Na+-H+ exchanger (NHE-1)-mediated recovery from acidosis is enhanced by Ca2+/calmodulin protein kinase II (CaMKII) which phosphorylates the exchanger at noncanonical sites

LEZCANO N; VILA-PETROFF M; MUNDIÑA - WEILENMANN C; SNABAITIS AK; AVKIRAN M; MATTIAZZI A

Buenos Aires

Congreso; XVII Meeting ISHR Latin American Section. XXVII Congreso Nacional de Cardiología; 2009

ISHR Latin American Section - Federación Argentina de Cardiología

Na+/H+ exchanger type 1 (NHE-1), the main pHi controlling transporter activated during acidosis in the myocardium, is in vitro phosphorylated by CaMKII. Furthermore acidosis-induced activation of CaMKII is known to have important implications in the mechanical recovery from an acid load. To assess the putative role of CaMKII in the regulation of NHE-1 activity during intracellular acidosis, adult rat isolated myocytes loaded with the pHi indicator SNARF-1/AM were subjected to an NH4Cl pulse in the absence and presence of CaMKII inhibition. Both CaMKII inhibitors, KN-93 (1 ìM) or the more specific AIP (1 ìM) slowed the rate of pHi recovery after the acid load. The modulatory role of CaMKII on NHE-1 activity was further confirmed in myocytes overexpressing CaMKII: a faster pHi recovery from intracellular acidosis was observed in CaMKII-overexpressing myocytes when compared to âgal-overexpressing myocytes (dpHi/dt: 0.195±0.04 vs. 0.045± 0.010 min−1, n=8, respectively). In vitro studies with fusion proteins containing wild-type or mutated (Ser/Ala) versions of the C terminal domain of NHE-1 indicated that CaMKII phosphorylates NHE-1 at residues other than the canonical phosphorylation sites (Ser648, Ser703 and Ser796). The results indicate a significant role of CaMKII in the stimulation of sarcolemmal NHE-1 activity in response to intracellular acidosis.