Effects of ionic strength on force transients induced by flash photolysis of caged ATP in covalently crosslinked rabbit psoas muscle fibers.

Single fibers from glycerinated rabbit psoas muscle were treated with 1-ethyl-3[3-(dimethylamino) propyl] carbodiimide (EDC), after rigor was induced, to crosslink myosin heads to actin. The optimally pre-stretched (approximately 1.8%), partially crosslinked fibers produce a large force when MgATP is depleted, and this force is abolished when MgATP is reintroduced, even in high ionic strength solution of 0.5 M (Tawada et al. 1989). We investigated the rate of force decay in the crosslinked, force-producing fibers using pulse photolysis of caged ATP (Goldman et al. 1984). The decay of force was fast, the rate of which depending both on the ionic strength and on the amount of ATP released (0.2-2.2 mM) with the second-order rate constant of 0.5-1 x 10(5) M-1s-1 at the ionic strength of 0.5 M. At high ionic strength (1-2M) force decayed at lower rate. At low ionic strength (0.1-0.2 M), however, force decayed more rapidly, but force redeveloped subsequently, which is probably caused by uncrosslinked myosin heads.