Comparative effect of atropine on the adrenergic and muscarinic stimulation of phospholipid 32P labelling in isolated parotid cells: atropine, a possible blocker of alpha-adrenergic receptors.
The inhibitory effect of atropine on phospholipid 32P labelling stimulated by muscarinic or alpha-adrenergic agonists was studied in isolated parotid cells. Atropine (10(-11) to 10(-4) M) had no effect on phospholipid 32P labelling in unstimulated cells. In contrast, 10(-8) to 10(-7) M atropine provoked a competitive inhibition of the cholinergic stimulation (i.e. this effect was completely wiped out at high agonist concentration). The atropine app. KD for the muscarinic receptor was 5 X 10(-9) M. Moreover, atropine inhibits the adrenergic stimulation of phospholipid 32P labelling by decreasing the efficacity and potency of the adrenergic agonists. The atropine app. KD for the alpha-adrenergic receptor can be estimated at 10(-5) M. This inhibition of alpha-adrenergic stimulation appears to be specific since atropine was without effect on the substance P or beta-adrenergic stimulation. At very low concentration (10(-10) - 10(-9) M) atropine seems to be a modulator (activator) of the muscarinic or adrenergic agonist-receptor complex. From the present data, it is suggested that atropine, besides its classical blocker effect at the muscarinic receptor, at high concentration is a specific alpha-adrenergic antagonist.
D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D002217:Carbachol / Q000494:pharmacology; D002469:Cell Separation; D004837:Epinephrine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010743:Phospholipids / Q000096:biosynthesis*; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000502:physiology; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000502:physiology
D010710:Phosphates; D010743:Phospholipids; D011942:Receptors, Adrenergic, alpha; D011976:Receptors, Muscarinic; D001285:Atropine; D002217:Carbachol; D009638:Norepinephrine; D004837:Epinephrine