Relationship Between Membrane Potential and Progesterone Release in Ovine Corpora Lutea

Abstract

When slices of ovine luteal tissue were perfused with medium containing luteinizing hormone (LH), the output of progesterone was increased significantly (P < 0.01) in 11 of 12 experiments. Addition of LH to the medium did not influence the luteal cell membrane potential. The addition of 47 mM K to the medium increased progesterone output (P < 0.01) and depolarized the luteal cell membrane within 2 min. Progesterone output decreased to approximate pretreatment levels within 2 min of the return to normal K levels in the perfusion medium. High levels of K further increased the output of progesterone from tissue stimulated with LH. Perfusion of the slices with Na-free medium increased (P < 0.01) progesterone output within 2 min, which returned to pretreatment levels within 2 min after normal Na levels were restored to the medium. Perfusion of the slices with Na-free medium did not influence the membrane potential. Perfusion of the tissue with LH, 47 mM K, or Na-free medium had no effect on progesterone output if the medium was Ca-free and/or contained 2 mM EGTA [ethylenebis(oxyethylenenitrilo)tetraacetic acid]. The Ca ion probably plays an important role in mediating the steroidogenic response of ovine luteal tissue to LH. A 2nd series of experiments was designed to ascertain if luteal cells were coupled electrically. Sixty-six pairs of luteal cells separated by 150-300 .mu.m were penetrated with electrodes, and the membrane potential of both cells was studied. One cell of each pair was hyperpolarized by passage of 0.4 nA current into the cell, but in no case was there an effect on the membrane potential of the other penetrated cell. When 5 cells were injected iontophoretically with Procion Yellow there was no evidence of diffusion of the dye to adjacent cells. There was no evidence which suggested that ovine luteal cells were coupled electrically.