Figure 2.

Thin filaments remain motile but lose Ca²⁺-regulation at high temperature. (a) Time course of temperature (gray line; right ordinate) and sliding speed (solid squares, red fill; left ordinate) for regulated thin filaments (F-actin plus rhcTn and α-Tm) at pCa 9 during the heating phase of five cycles of heating and cooling. Points represent the mean sliding speed for 3–5 filaments during 1 s. At pCa 9, nonzero sliding speeds in heating cycles 3–5 indicate loss of Ca²⁺-regulation (dysregulation); note that temperature-dependent loss of Ca²⁺-regulation is fully reversible following cooling (beginning of cycles 4-5). (b) Data from (a) (pCa 9; solid squares, red fill) were replotted to eliminate time. Additional data for regulated thin filaments (F-actin plus rhcTn and α-Tm) at pCa 5 (⬤) and unregulated F-actin (▵) from the same series of experiments are also shown for comparison.