The differences in gene expression among the fiber types of skeletal muscle have long fascinated scientists, but for the most part, previous experiments have only reported differences of one or two genes at a time. The evolving technology of global mRNA expression analysis was employed to determine the potential differential expression of approximately 3,000 mRNAs between the white quad (white muscle) and the red soleus muscle (mixed red muscle) of female ICR mice (30-35 g). Microarray analysis identified 49 mRNA sequences that were differentially expressed between white and mixed red skeletal muscle, including newly identified differential expressions between muscle types. For example, the current findings increase the number of known, differentially expressed mRNAs for transcription factors/coregulators by nine and signaling proteins by three. The expanding knowledge of the diversity of mRNA expression between white and mixed red muscle suggests that there could be quite a complex regulation of phenotype between muscles of different fiber types.

We studied the effects of regular diet (035% NaCl/1.1% potassium), high sodium diet (4% NaCl/0.75% potassium), or high sodium and high potassium diet (4% NaQ/2.11% potassium) on blood pressure, plasma renin activity, renal and cerebrovascular lesions, and incidence of stroke and mortality in male stroke-prone spontaneously hypertensive rats (SHRSP). In the first 4 weeks, the rise in blood pressure was higher hi high NaQ than in high NaCI/high potassium or regular diet groups. However, by 8 and 12 weeks, the blood pressure in all three groups was similar. After 4 weeks of diet, plasma renin activity was similar in the three groups (3.4±0.8, 4.1±0.9, and 52±1.6 ng/ml/hr, in high NaO, high NaCI/high potassium, and regular diet groups, respectively) and were not related to sodium excretion. After 8 weeks, plasma renin activity was significantly increased only in the high NaQ group (13.7±3.7 ng/ml/hr), and by 12 weeks plasma renin activity was significantly higher in the high NaCl group (253 ±3.6 ng/ml/hr) than in the high NaCI/high potassium (11.1±2.9 ng/ml/hr) or in the regular diet (7.8±4.6 ng/ml/hr) groups. Moderate to severe renal vascular lesions were first detected in the high NaQ group by 8 weeks of diet At 12 weeks, renal vascular damage index (RVDI), estimated hlstologically, was significantly higher in the high NaCl group (RVDI=79±14) than hi the high NaCI/high potassium (RVDI=40±ll) and regular diet (RVDI=7.8±4.6) groups. At this time, incidence of stroke was 81% in high NaCl, 24.5% in high NaCI/high potassium, and 7.7% in regular diet groups. Hie data demonstrate that: 1) the increase in mortality, stroke, and renal and cerebrovascular lesions in SHRSP fed a high sodium diet is associated with a paradoxical rise in plasma renin activity; 2) the protective effect of high potassium hi SHRSP fed a high potassium diet is related to a lower blood pressure at 2 -4 weeks and a lower plasma renin activity, but not a lower blood pressure at 8-12 weeks; 3) this rise in plasma renin activity demonstrates that a high potassium diet suppresses or delays a primary or secondary paradoxical rise hi plasma renin activity and thus, angiotensin JJ in the rats fed a high sodium diet This action together with possible direct effects of potassium hi the vasculature contributes to the protective effect on end organ damage and stroke hi SHRSP. {Hypertension 1990;15:318-326)