Effects of hypokalemia on cardiac growth

In neonatal myocytes grown in culture, reductions in extracellular potassiu m concentration produced a hypertrophic response as assessed by induction o f early response genes, atrial natriuretic peptide and skeletal actin, and repression of the alpha 3 isoform of the sodium pump in a dose dependent ma nner. The degree of alpha 3 repression appeared to be dose dependent with d ecreases in media (K). Similarly, decreases in media potassium concentratio ns caused increases in cytosolic calcium concentration in a dose dependent manner; moreover these increases in cytosolic calcium concentration correla ted quite well with repression of alpha 3 expression. In contrast, although moderate reductions of potassium concentration induced upregulation of skA CT and ANP, severely reduced potassium concentrations caused repression of skACT and ANP expression. In parallel studies performed in vivo, 3-5 weeks dietary K restriction indu ced molecular phenotypical changes similar to that seen in the neonatal myo cyte model without demonstrable growth as assessed by the heart weight/body weight ratio. However, when rates subjected to dietary K restriction were subsequently subjected to acute aortic constriction, cardiac growth was gre ater than in rats fed a control diet. These data suggest that hypokalemia may produce molecular phenotypic altera tions consistent with cardiac hypertrophy as well as contribute to hypertro phy in an in vivo model.