Measurements of the cross-bridge attachment/detachment process within intact sarcomeres by surface plasmon resonance

We have developed a surface plasmon resonance (SPR) system to monitor the c ross-bridge attachment/detachment process within intact sarcomeres from mou se heart muscle. SPR occurs when laser light energy is transferred to surfa ce plasmons that are resonantly excited in a metal (gold) film. This resona nce manifests itself as a minimum in the reflection of the incident laser l ight and occurs at a characteristic angle. The angle of the SPR occurrence depends on the dielectric permittivity of the sample medium adjacent to the gold film. Purified sarcomeric preparations are immobilized onto the gold film in the presence of a relaxing solution. Replacement of the relaxing so lution with increasing Ca2+ concentration solution activates the cross-brid ge interaction and produces an increase in the SPR angle. These results imp ly that the interaction of myosin heads with actin within an intact sarcome re changes the dielectric permittivity of the sarcomeric structure. In addi tion, we further verify that SPR measurements can detect the changes in the population of the attached cross-bridges with altered concentrations of ph osphate, 2,3-butanedione monoxime, or adenosine triphosphate at a fixed cal cium concentration, which have been shown to reduce the force and increase the cross-bridge population in attached state. Thus, our data provide the f irst evidence that the SPR technique allows the monitoring of the cross-bri dge attachment/detachment process within intact sarcomeres.