L-type Ca2+ channel 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 their recovery after support with LV assist devices (LVAD) were studied. L-type Ca2+ current (I-Ca,I-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 (MA) in nonfailing (NF), failing (F), and LVAD-supported human left ventricular myocytes (HVMs). Basal I-Ca,I-L density was not different in the 3 groups but I-Ca,I-L was activated at more negative voltages in F- and LVAD- versus NF-HVMs (V-0 5: -7.18+/-1.4 and -7.0 +/- 0.9 versus 0.46 +/- 1.1 mV). Both ISO and db-cAMP increased I-Ca,I-L in NF- and LVAD- significantly more than in F-HVMs (NF >LVAD> F: ISO: 90 +/- 15% versus 77 +/- 19% versus 24 +/- 12%; db-cAMP: 235%>172%>90%). ISO caused a significant leftward shift of the I-Ca,I-L activation curve in NF- and LVAD- but not in F-HVMs. After ISO and db-cAMP, the I-Ca,I-L activation was not significantly different between groups. BayK also increased I-Ca,I-L more in NF-(81 +/- 30%) and LVAD- (70 +/- 15 %) than in F- (51 +/- 8%) HVMs. OA increased I-Ca,I-L by 85.6% in NF-HVMs but had no effect in F-HVMs, while PP2A decreased I-Ca,I-L in F-HVMs by 35% but had no effect in NF-HVMs. These results suggest that the density of LTCC is reduced in F-HVMs but basal I-Ca,I-L density is maintained by increasing in LTCC phosphorylation.