INTRACELLULAR AND WHOLE-CELL RECORDINGS FROM ZONA-FREE HAMSTER EGGS: SIGNIFICANCE OF LEAK IMPALEMENT ARTIFACT

Measurements have been made of membrane potential and input resistance of zona-free hamster eggs from single micro-electrode recordings. At room temperature (20-23 °C) the mean (±S.D.) values for the potential and resistance were -30 ± 8 mV and 280 ± 130 MC ( n = 94 eggs). At 37 °C the mean (±S.D.) values for the potential and resistance were -39 ± 13 mV and 230 ± 60 MΩ ( n = 60 eggs). The most negative potential recorded at room temperature was -51 mV in a cell which had an input resistance of 620 MΩ. At 37 °C six eggs out of sixty had potentials more negative than -50 mV and three of these gave all-or-none action potentials in response to depolarizing current pulses. In a separate series of experiments with high resistance micro-electrodes ( ca. 100 MΩ) six eggs out of twenty-one had potentials more negative than -50 mV and four of these were electrically excitable. Transient potential recordings during impalement indicated that the potential was more negative than -30 mV but that the insertion of a micro-electrode produced a leak pathway with a resistance of about 10 MΩ, substantially smaller than the steady-state estimates of the input resistance (see above). Whole-cell recordings with patch pipettes gave potentials in the range -30 to -80 mV and input resistances in the range 180 to 350 MΩ ( n = 8); four eggs gave action potentials in response to depolarizing current pulses passed through the patch pipette. It is concluded that the leak impalement artifact is so significant in micro-electrode recordings from hamster eggs that it prevents routine reliable potential measurements.