Voltage activated ionic currents in gonadotrophs of the ovine pars tuberalis

Using whole cell recordings of membrane current and voltage from pars tuberalis gonadotrophs, we have examined the basis of membrane excitability in these cells. This technique allows internal perfusion of gonadotrophs, which has permitted the cell to be filled with CsCl solutions, thus removing outward components of K+ current. Under these conditions, tetrodotoxin (TTX)-sensitive Na+ or TTX-insensitive Ca2+ currents on the order of 500 and 100 pA, respectively, could be detected when the membrane potential was depolarised. Na+ currents, however, were at least 50% inactivated at the normal resting membrane potential of the gonadotroph, and required at least 2 s to recover from inactivation. These data provide the first direct observations of voltage-activated ionic currents in pituitary gonadotrophs, and may explain the TTX insensitivity of LH secretion.