EFFECTS OF MUSCARINIC AGENTS ON CULTURED HUMAN TRABECULAR MESHWORK CELLS

Intracellular calcium measurements were performed in cultured human tr abecular meshwork cells preloaded with the cell permeant dye fura 2-AM . Fluctuations in calcium levels were then monitored with microscope-b ased ratio fluorometry. Carbachol increased intracellular calcium in a dose-dependent manner; as did oxotremorine-M, aceclidine, and pilocar pine. Carbachol's effect was blocked by the non-selective muscarinic a ntagonist atropine, as well as by muscarinic receptor subtype-selectiv e antagonists such as pirenzepine (M(1)-selective), p-fHHSiD (M(3)-sel ective), and 4-DAMP (M(1), M(3) subtypes). Rank order of potencies for the antagonists' effects was atropine = 4-DAMP > p-fHHSiD > pirenzepi ne, a profile suggesting that the M(3) receptor subtype is essential i n the carbachol effect. Phospholipase C activity was estimated via mea surement of total production of inositol phosphates in cultured human trabecular meshwork cells pre-exposed to H-3-myoinositol. In these cel ls, carbachol also stimulated phosphoinositide production in a dose-de pendent manner, and an antagonist profile similar to that seen for cal cium response was obtained when carbachol was used as the effector. Th e data indicate that muscarinic effects on cultured human trabecular m eshwork calcium mobilization and phospholipase C activity are mediated by an M(3)-like receptor subtype. Therefore, the muscarinic M(3) rece ptor may play a role in trabecular meshwork cell function(s). (C) 1996 Academic Press Limited