Initially during acidosis, Ca transient amplitude (Δ[Ca] i) and the rate constant of [Ca]i decline (k Ca) are decreased, but later during acidosis Δ[Ca]i and kCa partially recover. This recovery in rat myocytes could be inhibited by KN-93 suggesting that CaMKII-dependent protein phosphorylation (and enhanced SR Ca uptake) may be responsible. To test whether phospholamban (PLB) is required for the Δ[Ca]i and kCa recovery during acidosis, we used isolated myocytes from PLB knockout (PLB-KO) vs. wild-type (WT) mice. [Ca]i was measured using fluo-3. During the initial phase of acidosis (1-4 min), Δ[Ca]i decreased in WT myocytes (n = 8) from 1.75 ± 0.19 to 1.10 ± 0.13 ΔF/F 0 (P < 0.05) and kCa decreased from 3.20 ± 0.22 to 2.38 ± 0.18 s-1 (P < 0.05). Later during acidosis (6-12 min), Δ[Ca]i partially recovered to 1.41 ± 0.18 ΔF/F0 and kCa to 2.78 ± 0.22 s-1 (i.e. both recovered by ∼50%). CaMKII inhibition using KN-93 completely prevented this recovery of Δ[Ca]i and kCa during late acidosis in WT myocytes. In PLB-KO myocytes (n = 11) Δ[Ca] i decreased during early acidosis from 2.92 ± 0.31 to 1.33 ± 0.17 ΔF/F0 (P < 0.05) and kCa decreased from 10.45 ± 0.56 to 7.58 ± 0.68 s-1 (P < 0.05). However, Δ[Ca]i did not recover during late acidosis and k Ca decreased even more (6.59 ± 0.65 s-1). Parallel results were seen for contractile parameters. We conclude that PLB is crucial to the recovery of Δ[Ca]i and kCa during acidosis. Moreover, PLB phosphorylation by CaMKII plays an important role in limiting the decline in Ca transients (and contraction) during acidosis.
- Protein phosphatases
ASJC Scopus subject areas
- Molecular Biology
- Cardiology and Cardiovascular Medicine