Abstract
The chick blastoderm at the stage of late gastrula is a flat disc formed by three cell layers and exhibiting epithelial properties. Blastoderms were cultured in miniature chambers and their electrophysiological characteristics were determined under Ussing conditions.
Under open-circuit condition and identical physiological solutions on both sides, spontaneous transblastodermal potential difference (V oc) of −7.5±3.3 mV (ventral side positive) was measured. Under short-circuit condition (transblastodermal ΔV = 0 mV), the blastoderm generated short-circuit current (I sc) of 21±8 μA/cm2, which was entirely dependent on extracellular sodium, sensitive to ouabain applied ventrally and independent of extracellular chloride. The net transblastodermal Na+ flux fully accounted for the measured I sc, both under control conditions and with ouabain. The total transblastodermal resistance (R tot) was 390±125 Ωcm2.
Frequently, the V oc, I sc and R tot showed spontaneous oscillations with a period of 4–5 min. Removal of endoderm and mesoderm did not significantly affect the electrical properties, indicating that the electrogenic sodium transport is generated by the ectoderm.
The V oc and I sc measured in the area pellucida (−1.3±0.8 mV, 9.3±4.4 μA/cm2) and extraembryonic area opaca (−7.8±1.1 mV, 31.2±12.7 μA/cm2) were significantly different. Such a heterogeneous distribution of electrical properties can explain the presence in the blastoderm of extracellular electrical currents found by using a vibrating probe.
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This work was supported by the Swiss National Research Foundation (grant. 3.418-0.86 to P.K.) and by Roche Research Foundation (grant. to U.K.). We thank Drs. E. Raddatz and Y. de Ribaupierre for helpful discussions.
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Kučera, P., Abriel, H. & Katz, U. Ion transport across the early chick embryo: I. Electrical measurements, ionic fluxes and regional heterogeneity. J. Membarin Biol. 141, 149–157 (1994). https://doi.org/10.1007/BF00238248
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DOI: https://doi.org/10.1007/BF00238248