A functional role of the erg-like inward-rectifying K+ current in prolactin secretion from rat lactotrophs

The functional role of the inward-rectifying erg-like K+ current in rat lac totrophs was studied by the use of a selective blocker, the class III antia rrhythmic agent E-4031. The erg-like current was measured as drug-sensitive current in physiological K+ gradient. In the range of the normal resting m embrane potential of rat lactotrophs (around -45 mV) the erg-like current c onstituted a steady outward current. A selective block of this current by E -4031 resulted in a moderate (5 mV) depolarization of the membrane potentia l in 64% of the lactotroph cells. Measurements of basal prolactin secretion with the reverse hemolytic plaque assay showed that the number of prolacti n secreting cells and the amount of prolactin secreted from single lactotro phs was significantly increased in the presence of E-4031. The data show th at the contribution of the erg-like K+ current to the maintenance of the re sting membrane potential is functionally important for the regulation of pr olactin secretion. (C) 1999 Elsevier Science Ireland Ltd. All rights reserv ed.