Meeting Abstract
When a muscle has been stretched during activation, the passive tension of the relaxed muscle is greater than after an isometric contraction at the stretched length. This muscle property is not well understood, but the protein titin has been suggested to play a role. To study titin’s contribution to passive tension along the length-tension curve, we used mdm mutant mice, which carry a deletion in the N2A region of their titin gene. This deletion makes mdm muscles passively stiffer, but actively more compliant, than wild type muscle. Using the mdm mouse genotypes, we asked how passive tension changes with activation and stretch along the length tension curve, and whether it varies among genotypes? We used soleus muscles from mdm genotypes to perform three tests using a servomotor force lever: a reference isometric contraction, a 5% passive stretch, and an activation+5% stretch. These muscle tests were performed from Lo-5% to Lo+20% in 5% increments. We then compared the effect of stretch versus activation+stretch on muscle passive tension. In both wild type and mutant muscle, activation alone caused a slight depression in passive tension. In contrast, both passive stretch and activation+stretch increased passive tension. In wild type muscles, activation+stretch increased passive tension more than stretch alone at lengths greater than Lo+5%. In mutant muscle, passive stretch alone generally increased passive tension more than stretch+activation. The results suggest that a structural element (i.e. titin) becomes stiffer when activated and/or stretched, and that wild type titin is affected more by activation than mdm mutant titin. Supported by NSF IOS-1025806.
