A low voltage activated Ca2+current found in a subset of human ventricular myocytes

Low voltage activated (ICa-LVA) calcium currents including Cav1.3 and T-type calcium current (ICa-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 (ICa-LVA) was determined by subtracting L-type Ca(2+)current (ICa-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 mu M 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 ICa-LVA. I(Ca-LVA)in one FHLVM was not sensitive to 100 mu M CdCl(2)while I(Ca-LVA)in another two FHLVMs was not sensitive to tetrodotoxin. It peaked at the voltage of -40 similar to-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.