Characteristics of Ba2+-stimulated insulin release with special reference to pancreatic beta-cells sensitized by cyclic AMP.

Ca2+-dependent processes are activated by Ba2+ in a variety of biological systems. When Ca2+ was replaced by equimolar amounts of Ba2+ there was a marked increase in insulin secretion from beta-cell-rich pancreatic islets microdissected from ob/ob-mice. At both 3 and 20 mM glucose Ba2+ stimulated insulin release in a concentration-dependent manner, being less stimulatory at high concentrations. The stimulatory effect of Ba2+ on insulin release is similar to that of Ca2+ in being more pronounced and reached at lower concentrations when the beta-cells were sensitized by cyclic AMP. However, both glucose oxidation and utilization were suppressed when Ca2+ was replaced by equimolar amounts of Ba2+. Ba2+-stimulated insulin release resembled physiological secretion initiated by Ca2+ in being inhibited by L-epinephrine, pentobarbital and a low oxygen tension.