Abstract 1244: CaMKII Contributes to Intracellular pH Recovery from an Acid Load via the Activation of the Na+/H+ Exchanger
Na+/H+ exchanger (NHE) activation plays a key role in pHi recovery from acid loads. This activation has been attributed to H+ and MAPK interactions with allosteric and regulatory domains, respectively. Recent evidence has linked the spontaneous mechanical recovery from acidosis with the activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII). However, the impact of this kinase on NHE activity and pHi recovery is not well defined. We tested the hypothesis that CaMKII activates NHE and contributes to pHi recovery from acidosis. For this purpose we subjected adult rat cardiac myocytes, loaded with the pHi indicator SNARF-1/AM, to intracellular acidosis generated by 1) NH4Cl pulse, followed by cero Na+ (persistent acidosis) and its washout (Fig 1A⇓, n=6) 2) Substitution of HEPES buffer with NaHCO3 buffer equilibrated with 5% CO2-95% O2 (Bic) at the same pHo (7.4) (Fig 1B⇓, n=5) 3) Hypercapnia at constant pHo induced by switching perfusate from a Bic solution to a similar one equilibrated with 20% CO2-80% O2 but with a higher [NaHCO3] to keep pHo constant at 7.4 (Fig 1C⇓, n=4). In all cases, the rate of pHi recovery (dpHi/dt), measured by epifluorescence, was used as an index of NHE activity. Regardless of the approach used, pretreatment with two structurally different CaMKII inhibitors KN-93 (1μM) or AIP (2.5 μM), significantly decreased the rate of pHi recovery from acidosis whereas pretreatment of cells with the inactive analog KN-92 did not affect pHi recovery. These results clearly demonstrate that CaMKII regulates NHE activity contributing to pHi recovery from acidosis. This mechanism could thus play an important role in the mechanical recovery from acidosis.