TROPONIN-I PHOSPHORYLATION DOES NOT INCREASE THE RATE OF RELAXATION FOLLOWING LASER FLASH-PHOTOLYSIS OF DIAZO-2 IN GUINEA-PIG SKINNED TRABECULAE

In vivo, two effects of beta-adrenergic stimulation in cardiac muscle are phosphorylation of troponin I and an increase in relaxation rate. In vitro, cardiac TnI can be phosphorylated by protein kinase A (PKA). We have used the technique of laser flash photolysis of the calcium c helator diazo-2 to investigate the effect of phosphorylation of TnI on the relaxation rate of skinned trabeculae from the guinea-pig at 12 d egrees C. The fibres were phosphorylated by PKA, and double exponentia l curve fits of the average relaxation transients showed no significan t difference between the rate constants of the phosphorylated and cont rol cases. We conclude that TnI phosphorylation has no effect on the r ate of relaxation in skinned trabeculae from the guinea-pig following diazo-2 photolysis.