Introduction

Abstract

Each of the following contributions, in some sense, concern the nature of unstimulated muscle, that is, the properties of relaxed myofibrils. The first report describes efforts to probe for attached cross-bridges in relaxed skinned fibers using very high speed stretches -- complete in about 150 μsec. The second paper describes an important new class of fibrous myofibrillar proteins. These very high molecular weight proteins (VHMWP) still remain in myofibrils extracted of most myosin and actin. This makes them good candidates as components of the additional sarcomere structures proposed in the third article. In that paper, mechanical and structural responses to stretching and swelling forces are described which can not be understood in terms of the present-day sliding filament model for the sarcomere. The authors offer a new model for striated muscle which incorporates three additional structures.