ISSN:
1432-2013
Keywords:
cardiac myocytes
;
patch-clamp
;
L-type Ca2+ channels
;
Ca2+-induced inactivation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Ca2+ -induced inactivation of L-type Ca2+ channels is proposed as an important negative feedback mechanism regulating Ca2+ entry. Here, for the first time, evidence for modification of heart L-type Ca2+ channel activity by cytoplasmic calcium is provided from excised insideout membrane patches. Ba2+ currents through cardiac L-type Ca2+ channels exhibited only modest inactivation in the absence of cytoplasmic Ca2+. Elevation of cytoplasmic Ca2+ to micromolar concentrations strikingly affected L-type Ca2+ channel activity as evaluated from ensemble average Ba2+ currents. Inactivation was markedly increased concomitant with a reduction of peak inward current, which was almost completely eliminated at about 15 μM cytoplasmic Ca2+ concentration. Half maximal suppression of Ba2+ currents was observed at 2.3 μM Ca2+. The observed modifications of L-type Ca2+ channel activity show that cytoplasmic Ca2+ induces channel closure. Below 4 μM Ca2+, channels can be reversibly reactivated during repetitive depolarizations, while at high Ca2+ concentrations (∼15 μM) most Ca2+ channels reside in a closed state. This may allow for a delicate regulation of Ca2+ entry, and consequently of heart contraction.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00370266
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