Th. Cheng et al., COMPARISON OF CALCIUM-CURRENT IN ISOLATED ATRIAL MYOCYTES FROM FAILING AND NONFAILING HUMAN HEARTS, Molecular and cellular biochemistry, 157(1-2), 1996, pp. 157-162
To identify possible alterations of the L-type calcium currents (I-Ca,
I-L) in cardiomyopathy, I-Ca,I-L were recorded in atrial myocytes diss
ociated from the nonfailing heart (NF) of patients undergoing correcti
ve open-heart surgery and explanted failing heart (FH) of patients wit
h dilated cardiomyopathy undergoing heart transplantation. The patch-c
lamp technique was applied in the single-electrode whole-cell mode. Th
e electrophysiological properties of I-Ca,I-L, including cell capacita
nce and current density, were similar in atrial myocytes from both gro
ups of patients. Further to identify possible alterations of the myoca
rdial beta-adrenergic pathway in cardiomyopathy, we examined the effec
ts of isoproterenol, forskolin, 8-Br-cAMP and IBMX on I-Ca,I-L in both
groups of atrial myocytes. Perfusion of isoproterenol (1 mu M) signif
icantly increased the peak I-Ca,I-L by 51.5+/-44% in 6 atrial myocytes
from NF but increased only by 135+/-25% in 27 atrial myocytes from FH
. However, forskolin (1 mu M) or 8-Br-cAMP (0.1 mM) increased the peak
I-Ca,I-L to a similar extent in atrial myocytes from NF and FH. IBMX
(20 mu M) also induced a comparable increase in the peak I-Ca,I-L by 2
13+/-31% (n=5) and 207+/-59% (n=4) in atrial myocytes from NF and FH,
respectively. The above findings suggest that in atrial myocytes obtai
ned from FH the beta-adrenoceptor numbers might be decreased but no im
pairment of the signal transduction cascade occurred beyond the GTP bi
nding proteins level.