Measurement of cytosolic free calcium concentration in relation to insulin release in normal rat pancreatic islets.
The effects of glucose (16.7 mM), potassium (50 mM), forskolin (20 microM), dibutyryl cyclic AMP (1 mM) and arachidonic acid (82 microM) upon insulin release and cytosolic free calcium concentrations ([Ca2+]i) were investigated in normal rat pancreatic islets. Potassium, forskolin and dibutyryl cyclic AMP significantly raised [Ca2+]i, but elicited only minimal insulin release. In the absence of extracellular Ca2+, glucose evoked insulin release, but failed to augment [Ca2+]i. Arachidonic acid increased [Ca2+]i both in Ca-depleted and -repleted medium, but promoted insulin release only in Ca2+-repleted environment. These new observations clearly demonstrate by direct measurements that although [Ca2+]i is an important factor in exocytotic insulin release, its effect is subject to amplification or antagonism.