INVOLVEMENT OF THE CA2+ CALMODULIN-DEPENDENT PROTEIN-KINASE-II PATHWAY IN THE CA2+-MEDIATED REGULATION OF THE CAPACITATIVE CA2+ ENTRY IN XENOPUS OOCYTES/

Activation of the phosphoinositide transduction pathway induces capaci tative Ca2+ entry in Xenopus oocytes. This can also be evoked by intra cellular injection of Ins(1,4,5)P-3, external application of thapsigar gin and/or incubation in a Ca2+-free medium. Readmission of Ca2+ to vo ltage-clamped, thapsigargin treated Xenopus oocytes triggers Ca2+-depe ndent Cl- current variations that reflect capacitative Ca2+ entry. Inh ibition of Ca2+/calmodulin-dependent protein kinase II (CaMKII) by spe cific peptides markedly increased the amplitude of the transients, sug gesting an involvement of the CaMKII pathway in the regulation of capa citative Ca2+ entry. Biochemical studies provide evidence for the acti vation of CaMKII in response to the development of capacitative Ca2+ e ntry. In effect, a CaMKII assay in vivo allows us to postulate that re admission of Ca2+ to thapsigargin-treated oocytes can induce a burst o f CaMKII activity. Finally, analysis of the Cl- transient kinetics at high resolution of time suggests that CaMKII inhibition blocks the ons et of the inactivation process without affecting the activation rate. We therefore postulate that CaMKII might participate in a negative fee dback regulation of store-depletion-evoked Ca2+ entry in Xenopus oocyt es.