Muscarinic receptors of the albino rabbit ciliary process.
Muscarinic receptor binding sites were identified in membranes prepared from albino rabbit ciliary processes, using the muscarinic antagonist [3H]L-quinuclidinyl benzylate as the radioligand. Analysis of saturation binding experiments demonstrated that [3H]L-quinuclidinyl benzylate bound to an apparent homogeneous population of binding sites with a Kd value of 6.4 pm and a Bmax value of 155 fmol mg-1 protein. Seventy percent (70%) of binding sites showed high affinity for pirenzepine, i.e. belonged to the M1 subtype. In contrast, AF-DX 116 was unable to discriminate between subtypes of muscarinic binding sites in this tissue. Carbachol caused a dose-dependent increase in phosphatidylinositol turnover (EC50 = 154 microM) in ciliary processes. A maximum stimulation of 652% of basal activity was obtained following a 45 min incubation with 10 mM carbachol. The potency of muscarinic antagonists to block the carbachol-induced response was comparable to that found for M1 receptors in other tissues. Oxotremorine and pilocarpine behaved like partial agonists in this assay. The carbachol-induced increase in phosphatidylinositol turnover was also observed in a suspension of epithelial cells from ciliary processes and it was blocked by atropine; thus, indicating the presence of muscarinic receptors functionally coupled to phosphatidylinositol turnover in these cells.
Mallorga
P
P
Merck Sharp and Dohme Research Laboratories, West Point, PA 19486.
Babilon
R W
RW
Buisson
S
S
Sugrue
M F
MF
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002924:Ciliary Body / Q000378:metabolism*; D010277:Parasympathomimetics / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011817:Rabbits; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*
D010277:Parasympathomimetics; D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate; D002217:Carbachol