IN-SITU RECORDINGS OF PRESUMED FOLLICULO-STELLATE CELLS IN THE INTERMEDIATE LOBE OF THE PITUITARY-GLAND OF XENOPUS-LAEVIS

In situ whole cell voltage clamp recordings of presumed folliculo-stel late cells were made in the intermediate lobe of the clawed toad Xenop us laevis. Lucifer Yellow fillings revealed, in addition to the small, spherical melanotropes, a population of larger cells with many proces ses that were, to a limited extent, dye-coupled and are assumed to be folliculo-stellate cells. The presumed folliculo-stellate cells differ ed strongly from the melanotropes in electrophysiological properties. The cells had a membrane resistance of <600 M Omega (at-100 to -80 mV) and a membrane potential of ca. -90 mV, close to the equilibrium pote ntial for K+. At potentials of greater than or equal to-20 mV, most of the cells displayed a rapidly activating and slowly inactivating outw ard K+ current, In all cells, hyperpolarizing pulses to less than or e qual to-100 mV activated an inward rectifying K+ current.