Xenopus tropicalis oocytes as an advantageous model system for the study of intracellular Ca 2+ signalling

The purpose of this study was to compare oocytes from the pipid frogs Xenopus tropicalis and Xenopus laevis , with respect to their utility for studying Ca 2+ signalling mechanisms and for expression of heterologous proteins. We show that X. tropicalis oocytes possess an intracellular Ca 2+ store that is mobilized by inositol (1,4,5) trisphosphate (IP 3 ). Ca 2+ signalling is activated by endogenous lysophosphatidic acid receptors and cytosolic Ca 2+ activates a plasma membrane chloride conductance. The spatiotemporal organization of cytosolic Ca 2+ signals, from the microscopic architecture of elementary Ca 2+ ‘puffs’ to the macroscopic patterns of Ca 2+ spiking are closely similar to the local and global patterns of Ca 2+ release previously characterized in oocytes from X. laevis . By injecting X. tropicalis oocytes with cDNA encoding an ER‐targeted fluorescent protein construct, we demonstrate the capacity of the X. tropicalis oocyte to readily express heterologous proteins. The organization of ER is polarized across the oocyte, with the IP 3 ‐releaseable store targeted within an ∼8 μm wide band that circumscribes the cell. We conclude that the X. tropicalis oocyte shares many of the characteristics that have made oocytes of X. laevis a favoured system for studying Ca 2+ signalling mechanisms. Moreover, X. tropicalis oocytes display further practical advantages in terms of imaging depth, Ca 2+ signal magnitude and electrical properties. These further enhance the appeal of X. tropicalis as an experimental system, in addition to its greater amenability to transgenic approaches.British Journal of Pharmacology (2001) 132 , 1396–1410; doi: 10.1038/sj.bjp.0703922