A low voltage activated Ca(2+) current found in a subset of human ventricular myocytes

Low voltage activated (I(Ca-LVA)) calcium currents including Cav1.3 and T-type calcium current (I(Ca-T)) have not been reported in adult human left ventricular myocytes (HLVMs). We tried to examine their existence and possible correlation with etiology and patient characteristics in a big number of human LVMs isolated from explanted terminally failing (F) hearts, failing hearts with left ventricular assist device (F-LVAD) and nonfailing (NF) human hearts. LVA (I(Ca-LVA)) was determined by subtracting L-type Ca(2+) current (I(Ca-L)) recorded with the holding potential of −50 mV from total Ca(2+) current recorded with the holding potential of −90 mV or −70 mV. I(Ca- LVA) was further tested with its sensitivity to 100 µM CdCl(2) and tetrodotoxin. Three HLVMs (3 of 137 FHLVMs) from 2 (N = 30 hearts) failing human hearts, of which one was idiopathic and the other was due to primary pulmonary hypertension, were found with I(Ca-LVA). I(Ca-LVA) in one FHLVM was not sensitive to 100 µM CdCl(2) while I(Ca-LVA) in another two FHLVMs was not sensitive to tetrodotoxin. It peaked at the voltage of −40~-20 mV and had a time-dependent decay faster than I(Ca-L) but slower than sodium current (I(Na)). I(Ca-LVA) was not found in any HLVMs from NF (75 HLVMs from 17 hearts) or F-LVAD hearts (82 HLVMs from 18 hearts) but a statistically significant correlation could not be established. In conclusion, I(Ca-LVA) was detected in some HLVMs of a small portion of human hearts that happened to be nonischemic failing hearts.