Role of the phosphorylation of Thr17 residue of phospholamban on the mechanical recovery during acidosis

FERRERO P,; MUNDIÑA-WEILENMANN C,; SAID M,; VITTONE L,; KRANIAS EG,; MATTIAZZI A

Iguazú, Argentina,

Congreso; XIII Meeting of the Latin American Section of the ISHR; 2004

Latin American Section of the ISHR

We studied the time course of phospholamban phosphorylation and its functional impact on the mechanical recovery during acidosis in Langendorff-perfused rat hearts. Mechanical recovery had two phases: a rapid, early one (3 min) and a slow, late one. During the early phase, contractility and relaxation recovered 67 ± 9% and 77 ± 11%, respectively, in association with a transient (3 min) increase in CaMKIIdependent Thr17-phospholamban phosphorylation (ThrP) from 36 ± 5% to 58 ± 7% (expressed as % of maximal isoproterenol ThrP, n = 12-21); 1 or 5 ìM of the CaMKIIinhibitor KN-93, decreased ThrP to basal levels and similarly impaired the early relaxation recovery (50%). In spite of the similar decrease in ThrP, only 5 ìM KN-93 significantly inhibited the early contractile recovery (5 ± 1%, n = 14) and blunted the late mechanical recovery. Inhibition of Na+/H+ exchanger (NHE) by cariporide did not modify either ThrP (60 ± 5%, n = 9) or the early relaxation recovery, but abolished the late relaxation recovery and the whole contractile recovery. Inhibition of the reverse mode of Na+/Ca2+ exchanger (NCX) by KB-R7943 significantly decreased ThrP to 38 ± 5% (n = 7) but accelerated the early contractile recovery (124 ± 52% at 1 min). KB-R7943 plus cariporide decreased ThrP to 44 ± 6% (n = 7) and prevented the whole mechanical recovery. The results indicated that: (1) ThrP is linked to the reverse NCX mode, but not to NHE, being responsible for 50% of the early relaxation recovery; (2) in the absence of ThrP, NHE is necessary for the early relaxation recovery; (3) the reverse NCX mode has a negative effect, that opposes to the early contractile recovery and (4) the early contractile recovery and the whole late mechanical recovery are dependent on CaMKII and NHE but independent of ThrP.