L-type calcium channel biophysical properties, density and regulation are altered in failing human ventricular myocytes and recover after support with mechanical assist devices

Ca2+ influx through the L-type calcium channel (LTCC) induces Ca2+ release from the sarcoplasmic reticulum (SR) and maintains SR Ca2+ loading. Alterations in LTCC properties, their contribution to the blunted adrenergic responsiveness in failing hearts and the additional changes after support with LV assist devices (LVAD) were studied. L-type Ca2+ current (I_Ca-L) was measured under basal conditions and in the presence of isoproterenol (ISO), dibutyryl-cAMP (db-cAMP), Bay K 8644 (BayK), okadaic acid (OA, a phosphatase inhibitor) and phosphatase 2A (PP2A) in nonfailing (NF), failing (F) and LVAD supported human left ventricular myocytes (HLVMs) with whole-cell voltage-clamp technique. Basal I_Ca-L density was not different in the three groups but V _0.5(d∞), the voltage at which half of I_Ca-L is activated, was more negative in F- vs. NF-HLVMs. Further studies this negative V _0.5(d∞) was more prominent in HLVMs from ischemic hearts vs. from idiopathic hearts.; ISO, db-cAMP and BayK increased I_Ca-L in NF- significantly more than in F-HLVMs. Both ISO and BayK caused a significant leftward shift of the I_Ca-L activation curve in NF- but not in F-HLVMs. After ISO, db-cAMP and BayK, the I_Ca-L activation was not significantly different between groups but I_Ca-L density is lower in F-HLVMs than in NF-HLVMs. OA increased I_Ca-L by 85.6% in NF-HLVMs but had no effect in F-HLVMs, while PP2A decreased I_Ca-L in F-HLVMs by 35% but had no effect in NF-HLVMs. In NF-HLVMs pretreated with ISO or db-cAMP, BayK had diminished effect on I_Ca-L and did not significantly change V_0.5(d∞) in ISO or db-cAMP pretreated NF-HLVMs. Conversely I_Ca-L in NF-HLVMs pretreated with BayK, I_Ca-L lost response to ISO.; The defects of the LTCC and its regulation in F-HLVMs could be partially recovered by supporting failing hearts with LVAD. Although V_0.5(d∞) remained at negative potential, the responses of I_Ca-L to ISO, db-cAMP and BayK were reversed to the extent near normal.; In conclusion, the density of LTCC is reduced in F-HLVMs but basal I _Ca-L density is maintained by increasing LTCC phosphorylation. These abnormalities in the LTCC contribute to reduced β-adrenergic effect in F-HLVMs. These defects in the LTCC and its regulation are partially recovered in LVAD-LVMs.