Effects of Temperature

The effect of temperature on the force-sarcomere velocity relation (200, 250, and 300 C) and maximum velocity of sarcomere shortening (V0; range 15°-35° C) was studied in trabeculae from rat heart. Sarcomere length and V. were measured by laser diffraction techniques. Sarcomere length and sarcomere velocity, determined from each of the first-order diffraction lines, differed by less than 4%. Slack sarcomere length in the trabeculae appeared to be 1.9 ,um. Isovelocity release techniques were used to obtain sarcomere velocity and VO directly. Sarcomere velocity was measured at SL=1.9-2.0 ,um for elimination of contributions of parallel elastic force and restoring force to the external load of the sarcomeres. Peak twitch force development (F.) was maximal (Fo.max) at 250 C at [Ca2'I0= 1.5 mM. Lowering of the temperature below 250 C led to development of spontaneous sarcomere activity and depression of F.; both responses could be prevented by the addition of 0.5 mM procaine. Increase of temperature above 250 C reduced twitch duration and F.. Hill's rectangular hyperbola fitted the force-velocity data if the load during shortening was less than 70% of F0. V. appeared to be independent of the level of activation at all temperatures when F0 was maintained above 90% of Fo.max, either by an increase of [Ca2']I (to 3.0 mM) or by paired pulse stimulation. V. increased with increasing temperature; the parameter a, calculated from force-velocity relations measured at 200, 250, and 300 C, decreased with increasing temperature. The Arrhenius plot of V0 was studied in detail over a wider temperature range (15°-35° C) and in smaller temperature increments. The relation was linear between 180 and 330 C; the observed Qlo, defined as the ratio of V0 measured at temperature (T) over VO at T100 C, was 4.6. A Q1o of 4.6 for V0 is consistent with the reported temperature dependence of rat cardiac actin-activated myosin ATPase, which suggests that the same reaction step may limit the activity of the enzyme in vitro and during shortening of the cardiac sarcomeres at zero external load.(Circulation Research 1990;66:1239-1254)