Transitional changes in membrane potential and intracellular [Ca2+] in ratbasophilic leukemia cells

Using whole-cell current-clamp measurements we have found that thapsigargin -mediated activation of store-regulated Ca2+ entry in rat basophilic leukem ia cells is accompanied by complex changes in membrane potential. These cha nges consisted of: (i) an initial slow, small depolarization, (ii) a transi tional change in potential to a depolarized value and (iii) transitional ch anges between a hyperpolarized and a depolarized potential. These complex c hanges in potential can be explained by the interaction between the endogen ous inwardly rectifying K+ conductance and the generation of a small inward current. To investigate the possible influence of these changes of potenti al on [Ca2+](i), single cell measurements of fura2 fluorescence were undert aken alone or in combination with current-clamp measurements. Thapsigargin- mediated activation of the store-regulated Ca2+ entry pathway was accompani ed by a marked increase of [Ca2+](i). During this increase, transient, abru pt declines in [Ca2+](i) were detected in approximately 60% of the cells in vestigated. These changes of [Ca2+](i) are consistent with the observed cha nges of membrane potential recorded under current-clamp.