DIFFERENTIAL-EFFECTS OF NOVEL PROTAMINE VARIANTS ON MYOCYTE CONTRACTILE FUNCTION WITH LEFT-VENTRICULAR FAILURE

Background. Protamine administration can cause left ventricular (LV) d ysfunction, which may have clinical significance in the setting of con gestive heart failure (CHF). Protamine variants have recently been con structed with heparin reversal capacity similar to protamine. The purp ose of this study was to examine the potential differential effects of these protamine variants on isolated myocyte contractile function in normal myocytes and in myocytes after the development of CHF. Methods. Contractile function was measured by means of computer-aided videomic roscopy in myocytes from five normal pigs and five pigs with CHF induc ed by rapid pacing (240 beats/min for 3 weeks). Myocyte contractility was examined in the presence of 40 mu g/ml native protamine or one of three protamine variants: (I) reduced charge (+18) and lysine substitu ted for arginine; (2) lysine-substituted variant with glutamic acid su bstituted for the initial proline; or (3) arginine-rich peptide with a terminal arginine-glycine-aspartic acid (RGD) amino acid sequence. Re sults. In the presence of native protamine, myocyte percent shortening fell from baseline in both the normal (2.86 +/- 0.15 versus 4.58 +/- 0.08, p < 0.05) and the CHF groups (1.01 +/- 0.06 versus 2.07 +/- 0.05 , p < 0.05). With both of the lysine-substituted protamine variants, p ercent shortening fell from baseline in the normal group (3.42 +/- 0.2 0 for arginine and 3.74 +/- 0.20 for glutamic acid versus 4.58 +/- 0.0 8, p < 0.05), and was unchanged in the CHF group (1.94 +/- 0.13 versus 2.07 +/- 0.05, P = 0.34 for arginine; and 1.96 +/- 0.10 versus 2.07 /- 0.05, p = 0.31, for glutamic acid). However, with the arginine/RGD variant, percent shortening fell from baseline in both the normal (2.8 6 +/- 0.23 versus 4.58 +/- 0.08, p < 0.05) and the CHF groups (1.32 +/ - 0.10 versus 2.07 +/- 0.05, p < 0.05). Conclusions. Specific changes in the primary and secondary structures of protamine had different eff ects on myocyte contractile function. Furthermore, the negative effect s of lysine-substituted protamine variants on myocyte contractility we re less pronounced in both CHF and normal myocytes. Thus protamine var iants may be of clinical use, particularly in the setting of preexisti ng LV dysfunction.