INOSITOL TRIPHOSPHATE PRODUCES DIFFERENT PATTERNS OF CYTOPLASMIC CA2+ SPIKING DEPENDING ON ITS CONCENTRATION

In single mouse pancreatic acinar cells the effects of intracellular infusion of inositol 1,4,5-trisphosphate (InsP3) or the non-metabolizable InsP3 analogue inositol 1,4,5-triphosphorothioate (InsPS3) have been investigated using a wide range of concentrations. Different types of cytosolic Ca2+ fluctuation patterns (monitored as Ca2+-dependent Cl- current in patch-clamp whole-cell recording experiments) could be generated by InsP3 or InsPS3, dependent on concentration, resembling those previously shown to be evoked by varying degrees of receptor activation in these cells. Low InsPS3 concentrations evoked repetitive local Ca2+ spikes whereas at relatively high concentrations repetitive Ca2+ waves were produced. In the presence of intracellular citrate a much lower messenger level was sufficient to generate waves. The InsP3 concentration determines whether the cytosolic Ca2+ signals are local or global.