. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 116 G. R. WINKEL AND R. NUCCITELLI. Figure 5. Composite diagram of the ionic current pattern in the mouse embryo. The current is outward along the embryonic midline. while the maximal outward current is primarily over the fore- gut. This transembryonic current will then complete the current loop returning as inward current via the extraembryonic endoderm. they may not have had access to internal epithelia. Therefore in future experiments we plan to inject ATP- ase inhibitors and channel-blocking drugs into the amni-
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 116 G. R. WINKEL AND R. NUCCITELLI. Figure 5. Composite diagram of the ionic current pattern in the mouse embryo. The current is outward along the embryonic midline. while the maximal outward current is primarily over the fore- gut. This transembryonic current will then complete the current loop returning as inward current via the extraembryonic endoderm. they may not have had access to internal epithelia. Therefore in future experiments we plan to inject ATP- ase inhibitors and channel-blocking drugs into the amni- otic cavity to bypass this limitation. Furthermore, we would like to determine which ionic species are responsi- ble for the majority of the ionic current. Thus we are con- ducting ionic substitution experiments to establish the ionic character of these currents (Winkel and Nuccitelli, 1987). The morphology of the endoderm overlying the primi- tive streak and anterior to the head process had little rela- tionship to the detected current pattern. In scanning elec- tron micrographs, the cells in the midline appear contin- uous from the foregut, where the outward current is greatest, to the archenteron where the outward current is reduced. Despite the fact that there is a hiatus in the endoderm at the archenteron, as the cells of the head pro- cess emerge (Poelman, 1981; Tarn and Meier. 1982), the outward currents are not affected by this morphological discontinuity. Therefore, changes in morphology overly- ing the embryonic regions of the mouse embryo are ap- parently unrelated to the ionic and junctional changes occurring within the epithelium. The ionic current pattern demonstrated here may be indicative of a morphogenetic event, such as gastrulation in the mouse embryo, and may even be influencing mor- phogenetic cellular rearrangements as gastrulation pro- ceeds. The currents we detected are strong ionic currents. Currents on the order of 20 to 40 j/A/cm2 recorded 20 nM from
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