CENTRO DE INVESTIGACIONES CARDIOVASCULARES "DR. HORACIO EUGENIO CINGOLANI"
Unidad Ejecutora - UE
congresos y reuniones científicas
Inhibition of carbonic anhidrase prevents the Na+/H+ exchanger-1 dependent slow force response to rat myocardial stretch
VARGAS LA; DÍAZ RG; PÉREZ NG; ÁLVAREZ BV
Gramado, Río Grande do Sul
Congreso; XLVII Congresso Anual da Sociedade Brasileira de Fisiologia; 2012
Objective: Myocardial stretch is an established signal that leads to hypertrophy. The stretch of the cardiac muscle induces a biphasic force response consisting of a first immediate increase followed by a slow force response (SFR), which is a consequence of increased Ca²+ transient that follows the NHE1 Na+/H+ exchanger activation. Carbonic anhydrase II (CAII) binds to the extreme C-terminus of NHE1 and regulates its transport activity, forming an special transport metabolon system. We aimed to test the role of CAII bound to NHE1 in the SFR. Methodology: The SFR and changes in intracellular pH (pHi) were evaluated in rat papillary muscle stretched from 92% to 98% of the muscle maximal isometric length for 10 min, in the absence or presence of the CA inhibitor 6-ethoxyzolamide (ETZ, 100 uM). pHi changes in rat papillary muscles were monitored by fluorescent measurements of BCECF-AM. NHE1/CAII physical association was examined in the SFR by coimmunoprecipitation using rat papillary lysates. Results: SFR was 116±2% (n=8) of the rapid initial phase and was fully cancelled by ETZ, 99±4% (n=6), in the presence of bicarbonate (HCO3-). Under nominally HCO3- free conditions, the SFR corresponded with a maximal increase in pHi of 0.24±0.05 pH units (n=4) indicating activation of NHE1, and pHi changes were blocked by ETZ (0.05±0.06, n=6), monitored by fluorescent measurements of BCECF-AM. NHE1/CAII physical association examined in the SFR by coimmunoprecipitation showed that CAII immunoprecipitated with anti-NHE1 antibody and the CAII immunoprecipitated protein levels increased 58±9% (n=6) upon stretch of muscles, assessed by immunoblots. Earlier observations showed that ERK stimulates NHE1 activity, and that serum stimulates CAII binding to NHE1. Herein, the specific p90 ribosomal S6 kinase (p90RSK) inhibitor SL0101-1 (10 uM) blocked the SFR of heart muscles after 10 min stretch 102±2% (n=4), and reduced the binding of CAII to NHE1, indicating that the stretch-induced phosphorylation of NHE1 increases its binding to CAII. Conclusions: CAII/NHE1 interaction constitutes a component of the SFR to myocardial stretch which potentiates NHE1-mediated H+ transport in the heart. CAII induction is a prognostic molecular marker of the muscle stretch that precedes cardiac hypertrophy and CA inhibition may be an effective treatment for early pathologic cardiac growth.