INVESTIGADORES
PEREZ Nestor Gustavo
congresos y reuniones científicas
Título:
Inhibition of carbonic anhidrase prevents the Na+/H+ exchanger-1 dependent slow force response to rat myocardial stretch
Autor/es:
VARGAS LA; DÍAZ RG; PÉREZ NG; ÁLVAREZ BV
Lugar:
Gramado, Río Grande do Sul
Reunión:
Congreso; XLVII Congresso Anual da Sociedade Brasileira de Fisiologia; 2012
Resumen:
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.