[Ca]i-reducing action of cAMP in rat pancreatic b-cells: involvement of thapsigargin-sensitive stores

Yaekura, Kazuro, and Toshihiko Yada. [Ca]i-reducing action of cAMP in rat pancreatic b-cells: involvement of thapsigargin-sensitive stores. Am. J. Physiol. 274 (Cell Physiol. 43): C513–C521, 1998.—In the present study, we examined the ability of adenosine 38,58-cyclic monophosphate (cAMP) to reduce elevated levels of cytosolic Ca21 concentration ([Ca]i) in pancreatic b-cells. [Ca]i and reduced pyridine nucleotide, NAD(P)H, were measured in rat single b-cells by fura 2 and autofluorescence microfluorometry. Sustained [Ca]i elevation, induced by high KCl (25 mM) at a basal glucose concentration (2.8 mM), was substantially reduced by cAMP-increasing agents, dibutyryl cAMP (DBcAMP, 5 mM), an adenylyl cyclase activator forskolin (10 μM), and an incretin glucagon-like peptide-1-(7–36) amide (1029 M), as well as by glucose (16.7 mM). The [Ca]ireducing effects of cAMP were greater at elevated glucose (8.3–16.7 mM) than at basal glucose (2.8 mM). An inhibitor of protein kinase A (PKA), H-89, counteracted [Ca]i-reducing effects of cAMP but not those of glucose. Okadaic acid, a phosphatase inhibitor, at 10–100 nM also reduced sustained [Ca]i elevation in a concentration-dependent manner. Glucose, but not DBcAMP, increased NAD(P)H in b-cells. [Ca]ireducing effects of cAMP were inhibited by 0.3 μM thapsigargin, an inhibitor of the endoplasmic reticulum (ER) Ca21 pump. In contrast, [Ca]i-reducing effects of cAMP were not altered by ryanodine, an ER Ca21-release inhibitor, Na1-free conditions, or diazoxide, an ATP-sensitive K1 channel opener. In conclusion, the cAMP-PKA pathway reduces [Ca]i elevation by sequestering Ca21 in thapsigargin-sensitive stores. This process does not involve, but is potentiated by, activation of b-cell metabolism. Together with the known [Ca]iincreasing action of cAMP, our results reveal dual regulation of b-cell [Ca]i by the cAMP-signaling pathway and by a physiological incretin.