KChIP1 and Frequenin Modify shal-Evoked Potassium Currents in Pyloric Neurons in the Lobster Stomatogastric Ganglion

Abstract

The transient potassium current (I(A)) plays an important role in shaping the firing properties of pyloric neurons in the stomatogastric ganglion (STG) of the spiny lobster, Panulirus interruptus. The shal gene encodes I(A) in pyloric neurons. However, when we over-expressed the lobster Shal protein by shal RNA injection into the pyloric dilator (PD) neuron, the increased I(A) had somewhat different properties from the endogenous I(A). The recently cloned K-channel interacting proteins (KChIPs) can modify vertebrate Kv4 channels in cloned cell lines. When we co-expressed hKChIP1 with lobster shal in Xenopus oocytes or lobster PD neurons, they produced A-currents resembling the endogenous I(A) in PD neurons; compared with currents evoked by shal alone, their voltage for half inactivation was depolarized, their kinetics of inactivation were slowed, and their recovery from inactivation was accelerated. We also co-expressed shal in PD neurons with lobster frequenin, which encodes a protein belonging to the same EF-hand family of Ca(2+) sensing proteins as hKChIP. Frequenin also restored most of properties of the shal-evoked currents to those of the endogenous A-currents, but the time course of recovery from inactivation was not corrected. These results suggest that lobster shal proteins normally interact with proteins in the KChIP/frequenin family to produce the transient potassium current in pyloric neurons.

A potassium channel (Kv4) cloned from the heart of the tunicateCiona intestinalisand its modulation by a KChIP subunit

“…In this paper we describe the modulation of kinetic and gating parameters of a tunicate Shal channel (CionaKv4) by a tunicate KChIP subunit (CionaKChIP), the first KChIP subunit cloned from either an invertebrate or a non-vertebrate chordate. Our data and those provided by Zhang et al (2003) on modulation of lobster Shal by KChIP1, are the first indications that modulation of Kv4 channels by KChIP subunits might be an ancient mechanism to modulate the excitability of electrically active tissues.…”

“…Therefore, it was not surprising that the message for a Kv4 channel was present in RNA extracted from the heart of the tunicate Ciona intestinalis, since these channels are known to mediate a transient current responsible for the 'notch' in cardiac action potentials from fish to mammals (Dixon et al, 1996;Brahmajothi et al, 1999;Nurmi and Vornanen, 2002;Roden et al, 2002). Similarly modulation of Kv4 mediated currents by KChIP and analogous calcium-binding accessory subunits is common across the Metazoa (Rosati et al, 2001;Zhang et al, 2003). Although genes for KChIP subunits have been identified by BLAST searches in the genomes of Drosophila and Anopheles, CionaKChIP is the first KChIP subunit from an invertebrate or non-vertebrate chordate that has been cloned and characterized.…”

“…Modulation of Kv4 channels by KChIP subunits is likely a conserved mechanism to modulate tissue excitability, because the effects of human KChIP1 on the lobster and mammalian Kv4 channels are similar (Zhang et al, 2003). Thus, KChIP1 increased current amplitude, slowed the rate of inactivation, and shifted activation and inactivation midpoints of lobster Kv4 channels (Zhang et al, 2003). In the present study, we address the question of how tunicate Shal is modulated by endogenous KChIP subunits.…”

“…All four KChIP isoforms modify the kinetics and gating properties of Kv4 channels Holmqvist et al, 2002). Modulation of Kv4 channels by KChIP subunits is likely a conserved mechanism to modulate tissue excitability, because the effects of human KChIP1 on the lobster and mammalian Kv4 channels are similar (Zhang et al, 2003). Thus, KChIP1 increased current amplitude, slowed the rate of inactivation, and shifted activation and inactivation midpoints of lobster Kv4 channels (Zhang et al, 2003).…”

Residues within the myristoylation motif determine intracellular targeting of the neuronal Ca2+ sensor protein KChIP1 to post-ER transport vesicles and traffic of Kv4 K+ channels

“…NCS-1 has previously been suggested to increase the channel density in Kv4-expressing cells although the effect was markedly smaller than that due to KChIPs, being only about a 70% increase (Guo et al, 2002;Nakamura et al, 2001). More recently, it was shown that both KChIP and NCS-1 modified the properties of Kv4 channels expressed in lobster neurons but only KChIP increased the current density (Zhang et al, 2003). In another study, direct interaction of NCS-1 with Kv4 α-subunits was apparently not observed (Ren and Takamoto, 2002) and so the extent of interaction between NCS-1 and Kv4 channels remains to be resolved but cannot be ruled out by the observations reported here.…”