Voltage-dependent Inactivation

Voltage-dependent inactivation is channel inactivation at depolarised membrane potentials. 

Further support for a link between voltage-dependent Ca2+ channel activity and KCa channel activity was the present observation that during a depolarization (after 200 ms) the time course of change in the open probability of Kca channels was similar to that of Ica as it inactivated. Since KCa channels themselves do not exhibit voltage-dependent inactivation at OmV, the reduction in the open probability of the channel presumably reflects... 

Dopamine acting via the D2 receptors has complex effects on Na+ currents. An increase in the amplitude of this current has been reported in a minority of cells (Surmeier et al., 1992a). These currents are also reduced in response to a D2 receptor activation by means of a negative shift in voltage dependence of steady-state inactivation (Surmeier et al., 1992a). In cells in which a D2-mediated decrease in Na+ current was measured, the decrease was due to a shift in the voltage dependent inactivation towards more hyperpolarized potentials. This would make no difference at hyperpolarized Down state potentials but a big difference at more depolarized Up state potentials, where the effect would be to reduce the Na+ current in most cells. 

Keynes I don t know the answer to that from the Patlak Ortiz data. In squid, in the models that we have built, we can explain everything kinetically and predict everything by assuming that there is a voltage-dependent inactivation that takes place, but you can get out of it to a further open state. 

T channel activation is required for ZP3-evoked Ca + elevations and for acrosome reactions. As discussed, fluorescent indicators report that ZP3 stimulation produces a sustained elevation of Ca j in sperm. It is unlikely that inward Ca + current through the T channel can completely account for this response. T channels exhibit rapid, voltage-dependent inactivation and do not produce sustained current (Armstrong and Matteson, 1985 Bean, 1985 Hille, 1992 Bean and McDonough, 1998). In fact, the time resolution of the systems utilized to record ZP3-dependent rises in Ca i are too slow to report T channel activation (Florman et al., 1989 Arnoult et al., 1996b). 

N-channel currents have been characterized in chromaffin cells of various species including bovine [57,69], pig [63], cat[64],rat[47],mouse[62],andhuman [65]. This current suffers voltage-dependent inactivation [34,70], but see reference [57], and is irreversibly blocked by co-conotoxin GVIA [11] and co-conotoxin MVllC [16,17] or reversibly blocked by co-conotoxin MVllD... 

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