Ia. Hobai et al., Inhibition by nickel of the L-type Ca channel in guinea pig ventricular myocytes and effect of internal cAMP, AM J P-HEAR, 279(2), 2000, pp. H692-H701
Citations number
36
Categorie Soggetti
Cardiovascular & Hematology Research
Journal title
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY
The characteristics of nickel (Ni) block of L-type Ca current (I-Ca,I-L) we
re studied in whole cell patch-clamped guinea pig cardiac myocytes at 37 de
grees C in the absence and presence of 100 mu M cAMP in the pipette solutio
n. Ni block of peak I-Ca,I-L had a dissociation constant (K-d) of 0.33 +/-
0.03 mM in the absence of cAMP, whereas in the presence of cAMP, the K-d wa
s 0.53 +/- 0.05 mM (P = 0.006). Ni blocked Ca entry via Ca channels (measur
ed as I-Ca,I-L integral over 50 ms) with similar kinetics (K-d of 0.35 +/-
0.03 mM in cAMP-free solution and 0.30 +/- 0.02 mM in solution with cAMP, P
= not significant). Under both conditions, 5 mM Ni produced a maximal bloc
k that was complete for the first pulse after application. Ni block of I-Ca
,I-L was largely use independent. Ni (0.5 mM) induced a positive shift (4 t
o 6 mV) in the activation curve of I-Ca,I-L. The block of I-Ca,I-L by 0.5 m
M Ni was independent of prepulse membrane potential (over the range of -120
to -40 mV). Ni (0.5 mM) also induced a significant shift in I-Ca,I-L inact
ivation: by 6 mV negative in cAMP-free solution and by 4 mV positive in cel
ls dialyzed with 100 mM cAMP. These data suggest that, in addition to block
ing channel conductance by binding to a site in the channel pore, Ni may bi
nd to a second site that influences the voltage-dependent gating of the L-t
ype Ca channel. They also suggest that Ca channel phosphorylation causes a
conformational change that alters some effects of Ni. The results may be re
levant to excitation-contraction coupling studies, which have employed inte
rnal cAMP dialysis, and where Ni has been used to block I-Ca,I-L and Ca ent
ry into cardiac cells.