Functioning of K channels during sleep

Abstract

The functioning of voltage-dependent K channels (Kv) may correlate with the physiological state of brain in organisms, including the sleep in Drosophila. Apparently, all major types of K currents are expressed in CNS of this model organism. These are the Shab-Kv2, Shaker-Kv1, Shal-Kv4, and Shaw-Kv3 α subunits and can be deciphered by patch-clamp technique. Although it is plausible that some of these channels may play a prevailing role in sleep or wakefulness, several of recent data are not conclusive. It needs to be defined that indeed the frequency of action potentials in large ventral lateral pacemaker neurons is either higher or lower during the morning or night because of an increased Kv3 and Kv4 currents, respectively. The outcomes of dynamic-clamp approach in combination with electrophysiology in insects are unreliable in contrast to those in mammalian neurons. Since the addition of virtual Kv conductance during any Zeitgeber time should not significantly alter the resting membrane potential. This review explains the Drosophila sleep behavior based on neural activity with respect to K current-driven action potential rate.

Keywords: Kv1; Kv2; Kv3; Kv4; Patch-clamp; dynamic-clamp.

FIGURE 1

Family of neuronal outward K currents in Drosophila. (a) Current density in large LNV neurons upon −3 mV at tested ZT from an inadequate HP of −133 mV, as the RMP was −58 mV at highest. Box and Whiskers represent the median, inter-quartile range (IQR), and minimum–maximum values. Modified (Smith et al., 2019). Arrows point whether or not differences in densities of Shaw between ZT14 and ZT20 and that of Shal between ZT2 and ZT20 are significant. Note that these data do not overlap in range. (b–e) If traces reflect the averaged ones of, for example, n = 12, then they should be much smoother. Especially these traces in turn are respective and subtracted DTX-, GxTX-, BDS-, and PaTX-sensitive currents [object HTMLSpanElement](ɑ-Dendrotoxin, guangxitoxin-1E, blood-dispersingsubstance, and phrixotoxin-1, respectively). Thus, original traces have undergone two-time processing. Note the shorter time span for Shal. Mean peak values based on traces in D and digits in A for Shaw are apart ( at dashed line indicate the 30 pA/pF level). LNV, large ventral lateral; RMP, resting membrane potential

FIGURE 2

Behavior of family of outward K currents in Drosophila. (a) Part of subtracted Shaker currents from Figure 1b. Outward currents were activated upon −3 mV (the highest), −13, −23, and −33 mV. Despite the strong depolarization, remaining pulses triggered only small inward currents. The latter could also reflect that the DTX increased outward currents at these test steps. The symbol points to converging behavior of all traces. (b) Ordinary, the patch-clamp traces do not behave as presented for Shaw. If one chooses to present for “clarity” a certain portion of traces, the pClamp or any software truncates them at 90°, but not at 17°, 37°, and so forth. Even if it is performed by cut, copy, and paste, the angle is always 90°. Modified and highlighted (Smith et al., 2019)

FIGURE 3

Altering the rate of spontaneous spikes in large LNV neurons by dynamic-clamp approach. (a) Rate during morning before and after extra conductance of Shal. Highlighted (Smith et al., 2019). Note ~5 mV changes in RMP and the uncoordinated depolarization with that of currents in (b). Dashed boxes reflect changes in spike amplitude. (b) Corresponding current behavior. Arrows point whether the MP and spikes or currents are drivers. (c) Perhaps the same neuron in the presence of Shaw, since the proximate level of RMP is identical at −54 mV. Now an opposite effect is observed on RMP, though it is ~1.4 mV depolarization. The effects of the same type of channels cannot have opposite polarities. The latter is perhaps derived by artificially assigning the negative polarity for “removed” Shaw as −1.4 nS in (a) and Shal as −1.25 nS in (c). (d) Current behavior either in response to or followed by MP and spikes in (c). Note that in contrast to (a and b) pair, the behavior of (c and d) one are almost 100% similar. LNV, large ventral lateral; MP, membrane potential; RMP, resting membrane potential

FIGURE 4

Behavior of burst in large LNV neuron. (a) Three spikes in bursting mode from Figure 3a. (b) Dynamic-clamp currents are reflecting parameters of spikes, namely the rate and gradual MP depolarization after each AP. (c) Portion of trace from (a). It is impossible to truncate the last spike horizontally at 90°, at least not with Clampfit and as appear. (d) The same applies as to currents in (b). Modified and highlighted (Smith et al., 2019). AP, action potential; LNV, large ventral lateral; MP, membrane potential

FIGURE 5

Driver or follower? A portion of traces from Figure 3b,d in expanded amplitude and time scales. For good or worth, they are 100% homologous and symbol denotes one of hallmarks in both traces in space and time. Hyperpolarization is perhaps triggered by a “removed” Shaw (−1.4 nS), while depolarization by Shal (−1.25 nS) or else. If these currents are “outputs” then they cannot be identical. Otherwise, it is just a white noise, which is unable to alter the baseline spontaneous excitability and background MP fluctuations. Modified and highlighted (Smith et al., 2019). MP, membrane potential

FIGURE 6

Dynamic-clamp approach in mammals. Spontaneous pacemaking in three different cells of the same type—dopaminergic neurons of substantia nigra pars compacta in rat coronal midbrain slice. After 10 s baseline recordings, the virtual 100 nS Kv4.3 conductance—gK_A was applied temporarily for 40 s. This A-type K current is specific to recorded neurons. Note that the weaker pacemaker rate, the stronger are effects of gK_A. The onset and offset of effects are rapid. In upper neuron a decrease in rate has accompanied by a slight increase in overshoot peak and AHP—afterhyperpolarizing potential. During intermediate rate only the AHP is increased, while at higher spike frequency the peak and AHP are not affected. Highlighted (Putzier et al., 2009)