Phospholamban deficiency alters inactivation kinetics of L-type Ca2+ channels in mouse ventricular myocytes.
Entry of Ca2+ through voltage-dependent L-type Ca2+ channels is critical for contraction in cardiac cells. In recent studies, cells from phospholamban (PLB) knockout (PLB-KO) mouse hearts showed significantly increased basal contractility with enhanced sarcoplasmic reticulum (SR) Ca2+ uptake. To test whether these effects of PLB ablation were associated with alterations of L-type Ca2+ channel function, we compared the properties of Ca2+ channel currents (I(Ca)) in ventricular myocytes isolated from wild-type (WT) and PLB-KO mouse hearts. L-type Ca2+ channels from mouse myocytes exhibited voltage-dependent gating and sensitivity to dihydropyridine drugs, similar to other mammalian species, and these properties were not altered by PLB ablation. I(Ca) from both WT and PLB-KO cells revealed two (fast and slow) components of inactivation kinetics. However, the proportion of the faster component was significantly larger in PLB-KO cells. Ryanodine (10 microM) reduced the rate of inactivation of I(Ca) for both WT and PLB-KO cells, but the reduction was more prominent in PLB-KO cells compared with WT cells. In contrast, the inactivation in a Ba2+ solution could be fitted by a single exponential similar to the slower component in Ca2+, and this was not altered in PLB-KO cells. The increase in the fast Ca2+-dependent inactivation component in PLB-KO cells supports the hypothesis that Ca2+ released from the SR regulates Ca2+ channel inactivation by affecting the levels of Ca2+ near the channel and suggests that this may be an important compensatory mechanism in the hyperdynamic PLB-KO heart.
Masaki
H
H
Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Ohio 45267, USA.
Sato
Y
Y
Luo
W
W
Kranias
E G
EG
Yatani
A
A
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000172:deficiency*; D004095:Dihydropyridines / Q000494:pharmacology; D006352:Heart Ventricles; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D013997:Time Factors; D000099211:Phospholamban
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D004095:Dihydropyridines; D000099211:Phospholamban