Patch clamp method developed more than 30 years ago is widely used for investigation of cellular excitability manifested as transmembrane ionic current and/or generation of action potentials. This technique could be applied to measurement of ionic currents flowing through individual (single) ion channels or through the whole assembly of ion channels expressed in the whole cell. Whole cell configuration is more common for measurement of ion currents and the only one enabling measurement of action potentials. This method allows detailed analysis of mechanisms and structural determinants of voltagedependent gating of ion channels as well as regulation of channel activity by intracellular signaling pathways and pharmacological agents., M. Karmažínová, L'. Lacinová., and Obsahuje bibliografii a bibliografické odkazy
We have investigated slow inactivation in a rat axonal K+ channel, the I channel. Using voltage steps to potentials between -70 mV and +80 mV, from a holding potential of -100 mV, we observed a marked slowing of inactivation at positive potentials: the time constant was 4.5±0.4 s at -40 mV (mean ± S.E.M.), increasing to 14.7±2.0 s at +40 mV. Slowed inactivation at positive potentials is not consistent with published descriptions of C-type inactivation, but can be explained by models in which inactivation is preferentially from closed states (which have been developed for Kv2.1 and some Ca2+ channels). We tested two predictions of preferential closed-state models: inactivation should be more rapid during a train of brief pulses than during a long pulse to the same potential, and the cumulative inactivation measured with paired pulses should be greater than the inactivation at the same time during a continuous pulse. The I channel does not behave according to these predictions, indicating that preferential closed-state inactivation does not explain the slowing of inactivation we observe at positive potentials. Inactivation of the I channel therefore differs both from C-type inactivation, as presently understood, and from the inactivation of Kv2.1., A. Babes, E. Lörinczi, V. Ristoiu, M.L. Flonta, G. Reid., and Obsahuje bibliografii