Two types of calcium channels and hormone release in human pituitary tumor cells.
Voltage-gated Ca2+ channel currents were examined in human growth hormone-producing cells using the whole cell variation of patch electrode voltage clamp. In 20 mM Ba2+, Na+-free medium, the inward current was composed of a fast-inactivating component (transient type) and a steady component (long-lasting type). These two types had different properties. The transient type inactivated with the depolarizing prepulse but the long-lasting type did not. The transient type was activated at more negative potential levels than the long-lasting type. Deactivation kinetics of the transient type were slower than that of the long-lasting type. Nitrendipine inhibited and Bay K 8644 enhanced Ca2+ channel currents, and the effects of these agents were more prominent on the long-lasting type than on the transient type. Hormone release was inhibited by nitrendipine and enhanced by Bay K 8644, indicating involvement of Ca2+ influx through voltage-gated channels in the release process.
Yamashita
N
N
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
Matsunaga
H
H
Shibuya
N
N
Teramoto
A
A
Takakura
K
K
Ogata
E
E
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000236:Adenoma / Q000378:metabolism / Q000503:physiopathology*; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D013006:Growth Hormone / Q000378:metabolism*; D006462:Hemolytic Plaque Technique; D006801:Humans; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials; D009568:Nitrendipine / Q000494:pharmacology; D010911:Pituitary Neoplasms / Q000378:metabolism / Q000503:physiopathology*; D011388:Prolactin / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D007473:Ion Channels; D001464:Barium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D011388:Prolactin; D013006:Growth Hormone; D009568:Nitrendipine; D002118:Calcium