Reactivation of contraction in detergent-lysed teleost retinal cones.

Abstract

Teleost retinal cones contract in the light and elongate in the dark. In the green sunfish, L. cyanellus, the necklike myoid region of the cone contracts from as much as 120 .mu.m (midnight dark-adapted) to 6 .mu.m in the fully light-adapted state. When dark-adapted fish are exposed to light (1.4 lux), cone myoids contract with a linear rate of 1.5 .+-. 0.1 .mu.m/min. Detergent-lysed motile models of teleost retinal cones exhibit Ca and ATP-dependent reactivated contraction, with morphology and rate comparable to that observed in vivo. For reactivation studies isolated dark-adapted retinas were lysed with nonionic detergent Brij-58 (0.1-1.0%). In reactivation medium containing 10-5 M free Ca and 4 mM ATP, the lysed cones contracted with normal morphology at in vivo rates (1.4 .+-. 1 .mu.m/min). Little contraction was observed if ATP or detergent was deleted from the medium or if free Ca levels were < 10-8 M. Ultrastructural examination of cone models lysed with 1% Brij-58 revealed that, in spite of extensive extraction of the cytoplasmic matrix, cytoskeletal components (thin filaments, intermediate filaments and microtubules) were still present. Extensively extracted motile models of teleost retinal cones were produced which undergo Ca- and ATP-dependent reactivated contraction with normal morphology at physiological rate.