Inhibition of carbonic anhydrase prevents the Na+/H+ exchanger 1-dependent slow force response to rat myocardial stretch

VARGAS LA - DÍAZ RG; SWENSON ER; PÉREZ NG; ÁLVAREZ BV

AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY

AMER PHYSIOLOGICAL SOC

Lugar: Bethesda; Año: 2013 vol. 305 p. 228 - 237

0363-6135

Myocardial stretch is an established signal that leads to hypertrophy. Myocardial stretch inducesa first immediate force increase followed by a slow force response (SFR), which is aconsequence of an 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 itstransport activity. We aimed to test the role of CAII bound to NHE1 in the SFR. The SFR andchanges in intracellular pH (pHi) were evaluated in rat papillary muscle bathed with CO2/HCO3- buffer and stretched from 92% to 98% of the muscle maximal force development length for 10min, in the presence of the CA inhibitor 6-ethoxzolamide (ETZ, 100 μM). SFR control was120±3% (n=8) of the rapid initial phase and was fully blocked by ETZ, 99±4% (n=6). The SFRcorresponded with a maximal increase in pHi of 0.18±0.02 pH units (n=4), and pHi changes wereblocked by ETZ (0.04±0.04, n=6), as monitored by epifluorescence. NHE1/CAII physicalassociation was examined in the SFR by coimmunoprecipitation, using muscle lysates. CAIIimmunoprecipitated with an anti-NHE1 antibody and the CAII immunoprecipitated proteinlevels increased 58±9% (n=6) upon stretch of muscles, assessed by immunoblots. The p90RSKkinase inhibitor SL0101-1 (10 μM) blocked the SFR of heart muscles after stretch 102±2%(n=4), and reduced the binding of CAII to NHE1, suggesting that the stretch-inducedphosphorylation of NHE1 increases its binding to CAII. CAII/NHE1 interaction constitutes acomponent of the SFR to heart muscle stretch which potentiates NHE1-mediated H+ transport inthe myocardium.