Direct inhibition of expressed cardiac l- and t-type calcium channels by igg from mothers whose children have congenital heart block.
BACKGROUND
Congenital heart block (CHB) is a disease that affects the offspring of mothers with autoimmune diseases. We recently reported that maternal sera containing antibodies against SSA/Ro and SSB/La ribonucleoproteins (positive IgG) inhibited L-type Ca current in isolated cardiac myocytes and induced sinus bradycardia in a murine model of CHB. The direct interaction of positive IgG with L-type Ca channel proteins and the possible inhibition of T-type Ca current that could account for the sinus bradycardia remain unknown.


RESULTS
The 2-electrode voltage-clamp technique was used to record currents via L-type (I(Ba)-alpha(1C) or I(Ba)-alpha(1C)+beta(2a)+alpha(2)/delta) and T-type (I(Ba)-alpha(1H)) Ca channels, Na channels (I(Na)-hH1), and K channels (I(Ks)-minK+KvLQT1) expressed in Xenopus oocytes. Positive IgG (350 microgram/mL) inhibited I(Ba)-alpha(1C) by 50.6+/-4.7% (P<0.01) and I(Ba)-alpha(1C)+beta(2a)+alpha(2)/delta by 50.9+/-4.2% (P<0.01); I(Ba)-alpha(1H) was reduced by 18.9+/-1.0% (P<0.01). Immunoblot data show cross-reactivity of positive IgG with alpha(1C) subunit. Pretreatment of oocytes with atropine (1 micromol/L) or acetylcholine (10 micromol/L) did not affect the inhibitory effect of IgG on I(Ba)-alpha(1C) and I(Ba)-alpha(1C)+beta(2a)+alpha(2)/delta (P<0.05). Positive IgG had no effect, however, on either I(Na)-hH1 or I(Ks)-minK+KvLQT1.


CONCLUSIONS
Positive IgG inhibited expressed L-type I:(Ba) and cross-reacted with the alpha(1C) subunit in Xenopus oocytes, providing strong evidence that maternal antibodies interact directly with the pore-forming alpha(1)-subunit of Ca channels. In addition, we show for the first time that positive IgG also inhibited T-type I(Ba) but not I(Na)-hH1 or I(Ks)-minK+KvLQT1. This could provide, in part, the ionic basis of sinus bradycardia reported in animal models of CHB and clinically in humans.
Xiao
G Q
GQ
Molecular and Cellular Cardiology Program, New York Harbor Healthcare System and SUNY Health Science Center, Brooklyn, NY, USA.
Hu
K
K
Boutjdir
M
M
D000328:Adult; D000818:Animals; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D020747:Calcium Channels, T-Type / Q000187:drug effects / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D002648:Child; D003429:Cross Reactions; D004594:Electrophysiology; D005260:Female; D015870:Gene Expression; D006327:Heart Block / Q000151:congenital* / Q000235:genetics; D006801:Humans; D007074:Immunoglobulin G / Q000494:pharmacology*; D009035:Mothers; D009865:Oocytes; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D015222:Sodium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D014162:Transfection; D014982:Xenopus laevis
D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D007074:Immunoglobulin G; D015221:Potassium Channels; D015222:Sodium Channels