An inactivating inward-rectifying K current present in prolactin cells from the pituitary of lactating rats.
Primary cultures containing a high percentage of lactotrophs were obtained by dissociating the pituitary of rats following 14-18 days of lactation. Lactotrophs with a distinctive appearance were recorded after 1-35 days in vitro and identified by immunocytochemical staining for prolactin. Whole-cell voltage clamp measurements in isotonic KCl solution from a holding potential of -40 mV revealed the presence of inward-rectifying K currents with a time-dependent, Na(+)-independent inactivation at potentials negative to -60 mV. The time for complete inactivation was strikingly different between lactotrophs, varying between 1 sec and more than 5 sec at -120 mV, and was not related to time in culture. The reversal potential shifted 59 mV (25 degree C) for a tenfold change in external K+ concentration, demonstrating the selectivity of the channel for K+ over Na+. The inward-rectifying K current was blocked by 5 mM Ba2+ and partially blocked by 10 mM TEA. Chloramine-T (1 and 2 mM) produced a total block of the inward-rectifying K current in lactotrophs. Thyrotropin-releasing hormone (500 nM) significantly reduced the inward-rectifying K current in about half of the lactotrophs. This current is similar to the inward-rectifying K current previously characterized in clonal somatomammotrophic pituitary cells (GH3B6). The variability of the rate of inactivation of this current in lactotrophs and its responsiveness to TRH is discussed.
Corrette
B J
BJ
Physiologisches Institut, Universitätskrankenhaus Eppendorf, Hamburg, Germany.
Bauer
C K
CK
Schwarz
J R
JR
D000818:Animals; D001464:Barium / Q000378:metabolism; D002700:Chloramines / Q000494:pharmacology; D005260:Female; D007774:Lactation / Q000378:metabolism*; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D012964:Sodium / Q000378:metabolism; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014105:Tosyl Compounds / Q000494:pharmacology
D002700:Chloramines; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D013757:Tetraethylammonium Compounds; D014105:Tosyl Compounds; C016300:chloramine-T; D001464:Barium; D019789:Tetraethylammonium; D011388:Prolactin; D012964:Sodium; D011188:Potassium