Sensitive force transducer system for mechanical studies of single isolated vascular smooth muscle cells.

Abstract

To measure forces of the order of 0·1 μN, generated by single isolated vascular smooth muscle cells, a sensitive transducer system has been developed. A video displacement detection system and an inductive position detector were used to control the tip displacement of a glass microneedle. The bending of the microneedle was used as a measure of the force generated by a single smooth muscle cell attached to the tip. During isometric contractions the stiffness of the system was 0·7 μN μm−1. A signal limiter in one of the feedback loops made it possible to reduce the stiffness of the system to 4 nN μm−1 when an adjustable force limit was exceeded. These two conditions of the system made it possible to measure both isometric and isotonic contractions of a single muscle cell. The force limiter may also be used to protect the preparation against excessive forces developed during contraction. A mechanical model of the system and the vascular smooth muscle cell was simulated and verified. The parameters of the model for a single vascular smooth muscle cell, two viscoelastic springs in parallel, could be estimated from the measurements. The bandwidth of the system during isometric contraction was 17 Hz.