Ultrastructure and contractures of the pigeon iris striated muscle

Abstract
1. The ultrastructure of adult pigeon iris muscle fibres has been described with emphasis on the distribution of the sarcoplasmic reticulum (SR). Contractures due to superfusion with solutions of different [K+] (3-150 mM) and acetylcholine (ACh) and their modification by alteration of external [Ca2+] and [Mg2+] were studied in isolated pigeon iris.