Propagating potassium and chloride conductances during activation and fertilization of the egg of the frog, Rana pipiens.

Abstract

SUMMARY1. Fertilization or artificial activation of the frog egg (Rana pipiens) elicits a positive-going shift in membrane potential which results from an opening of Cl-and K+ channels in the egg membrane. We examined the spatial localization of the currents produced by the opening of these channels, using large patch electrodes (tip diameters 3-10 ,um). We also used small patch electrodes (tip diameters about 1 /Im) to study the single K+ channel currents.2. After activation, with the patch electrode at any position on the egg surface, we observed a transient current, with a main peak lasting several seconds. This activation current occurred after a variable delay of 0-3 min following the rise of the activation potential. With 10 % Ringer solution in the bath and pipette, the current was usually outward, although it sometimes had an inward component.3. With one patch electrode on the animal surface of the egg and another patch electrode on the vegetal surface, we observed that the activation current propagated over the egg surface. In experiments where the egg was activated by applying a hyperpolarizing pulse, the response in the animal half preceded that in the vegetal half by an average of about 1 min. The amplitude of the peak outward current was similar for animal and vegetal recordings (1-2 mA/cm2).4. Tetraethylammonium (11 mM) in the patch pipette blocked most ofthe outward component of the activation current and revealed an underlying inward component.5. The inward component of the activation current was carried by Cl-, since it could be reversed by raising the Cl-concentration in the pipette.6. The Cl-component of the activation current propagated over the egg surface, with timing similar to that of the total current. 7. The average amplitude of the peak Cl-current was six or more times larger at the animal than the vegetal surface.8. Fertilization caused a current to propagate from the animal to the vegetal surface, like the current observed during activation.9. With a small patch electrode, single channel currents of the K+ component of the activation current could be seen. The probability that the channels were open increased at more positive potentials. The single channel conductance was estimated 8-2 228 L. A. JAFFE, R. T. KADO AND L. MUNCY to be 25 pS, and the reversal potential to be -150 mV. Single Cl-channel currents have not yet been seen.10. Activation or fertilization of the frog egg resulted in a wave-like opening of Cl-and K+ channels, which spread from the animal to the vegetal half of the egg. The Cl-conductance was larger on the animal half.

Molecular cloning and developmental expression of two Chloride Intracellular Channel (CLIC) genes in Xenopus laevis

“…This was confirmed by RT-PCR analysis of early blastulas divided into animal and vegetal halves, using equal amounts of extracted mRNA (determined by amplifying the ubiquitous ornithine decarboxylase transcript; data not shown). These observations are consistent with a role for Cl --channel-mediated membrane potential changes to prevent polyspermy following fertilisation (Jaffe et al 1985). By stage 7, xCLIC transcripts appear to be localised to the centre of animal hemisphere cells (Fig.…”

The electrical block to polyspermy induced by an intracellular Ca2+ increase at fertilization of the clawed frogs, Xenopus laevis and Xenopus tropicalis

“…A small inward IS current occurred in 20 mM NaCl (g), but only outward IS current was generated in 20 mM NaI (h), indicating that not only the large and accelerative increase in inward current but also the IS current results from the opening of Clchannels on the egg plasma membrane. SB: tropicalis eggs is probably mediated by a wavelike opening of Cl − channels in response to the Ca 2+ wave, observed in frog fertilization (Jaffe, Kado, & Muncy, 1985;Kline & Nuccitelli, 1985). Thus, we found that monospermic fertilization of X. tropicalis was ensured by the positive-going fertilization potential which was mediated by the opening of CaCCs.…”

“…CaCCs on egg plasma membrane are probably activated in response to the Ca 2+ wave spreading from the sperm entry site because the positive‐going activation potentials similar to the fertilization potentials were elicited by an artificial increase in [Ca 2+ ] i with Ca 2+ ‐ionophore. The positive fertilization potential in X. tropicalis eggs is probably mediated by a wavelike opening of Cl − channels in response to the Ca 2+ wave, observed in frog fertilization (Jaffe, Kado, & Muncy, ; Kline & Nuccitelli, ). Thus, we found that monospermic fertilization of X. tropicalis was ensured by the positive‐going fertilization potential which was mediated by the opening of CaCCs.…”

A calcium influx is triggered and propagates in the zygote as a wavefront during in vitro fertilization of flowering plants

“…By contrast, during fertilization in animals, studies have allowed the recording only of membrane currents and not that of the ions carrying them (30,31). Furthermore, most of these studies were performed with artificially activated rather than sperm-activated eggs (32). Sea urchin is the only system where current propagation was analyzed in detail during fertilization.…”