Chromaffin cells from mice lacking the BK β2 subunit show decreased action potential firing during current injection but an increase in spontaneous burst firing.

Two mammalian genes, Kcnt1 and Kcnt2, encode pore-forming subunits of Na+-dependent K+ (KNa) channels. Progress in understanding KNa channels has been hampered by the absence of specific tools and methods for rigorous KNa identification in native cells. Here, we report the genetic disruption of both Kcnt1 and Kcnt2, confirm the loss of Slo2.2 and Slo2.1 protein, respectively, in KO animals, and define tissues enriched in Slo2 expression. Noting the prevalence of Slo2.2 in dorsal root ganglion, we find that KO of Slo2.2, but not Slo2.1, results in enhanced itch and pain responses. In dissociated small diameter DRG neurons, KO of Slo2.2, but not Slo2.1, abolishes KNa current. Utilizing isolectin B4+ neurons, the absence of KNa current results in an increase in action potential (AP) firing and a decrease in AP threshold. Activation of KNa acts as a brake to initiation of the first depolarization-elicited AP with no discernible effect on afterhyperpolarizations.DOI: http://dx.doi.org/10.7554/eLife.10013.001

Adrenal chromaffin cells (CCs) are the main source of circulating catecholamines (CAs) that regulate the body response to stress. Release of CAs is controlled neurogenically by the activity of preganglionic sympathetic neurons through trains of action potentials (APs). APs in CCs are generated by robust depolarization following the activation of nicotinic and muscarinic receptors that are highly expressed in CCs. Bovine, rat, mouse, and human CCs also express a composite array of Na, K, and Ca channels that regulate the resting potential, shape the APs, and set the frequency of AP trains. AP trains of increasing frequency induce enhanced release of CAs. If the primary role of CCs is simply to relay preganglionic nerve commands to CA secretion, why should they express such a diverse set of ion channels? An answer to this comes from recent observations that, like in neurons, CCs undergo complex firing patterns of APs suggesting the existence of an intrinsic CC excitability (non-neurogenically controlled). Recent work has shown that CCs undergo occasional or persistent burst firing elicited by altered physiological conditions or deletion of pore-regulating auxiliary subunits. In this review, we aim to give a rationale to the role of the many ion channel types regulating CC excitability. We will first describe their functional properties and then analyze how they contribute to pacemaking, AP shape, and burst waveforms. We will also furnish clear indications on missing ion conductances that may be involved in pacemaking and highlight the contribution of the crucial channels involved in burst firing.

Heterotrimeric G proteins transduce signals sensed by transmembrane G protein coupled receptors (GPCRs). A subfamily of G protein βγ subunit types has been shown to selectively translocate from the plasma membrane to internal membranes on receptor activation. Using 4D imaging we show here that Gβγ translocation is not restricted to some subunit types but rather all twelve members of the family of mammalian γ subunits are capable of supporting βγ translocation. Translocation kinetics varies widely depending on the specific γ subunit type, with t1/2 ranging from 10 seconds to many minutes. Using fluorescence complementation, we show that the β and γ subunits translocate as βγ dimers with kinetics determined by the γ subunit type. The expression patterns of endogenous γ subunit types in HeLa cells, hippocampal neurons and cardiomyocytes are distinctly different. Consistent with these differences, the βγ translocation rates vary widely. βγ translocation rates exhibit the same γ subunit dependent trends regardless of the specific receptor type or cell type showing that the translocation rates are intrinsic to the γ subunit types. βγ complexes with widely different rates of translocation had differential effects on muscarinic stimulation of GIRK channel activity. These results show that G protein βγ translocation is a general response to activation of GPCRs and may play a role in regulating signaling activity.

The perception of sound relies on sensory hair cells in the cochlea that convert the mechanical energy of sound into release of glutamate onto postsynaptic auditory nerve fibers. The hair cell receptor potential regulates the strength of synaptic transmission and is shaped by a variety of voltage-dependent conductances. Among these conductances, the Ca2+- and voltage-activated large conductance Ca2+-activated K+channel (BK) current is prominent, and in mammalian inner hair cells (IHCs) displays unusual properties. First, BK currents activate at unprecedentedly negative membrane potentials (−60 mV) even in the absence of intracellular Ca2+elevations. Second, BK channels are positioned in clusters away from the voltage-dependent Ca2+channels that mediate glutamate release from IHCs. Here, we test the contributions of two recently identified leucine-rich-repeat–containing (LRRC) regulatory γ subunits, LRRC26 and LRRC52, to BK channel function and localization in mouse IHCs. Whereas BK currents and channel localization were unaltered in IHCs fromLrrc26knockout (KO) mice, BK current activation was shifted more than +200 mV in IHCs fromLrrc52KO mice. Furthermore, the absence of LRRC52 disrupted BK channel localization in the IHCs. Given that heterologous coexpression of LRRC52 with BK α subunits shifts BK current gating about −90 mV, to account for the profound change in BK activation range caused by removal of LRRC52, we suggest that additional factors may help define the IHC BK gating range. LRRC52, through stabilization of a macromolecular complex, may help retain some other components essential both for activation of BK currents at negative membrane potentials and for appropriate BK channel positioning.