Potassium current activated by intracellular sodium in quail trigeminal ganglion neurons.

Abstract

Whole-cell voltage clamp and singie-channel recordings were performed on cultured trigeminal ganglion neurons from quail embryos in order to study a sodium-activated potassium current (KNa). When KNa was activated by a step depolarization in voltage clamp, there was a proportionality between KNa and INa at all voltages between the threshold of Ina and ENa. Single-channel recordings indicated that KNa could be activated already by 12 mM intracellular sodium and was almost fully activated at 50 mM sodium. 100 mM lithium, 100 mM choline, or 5 tzM calcium did not activate KNa. The relationship between the probability for the channel to be open (Po) vs. the sodium concentration and the relationship of KNa open time-distributions vs. the sodium concentration suggest that two to three sodium ions bind cooperatively before KNa channels open. KN~ channels were sensitive to depolarization; at 12 mM sodium, a 42-mV depolarization caused an e-fold increase in Po. Under physiological conditions, the conductance of the K~ channel was 50 pS. This conductance increased to 174 pS when the intra-and extracellular potassium concentrations were 75 and 150 mM, respectively.

NAD+Activates KNaChannels in Dorsal Root Ganglion Neurons

“…However, it has been difficult to reconcile these diverse physiological functions with one apparent property of K Na channels: their requirement for high concentrations of [Na ϩ ] i to activate. The normal resting level of [Na ϩ ] i in neurons lies between 4 and 15 mM (Rose, 2002), and the effective concentrations required to activate 50% of channels (EC 50 ) have mostly been reported to range between 40 and 80 mM (Dryer, 1994), although some groups have reported much lower EC 50 s (Haimann et al, 1990;Dale, 1993). The two genes that encode K Na channels, Slack (Slo 2.2,kcnt1) and Slick (Slo 2.1, kcnt2) (Bhattacharjee and Kaczmarek, 2005;Salkoff et al, 2006), when expressed in CHO (Chinese hamster ovary) cells have EC 50 s of ϳ40 and ϳ80 mM, respectively (Bhattacharjee et al, 2003).…”

Kinetic properties of unitary Na+‐dependent K+ channels in inside‐out patches from isolated guinea‐pig ventricular myocytes.

“…A channel of this type activated by Nae (KNa) at the intracellular surface has been identified in both neuronal and myocardial cells at the whole-cell and single-channel level (Kameyama, Kakei, Sato, Shibasaki, Matsuda & Irisawa, 1984;Bader, Bernheim & Bertrand, 1985;Dryer, Fujii & Martin, 1989;Haimann, Bernheim, Bertrand & Bader, 1990;Luk & Carmeliet, 1990;Rodrigo & Chapman, 1990; Sanguinetti, 1990;Wang, Kimitsuki & Noma, 1991). These channels have a relatively high incidence in neuronal inside-out patches (20-38%) with significant activation at 10 mm Nai and maximal activation at 50 mm.…”

“…These channels have a relatively high incidence in neuronal inside-out patches (20-38%) with significant activation at 10 mm Nai and maximal activation at 50 mm. Consequently, they have been ascribed a role in the maintenance of the resting potential and in the repolarization of action potential (Haimann & Bader, 1989;Dryer, 1991;Haimann et al 1990). The KNa channels in cardiac muscle have a lower incidence (15-20%) and are less sensitive to Na, apparently requiring at least 30 mm Nat for activation and showing no saturation at 150 mm, features that have made their physiological role uncertain (Kameyama et al 1984;Sanguinetti, 1990;Wang et al 1991).…”

“…Indeed the differences between neuronal and cardiac KNa channels have been considered sufficient to justify their classification as separate subtypes (Haimann & Bader, 1989;Dale, 1993). At the single-channel level, both neuronal and cardiac KNa channels are typified by complex bursting behaviour with varying patterns of alternating episodes of activity and quiescence and the presence of numerous transient (probably 12 equal) substates (Kameyama et al 1984;Dryer et al 1989;Haimann et al 1990; Luk & Carmeliet, 1990;Sanguinetti, 1990;Wang et al 1991). Wang et al (1991) suggested that a multi-barrelled channel similar to that proposed for the inward rectifier was unlikely because K+ channel blockers revealed that the substates had similar properties, while Sanguinetti (1990) (Rodrigo & Chapman, 1990).…”

Kainate induces an intracellular Na+‐activated K+ current in cultured embryonic rat hippocampal neurones

“…The existence of K¤ channels gated by intracellular Na¤ (KNa) was first demonstrated in isolated guinea-pig ventricular myocytes (Kameyama et al 1984). Since then, this class of K¤ channels has been found in a wide variety of species and preparations, including neurones in crayfish (Hartung, 1985), Drosophila (Saito & Wu, 1991), snails (Partridge & Thomas, 1976), birds (Bader et al 1985;Dryer et al 1989;Haimann et al 1990Haimann et al , 1992Dryer, 1993) and mammals (Schwindt et al 1989;Egan et al 1992a,b). The physiological functions of this class of K¤ channels have been difficult to define largely because their activation usually requires Na¤ levels considerably higher Journal of Physiology (1998), 510.3, pp.…”