Histamine evoked sustained elevations of cytosolic Ca2+ in bovine adrenal chromaffin cells independently of Ca2+ entry

Whole-cell patch-clamp experiments and optical measurements with the Ca2+ fluorescent dye fura-2 were performed to examine histamine induced cytosolic Ca2+ changes in bovine adrenal chromaffin cells. The purpose of this study was to find out whether the sustained plateau phase, which followed the rapid transient increase, was due to Ca2+ influx. The extracellular Ca2+ dependence appeared to be minor, because substitution of Ca2+ with EGTA or BAPTA did not cause obvious changes in the biphasic Ca2+ response. Application of histamine in a Mn2+ containing external solution did not quench the fura-e signal. it was neither possible to detect a histamine induced depolarisation, nor a Ca2+ permeable current. Changing the driving force for Ca2+ during the plateau phase did not result in a correlating fura-2 signal. Metal ions like Cd2+, La3+ and Co2+ which are known to block Ca2+ influx were unable to abolish the typical histamine induced Ca2+ response. These results suggest that primarily intracellular Ca2+ was responsible for generating the characteristic biphasic Ca2+ response due to histamine in bovine adrenal chromaffin cells. (C) 2000 Harcourt Publishers Ltd.