125I-iodopindolol binding to frog esophageal peptic cells. Detection of amine uptake and beta-adrenergic receptors coupled to pepsinogen secretion.
The beta-adrenergic receptors (beta-ARs) coupled to pepsinogen secretion on frog esophageal peptic cells have been compared to frog erythrocyte beta-ARs using the radioligand 125I-iodopindolol (125I-PIN). 125I-PIN binding to intact peptic cells was time and temperature dependent. Saturation and competition experiments established that a large component of this binding represented radioligand uptake, which was energy dependent, pH sensitive, Na+ independent, and inhibited by agents that depress cellular ATP or disrupt proton gradients. This uptake system, which was absent from frog erythrocytes, appeared similar to that recently described for a number of mammalian cells. 125I-PIN bound to a single class of sites on peptic cell homogenates with a KD = 64 (+/- 5) pM. Binding to cell homogenates and a proportion of the binding to intact cells was inhibited by beta-agonists and antagonists with pharmacological characteristics similar to typical beta 2-ARs of frog erythrocytes. The number of beta-ARs in these peptic cell preparations was 1300 (+/- 240) sites/cell. Isolated peptic cells were poorly responsive to isoproterenol stimulation even in the presence of the phosphodiesterase inhibitor IBMX (3-isobutyl-1-methylxanthine). Pretreatment of cells with the phorbol ester TPA (12-O-tetra-decanoylphorbol-13-acetate) (100 nM) promoted isoproterenol stimulation of pepsinogen secretion. Catecholamine agonists stimulated pepsinogen secretion with an order of potency: isoproterenol greater than epinephrine much greater than norepinephrine, which was identical to that determined for inhibition of 125I-PIN binding. These findings indicate that frog peptic cells contain beta 2-ARs functionally coupled to pepsinogen secretion.
Dickinson
K E
KE
Division of Gastroenterology, University of Alabama, Birmingham 35294.
Anderson
W
W
Matsumoto
H
H
Uemura
N
N
Hirschowitz
B I
BI
D000818:Animals; D001679:Biogenic Amines / Q000378:metabolism*; D001692:Biological Transport; D004837:Epinephrine / Q000494:pharmacology; D004912:Erythrocytes / Q000378:metabolism; D004947:Esophagus / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D010435:Pepsinogens / Q000378:metabolism*; D010869:Pindolol / Q000031:analogs & derivatives* / Q000378:metabolism; D011892:Rana catesbeiana; D011943:Receptors, Adrenergic, beta / Q000032:analysis / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D001679:Biogenic Amines; D010435:Pepsinogens; D011943:Receptors, Adrenergic, beta; C029247:3-iodopindolol; D010869:Pindolol; D007545:Isoproterenol; D013755:Tetradecanoylphorbol Acetate; D004837:Epinephrine