Chronic hypertension changes myosin isoenzyme pattern and decreases myosin phosphorylation in the rat heart

We investigated systolic blood pressure (BP), ventricular myosin isoenzyme (MI) pattern, and myosin P-light chain phosphorylation (MP) of male and female normotensive (WKY) and spontaneously hypertensive rats (SHRSP). BP increased in SHRSP of both sexes during maturation. Male SHRSP reached a significantly higher BP (262 mmHg at week 64) than female SHRSP (217 mmHg at week 64). WKY remained at approximately 114 mmHg throughout the life-span investigated (5 to 64 weeks). MI pattern (expressed as %V1/%V3) shifted age-dependent to the V3 form: In female SHRSP MI pattern was 41/25 at week 18, 34/35 and 40/38 within week 22 to 32, and shifted to 18/53 until week 64. In male SHRSP MI pattern was 25/44 at week 18 and shifted gradually to 13/60 until week 53. MI patterns of WKY of both sexes were 100% V1 within week 5 to 12, shifted gradually to 51/23 and then remained constant until week 64. MP of the ventricle of female WKY and SHRSP was approximately 41% until week 52. At week 64, however, MP of female SHRSP decreased to 18% whereas female WKY remained at approximately 41%. MP of the ventricle of male WKY and SHRSP was approximately 38% until week 38. At week 44, however, MP of male SHRSP decreased to 22% whereas male WKY remained constant. Isometric tension generation of chemically skinned rat ventricular fibres increased after MP by calcium-calmodulin-dependent myosin light chain kinase. Both the shift to the V3 form and the decreased MP level might contribute to the development of cardiac failure in old SHRSP of both sexes.