title: Electrical excitability in the rat clonal pituitary cell and its relation to hormone secretion.
abstract: Membrane electrical properties of the clonal anterior pituitary cell (GH3), were studied using intracellular recording techniques. The resting potential in the GH3 cell was -48.0 +/- 1.1 mV (mean +/- S.E., n=39) in normal saline. The input resistance estimated from the linear portion of the current-voltage relationship was 453 +/- 30 Momega (n=21). The maximum rate of rise of the action potential was 7.0 +/- 1.1 V/sec (n=12) at room temperature (23-25 degrees C). The action potential had both Na and Ca components. The Ca component was abolished by addition of 4 mM Co2+. Sr2+ could substitute for Ca2+ in supporting spike initiation. As the concentration of Sr2+ was increased, the maximum rate of rise of the action potential increased. After replacement of Ca2+ with isomolar Ba2+ the membrane potential shifted to -6.1 +/- 1.1 mV (n=11). In the Ba solution, prolonged action potentials were evoked by a depolarizing current pulse after maintaining the membrane potential more negative than -50 mV. The release of both prolactin and growth hormone was enhanced by increasing the external K+ concentration to 50 mM in the presence of Ca2+. Sr2+ could substitute for Ca2+. Ba2+ enhanced the release of both hormones, even if the K+ concentration was unaltered. The facilitatory effects of high K+ and Ba2+ were markedly suppressed by addition of 2-4 mM Co2+. These results may suggest that the potential-dependent increase in the membrane permeability to Ca2+, responsible for initiation of the Ca spike, plays a significant role in stimulation of hormone secretion in GH3 cells.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002999:Clone Cells; D013006:Growth Hormone / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000166:cytology*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000494:pharmacology
chemical_list: D001464:Barium; D011388:Prolactin; D013006:Growth Hormone; D012964:Sodium; D002118:Calcium