Activation of beta-adrenergic receptors inhibits Ca2+ entry-mediated generation of inositol phosphates in the guinea pig myometrium, a cyclic AMP-independent event.
In the guinea pig myometrium, carbachol, oxytocin, and fluoroaluminates stimulated the breakdown of phosphatidylinositol 4,5-bisphosphate, which was insensitive to pertussis toxin [Biochem. J. 255:705-713 (1988)]. We now demonstrate that an increased accumulation of inositol phosphates, with an early production of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], could also be obtained with K+ (30 mM) and the Ca2+ ionophore ionomycin. Removal of extracellular Ca2+ or addition of the Ca2+ channel antagonists nifedipine and verapamil almost totally abolished stimulations elicited by high K+ and partially attenuated receptor- and fluoroaluminate-mediated increases in inositol phosphates. Isoproterenol similarly attenuated the accumulation of inositol phosphates elicited by carbachol, oxytocin, and fluoroaluminates (maximal inhibition, 35%; EC50, 0.5 nM), with no change in the rate of Ins(1,4,5)P3, inositol bisphosphate, and inositol monophosphate generation. The beta-adrenergic receptor-induced inhibition was prevented by pertussis toxin and could not be reproduced by forskolin, indicating that cAMP was not involved. Experimental findings were, rather, consistent with a predominant role for Ca2+. Thus, inhibition due to isoproterenol was lost in a Ca(2+)-depleted medium and was not additive with that caused by nifedipine. Accumulation of inositol phosphates triggered by high K+ was insensitive to the beta-adrenergic receptor inhibition. The inhibitory effect of isoproterenol, similar to that of nifedipine, was counteracted by ionomycin and also by the Ca2+ channel agonist Bay K 8644. These data indicate that in the myometrium 1) phospholipase C can be activated through a voltage-gated Ca2+ entry-dependent process that contributes at least partially to the stimulations triggered by receptor- and/or guanine nucleotide-binding protein-mediated activation and 2) beta-adrenergic receptor activation is linked via a cAMP-independent, pertussis toxin-sensitive pathway to an inhibition of voltage-gated Ca2+ channels, resulting in an attenuation of the Ca(2+)-associated generation of inositol phosphates.
Khac
L D
LD
Endocrinologie et Régulations Cellulaires, CNRS URA, Université Paris Sud, Orsay, France.
Mokhtari
A
A
Renner
M
M
Harbon
S
S
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000535:Aluminum / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002217:Carbachol / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004336:Drug Antagonism; D005260:Female; D005461:Fluorine / Q000378:metabolism; D006168:Guinea Pigs; D007295:Inositol Phosphates / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D009215:Myometrium / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D010121:Oxytocin / Q000378:metabolism; D037342:Pertussis Toxin; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015220:Calcium Channels; D007295:Inositol Phosphates; D011943:Receptors, Adrenergic, beta; D010566:Virulence Factors, Bordetella; D005576:Colforsin; C053629:fluoroaluminum; D005461:Fluorine; D010121:Oxytocin; D015759:Ionomycin; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002217:Carbachol; D014700:Verapamil; D000535:Aluminum; D000242:Cyclic AMP; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D009543:Nifedipine; D007545:Isoproterenol; D002118:Calcium