Voltage- and cation-dependent inactivation of L-type Ca2+ channel currents in guinea-pig ventricular myocytes

L-type Ca2+ channel currents in native ventricular myocytes inactivate according to voltage- and Ca2+-dependent processes. This study sought to examine the effect of β-adrenergic stimulation on the contributions of voltage and Ca2+ to Ca2+ current decay. Ventricular myocytes were enzymatically isolated from guinea-pig hearts. Inward whole-cell Cd2+-sensitive L-type Ca2+ channel currents were recorded with the patch clamp technique and comparison was made between inward currents carried by Ca2+ and either Ba2+, Sr2+ or Na+. In control conditions the decay of Ca2+ currents was faster than Ba2+, Sr2+ or Na+ currents at negative voltages while at positive voltages there was no difference. The relationship between voltage and inactivation for Ca2+ currents was bell-shaped, while that for Ba2+, Sr2+, and Na+ currents was sigmoid. Thus depolarisation progressively replaced Ca2+-dependent inactivation in the fast phase of decay of Ca2+ channel currents with rapid voltage-dependent inactivation. In the presence of isoproterenol (isoprenaline) the decay of Ca2+ currents was faster than Ba2+, Sr2+ or Na+ currents at all measured voltages (-40 to +30 mV). The relationship between voltage and inactivation for Ca2+, Ba2+ and Sr2+ 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 Ca2+ channel currents was now almost entirely due to Ca2+. It is concluded that the relative contributions of Ca2+- and voltage-dependent mechanisms of inactivation of L-type Ca2+ channels in native cardiac myocytes are modulated by β-adrenergic stimulation influencing the amount of rapid voltage-dependent inactivation

Differentiate RNA single-stranded region of the branched structures and hairpin loops by an octahedral cobalt(II) complex

[[abstract]]Single-stranded RNA molecules usually include secondary structural elements such as bulges, internal loops, and hairpin loops. These RNA secondary structural elements are often essential for the biological activity and functions of the RNA molecule. Chemical probe CoII(HAPP)(TFA)2 in the presence of H2O2 is found to differentiate single-stranded RNA from branched structures and hairpin loops. This study uses CoII(HAPP)(TFA)2 to analyze the structures of two RNA molecules: a fragment of HIV TAR RNA (TAR-27) and the catalytic domain 5 of group II intron (D5-29). The electrophoretic mobility of TAR-27 does not shift in the presence of CoII(HAPP)(TFA)2, suggesting that the reagent does not change the conformation of RNA substrate. Cleavage of the RNA substrates by CoII(HAPP)(TFA)2 unambiguously differentiated RNA internal looped structures from hairpin loops. The results show that CoII(HAPP)(TFA)2 is a sensitive, informative and convenient tool for analysis of RNA secondary structures.[[notice]]補正完