form 2 April 2008

Cytosolic Ca²⁺ (Ca) flux within the pancreatic acinar cell is important both physiologically and pathologically. We examined the role of cAMP in shaping the apical-to-basal Ca²⁺ wave generated by the Ca²⁺-activating agonist carbachol. We hypothesized that cAMP modulates intra-acinar Ca²⁺ channel opening by affecting either cAMP-dependent protein kinase (PKA) or exchange protein directly activated by cAMP (Epac). Isolated pancreatic acinar cells from rats were stimulated with carbachol (1 µM) with or without vasoactive intestinal polypeptide (VIP) or 8-bromo-cAMP (8-Br-cAMP), and then Ca was monitored by confocal laser-scanning microscopy. The apical-to-basal carbachol (1 µM)-stimulated Ca²⁺ wave was 8.63 ± 0.68 µm/s; it increased to 19.66 ± 2.22 µm/s (*P < 0.0005) with VIP (100 nM), and similar increases were observed with 8-Br-cAMP (100 µM). The Ca²⁺ rise time after carbachol stimulation was reduced in both regions but to a greater degree in the basal. Lag time and maximal Ca²⁺ elevation were not significantly affected by cAMP. The effect of cAMP on Ca²⁺ waves also did not appear to depend on extracellular Ca²⁺. However, the ryanodine receptor (RyR) inhibitor dantrolene (100 µM) reduced the cAMP-enhancement of wave speed. It was also reduced by the PKA inhibitor PKI (1 µM). 8-(4-chloro-phenylthio)-2'-O-Me-cAMP, a specific agonist of Epac, caused a similar increase as 8-Br-cAMP or VIP. These data suggest that cAMP accelerates the speed of the Ca²⁺ wave in pancreatic acinar cells. A likely target of this modulation is the RyR, and these effects are mediated independently by PKA and Epac pathways.

calcium signaling; pancreatitis; zymogen activation; exocrine pancreas