Covariance of ion flux measurements allows new interpretation of Xenopus laevis oocyte physiology

An animal-vegetal net ionic current identified previously using voltage probe techniques in maturing Xenopus laevis oocytes has now been investigated using noninvasive ion-selective microelectrodes. Three-dimensional fluxes of hydrogen (H+), potassium (K+), and bicarbonate (HCO3-) were characterized with respect to the developmental stage and hemisphere of the oocyte and presence of surrounding follicular tissue. Variable effluxes of H+ and HCO3- were recorded from both the animal and vegetal hemispheres. Variable influxes and effluxes of K+ were also observed. The equatorial region, silent by voltage probe, exhibited fluxes of H+ and K+. Simultaneous measurement of pairs of ions allowed correlation analysis of two ion types. Notably for H+ and K+ data, positive and negative correlation at animal and vegetal poles respectively offer an explanation of the unpredictable results obtained when individual ions were observed independently. J. Exp. Zool. 290:652-661, 2001. (C) 2001 Wiley-Liss, Inc.