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Voltage‐ and cation‐dependent inactivation of L‐type Ca 2+ channel currents in guinea‐pig ventricular myocytes
Author(s) -
Findlay Ian
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.019729
Subject(s) - myocyte , depolarization , chemistry , biophysics , stimulation , patch clamp , voltage clamp , membrane potential , endocrinology , biology , biochemistry , receptor
L‐type Ca 2+ channel currents in native ventricular myocytes inactivate according to voltage‐ and Ca 2+ ‐dependent processes. This study sought to examine the effect of β‐adrenergic stimulation on the contributions of voltage and Ca 2+ to Ca 2+ current decay. Ventricular myocytes were enzymatically isolated from guinea‐pig hearts. Inward whole‐cell Cd 2+ ‐sensitive L‐type Ca 2+ channel currents were recorded with the patch clamp technique and comparison was made between inward currents carried by Ca 2+ and either Ba 2+ , Sr 2+ or Na + . In control conditions the decay of Ca 2+ currents was faster than Ba 2+ , Sr 2+ or Na + currents at negative voltages while at positive voltages there was no difference. The relationship between voltage and inactivation for Ca 2+ currents was bell‐shaped, while that for Ba 2+ , Sr 2+ , and Na + currents was sigmoid. Thus depolarisation progressively replaced Ca 2+ ‐dependent inactivation in the fast phase of decay of Ca 2+ channel currents with rapid voltage‐dependent inactivation. In the presence of isoproterenol (isoprenaline) the decay of Ca 2+ currents was faster than Ba 2+ , Sr 2+ or Na + currents at all measured voltages (‐40 to +30 mV). The relationship between voltage and inactivation for Ca 2+ , Ba 2+ and Sr 2+ currents was bell‐shaped, while that for Na + currents was sigmoid with less inactivation than under control conditions. Therefore the fast phase of decay of Ca 2+ channel currents was now almost entirely due to Ca 2+ . It is concluded that the relative contributions of Ca 2+ ‐ and voltage‐dependent mechanisms of inactivation of L‐type Ca 2+ channels in native cardiac myocytes are modulated by β‐adrenergic stimulation influencing the amount of rapid voltage‐dependent inactivation.