Mutant Analysis of the Shal (Kv4) Voltage-gated Fast Transient K+ Channel in Caenorhabditis elegans

Abstract

. We show that Shal channels also play a role as the predominant transient outward current in Caenorhabditis elegans muscle. Green fluorescent protein promoter experiments also revealed SHL-1 expression in a subset of neurons as well as in C. elegans body wall muscle and in male-specific diagonal muscles. The shl-1 (ok1168) null mutant removed all fast transient outward current from muscle cells. SHL-1 currents strongly resembled Shal currents in other species except that they were active in a more depolarized voltage range. We also determined that the remaining delayed-rectifier current in cultured myocytes was carried by the Shaker ortholog SHK-1. In shl-1 (ok1168) mutants there was a significant compensatory increase in the SHK-1 current. Male shl-1 (ok1168) animals exhibited reduced mating efficiency resulting from an apparent difficulty in locating the hermaphrodite vulva. SHL-1 channels are apparently important in fine-tuning complex behaviors, such as mating, that play a crucial role in the survival and propagation of the species.2 channels are key regulators of membrane excitability. Based on their inactivation kinetics, Kv currents can loosely be divided into two categories as follows: noninactivating or slowly inactivating K ϩ currents, and rapidly inactivating transient currents also known as "A-type" currents. A-type currents were first described in molluscan neurons by Hagiwara et al. (3) and later by Connor and Stevens (4), Neher (5), and Thompson (6). Classical A-type currents (I A ) are voltage-dependent, Ca 2ϩ -independent K ϩ currents that undergo rapid activation and inactivation. The classical A-type currents activate at subthreshold voltages and recover from inactivation quickly compared with other Kv currents. They are also characterized by strong steady-state voltagedependent inactivation. Repolarization to potentials negative to Ϫ50 mV is typically required to restore channel availability. A-type currents have a widespread distribution and are abundantly expressed in neurons and cardiac and smooth muscle cells, where they are thought to play many important physiological roles (2, 7-11).Connor and Stevens (12) proposed that the I A may determine the interspike interval in repetitively firing neurons. Studies in cerebellar granule cells demonstrated a role for I A in determining the latency to first spike (13). I A has also been demonstrated to limit the back propagation of action potentials into the dendritic arbor (14), to impact long term potentiation in CA1 hippocampal neurons (15), to affect neuronal excitability in the visual cortex (16), and to modulate compartmentalization of membrane excitability in distal dendritic spines (17). Fast transient K ϩ currents in cardiac muscles contribute both to myocyte excitability (18) and to the fast repolarization phase of the cardiac action potential (2,8,19,20). Finally, the pharmacological block of channels that carry fast transient currents in gastrointestinal smooth muscle in mice supports the conclusion that the window currents carried by ...

KChIP-Like Auxiliary Subunits of Kv4 Channels Regulate Excitability of Muscle Cells and Control Male Turning Behavior during Mating inCaenorhabditis elegans

“…They not only promote the biogenesis of SHL-1 K ϩ current, but also modulate the current characteristics in muscle cells. Previous studies have demonstrated that the SHL-1 native channels activate in a more hyperpolarized voltage (ϳϪ14 mV shift) than the cloned channels expressed in heterologous systems (Santi et al, 2003;Fawcett et al, 2006;Wu et al, 2010). Our data reveal that the discrepancy could be due to the existence of ceKChIPs.…”

“…Since then, the components of K ϩ currents in muscle cells have been well documented. Three K ϩ channels, SHK-1, SHL-1, and SLO-2, were reported to constitute the macroscopic outward K ϩ currents in muscle cells (Yuan et al, 2000;Santi et al, 2003;Fawcett et al, 2006;Gao and Zhen, 2011;Liu et al, 2011). Under physiological conditions with low intracellular concentrations of Cl Ϫ (4 -10 mM) and Ca 2ϩ (10 -100 nM), K ϩ currents with typical fast transient outward components were elicited by a series of voltage steps applied from Ϫ80 to ϩ80 mV (in 20 mV increments) from a holding potential of Ϫ80 mV in cultured myocytes of N2 worms (Fig.…”

A New Mode of Regulation of N-type Inactivation in a Caenorhabditis elegans Voltage-gated Potassium Channel

“…1) in the N terminus of KVS-1 (dubbed K1 in this "Result" section) exhibited homology to the N-inactivating domains in several A-type ␣-and ␤-subunits (7,9,(35)(36)(37)(38). This suggests that inactivation in K1 might proceed through a N-type mechanism.…”

Cumulative Activation of Voltage-Dependent KVS-1 Potassium Channels

“…positive voltage range than their mammalian counterparts. We showed this to be true for the Shaker (Kv1) and Shal (Kv4) channels (Fawcett et al, 2006) and Shaw (Kv3) EGL-36 channels (Johnstone et al, 1997). In fact, an egl-36 mutation that shifted the voltage dependence of activation of Shaw EGL-36 channels to more negative voltages typical of mammalian channels resulted in excessively active Shaw EGL-36 channels producing the egl phenotype.…”

“…Figure 2 A shows a family of KVS-1 currents expressed in Xenopus oocytes and evoked by depolarizing step pulses to progressively more positive voltages using two-electrode voltage clamp (TEV). In comparison, Figure 2 B shows a family of currents from the C. elegans Shal (Kv4) ortholog (nShal) (Fawcett et al, 2006). These two families of currents resemble each other with regard to their fast activation and rapid inactivation.…”