Receptor‐responses in fresh human ciliary muscle

Abstract

1 The physiological and pharmacological properties of ciliary muscle isolated from fresh human eyes were investigated. 2 The muscle exhibited no spontaneous activity. Concentration-dependent contractions in response to carbachol were competitively antagonized by atropine (pA₂ = 8.95). 3 The muscle, precontracted by carbachol (2.7 × 10⁻⁴ M), responded to the application of isoprenaline by concentration-dependent relaxation blocked by propranolol (3.5 × 10⁻⁹ M to 3.5 × 10⁻⁸ M; pA₂ = 9.15). 4 Angiotensin-evoked contractions were antagonized by 8-Ala-angiotensin II (4.5 × 10⁻⁸ M) in a competitive manner, but were not inhibited by phentolamine or propranolol. 5 Contractions generated by electrical stimulation of the muscle (30 ms, 20 Hz, 60 pulses) were antagonized by atropine (10⁻⁷ M) and tetrodotoxin (6.3 × 10⁻⁷ M). Phentolamine and propranolol did not influence these responses. 6 An increase of the external potassium concentration ([K⁺]_o) from 5.4 to 158.8 mM produced a mechanical response, antagonized by atropine, but not influenced by tetrodotoxin, phentolamine or propranolol. 7 The human ciliary muscle appears to carry muscarinic and angiotensin receptors and β₂-adrenoceptors. The estimate of K_atropine for muscarinic receptors mediating carbachol-induced contractions agrees with estimates of K_atropine reported for human and rabbit iris.