Differential smooth muscle-like contractile properties of trabecular meshwork and ciliary muscle

Abstract

The contractile properties of bovine trabecular meshwork and ciliary muscle strips were investigated using an electromagnetic force-length transducer for isometric force measurements. Acetylcholine, pilocarpine and aceclidine administration resulted in dose-dependent contractions of trabecular meshwork and ciliary muscle. Absolute forces were approximately 10 times larger in ciliary muscle than in trabecular meshwork. Maximal force evoked by aceclidine (5 × 10 −5 m), when compared to the pilocarpine (5 × 10 −5 m) response, was significantly higher in trabecular meshwork than in ciliary muscle. The results were 172·5 ± 12·6% ( n = 7) and 138·9±4·0% ( n = 8, P < 0·05), respectively. Depolarization induced by raised external potassium (120 m m), when compared to the acetylcholine response (10 −3 m), resulted in a small contraction of 19·3±4·2% in trabecular meshwork ( n = 5), and of 59·0±13·7% in ciliary muscle ( n = 4, P < 0·01). Both responses were inhibited by atropine (10 −5 m). The differential potassium effect may be explained by the large number of cholinergic nerve endings in ciliary muscle as compared to trabecular meshwork tissue. Recently, a dissociation between the effects of aceclidine on outflow resistance and accommodation has been described. Our data are consistent with these observations and provide evidence for a direct role of trabecular meshwork contractility in aqueous outflow regulation.