Force velocity relationships in vascular smooth muscle. The influence of temperature

Force velocity relationships of isolated vascular smooth muscle preparations were examined in the tetanized rat portal--anterior mesenteric vein by means of afterloaded isotonic contractions. Lowering of the temperature from 37 degrees C to 25 degrees C caused an average decrease of the follwoing parameters: maximal velocity of shortening at zero load from 0.51 to 0.28 muscle length/sec; maximal rate of tension increase (dT/dt) from 847 to 362 dyn/sec; mechanical tension developed at the maximum of dT/dt from 43 to 34% of the peak force generation; constant b of Hill's equation from 0.18 to 0.09 muscle length/sec. The latency was prolonged from 0.33 to 0.56 sec, and the time-to-maximum of dT/dt from 0.9 to 1.6 sec. Between 27 degrees C and 37 degrees C the following Q10 values were calculated: for the maximal velocity of shortening at zero load 1.56; for the maximal rate of tension increase 1.88; for the latency 1.63. No distinct influence of temperature could be observed on the extent of isotonic shortening at zero load (3.69 muscle length at 37 degrees C), on the extent of peak force generation (1107 dyn at 37 degrees C), and on constant a of Hill's equation (0.35 at 37 degrees C). It is concluded that parameters of contraction velocity in vascular smooth muscle depend on temperature, whereas the extent of contraction is independent of temperature. These findings are discussed in connection with the theory of the sliding-filament mechanism.