Organ hypertrophic signaling within caveolae membrane subdomains triggered by ouabain and antagonized by PST 2238

In addition to inhibition of the Na-K ATPase, ouabain activates a signal transduction function, triggering growth and proliferation of cultured cells even at nanomolar concentrations. An isomer of ouabain ( EO) circulates in mammalians at subnanomolar concentrations, and increased levels are associated with cardiac hypertrophy and hypertension. We present here a study of cardiac and renal hypertrophy induced by ouabain infused into rats for prolonged periods and relate this effect to the recently described ouabain-induced activation of the Src-EGFr-ERK signaling pathway. Ouabain infusion into rats ( 15 mu\g/kg/day for 18 weeks) doubled plasma ouabain levels from 0.3 to 0.7 nM and increased blood pressure by 20 mm Hg ( p < 0.001), cardiac left ventricle ( + 11%, p < 0.05), and kidney weight ( + 9%, p < 0.01). These effects in vivo are associated with a significant enrichment of alpha 1, beta 1, gamma a Na-K ATPase subunits together with Src and EGFr in isolated renal caveolae membranes and activation of ERK1/2. In caveolae, direct Na-K ATPase/Src interactions can be demonstrated by co-immunoprecipitation. The interaction is amplified by ouabain, at a high affinity binding site, detectable in caveolae but not in total rat renal membranes. The high affinity site for ouabain is associated with Src-dependent tyrosine phosphorylation of rat alpha 1 Na-K ATPase. The antihypertensive compound, PST 2238, antagonized all ouabain-induced effects at 10 mu g/kg/day in vivo or 10(-10) 10(-8) M in vitro. These findings provide a molecular mechanism for the in vivo pro-hypertrophic and hypertensinogenic activity of ouabain, or by analogy those of EO in humans. They also explain the pharmacological basis for PST 2238 treatment.