CALCIUM-EVOKED OPENING OF POTASSIUM CHANNELS IN HAMSTER EGGS

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Abstract
Measurements of membrane potential and resistance were made in zona-free hamster eggs. The resting potential lay in the range -9 to -100 mV and the input resistance fell in the range 14 to 440 M.OMEGA.; high resting potentials were associated with large input resistances. Ca injected ionophoretically into an egg from an intracellular micro-electrode caused a reduction of the membrane resistance. The estimated reversal potential for the Ca-evoked response was about -80 mV and its amplitude depended on the extracellular concentration of K but not on the Cl- concentration. Membrane K channels apparently open in response to a rise in the cytosolic concentration of Ca2+. Evidence is presented to suggest that micro-electrode recordings of the membrane potential and resistance of eggs suffer from an impalement leak artifact. The presence of the artifact lowers the resting potential and resistance of the cell so that intracellular Ca injection causes a hyperpolarization. A hyperpolarizing response to Ca would be unlikely in the absence of an impalement artifact.