[Superfamily of voltage dependent K+ channels: structure, functions and pathology].

In this review the recent studies related to the voltage dependent K+ channels are discussed. During the last 15 years the molecular cloning revealed a large number of alpha-subunits of voltage dependent K+ channels. This approach enabled to elucidate the properties of different types of channels and, in particular, characteristics of such structural elements as auxiliary subunits. These subunits are mainly responsible for the ionic permeability features of alpha-subunits. There are several cytoplasmic and membrane-associated auxiliary subunits such as beta-subunits, minK (minimal K+ channel peptide), MiRP (minK-related peptide), KChAP (K+ channel-associated protein), KChIP (K+ channel-interacting protein) and NCS (neuronal calcium sensor).

K+ channels in cardiomyocytes of the pulmonate snail helix.

We used the patch-clamp technique to identify and characterize the electrophysiological, biophysical, and pharmacological properties of K(+) channels in enzymatically dissociated ventricular cells of the land pulmonate snail Helix. The family of outward K(+) currents started to activate at -30 mV and the activation was faster at more depolarized potentials (time constants: at 0 mV 17.4 +/- 1.2 ms vs. 2.5 +/- 0.1 ms at + 60 mV). The current waveforms were similar to those of the A-type family of voltage-dependent K(+) currents encoded by Kv4.2 in mammals. Inactivation of the current was relatively fast, i.e., 50.2 +/- 1.8% of current was inactivated within 250 ms at + 40 mV. The recovery of K(+) channels from inactivation was relatively slow with a mean time constant of 1.7 +/- 0.2 s. Closer examination of steady-state inactivation kinetics revealed that the voltage dependency of inactivation was U-shaped, exhibiting less inactivation at more depolarized membrane potentials. On the basis of this phenomenon, we suggest that a channel encoded by Kv2.1 similar to that in mammals does exist in land pulmonates of the Helix genus. Outward currents were sensitive to 4-aminopyridine and tetraethylammonium chloride. The last compound was most effective, with an IC(50) of 336 +/- 142 micro mol l(-1). Thus, using distinct pharmacological and biophysical tools we identified different types of voltage-gated K(+) channels.

Long-term restitution of 4-aminopyridine-sensitive currents in Kv1DN ventricular myocytes using adeno-associated virus-mediated delivery of Kv1.5.

Overexpression of a dominant-negative truncated Kv1.1 (Kv1DN) polypeptide in the mouse heart resulted in marked attenuation of a 4-aminopyridine (4-AP)-sensitive current, I(K,slow1). We used recombinant adeno-associated virus (rAAV) as a vector for direct delivery of Kv1.5 into the mouse myocardium in order to normalize the action potential duration (APD) 6 months after injection. The injection of rAAV-Kv1.5 reconstituted the 4-AP-sensitive outward potassium currents, shortened the APD, and eliminated spontaneous early afterdepolarizations. Immunoblots detected the FL-Kv1.5 polypeptides only in rAAV-Kv1.5-infected hearts. These data demonstrate long-term expression of 4-AP-sensitive potassium currents in ventricular myocytes by gene transfer using rAAV vector encodes Kv1.5.

Giant multimodal heart motoneurons of Achatina fulica: a new cardioregulatory input in pulmonates.

The regulation of the heartbeat by the two largest neurons, d-VLN and d-RPLN, on the dorsal surface of visceral and right parietal ganglia of Giant African snail, Achatina fulica, was examined. Using the new method of animal preparation, for the first time, discrete biphasic inhibitory-excitatory junction potentials (I-EJPs) in the heart and several muscles of the visceral sac were recorded. The duration of hyperpolarizing phase (H-phase) of biphasic I-EJPs was 269+/-5.6 ms (n=5), which is 2-3 times less than that of the cholinergic inhibitory JPs (682+/-68.5 ms, n=5). The H-phase of I-EJPs was not altered by the application of atropine, picrotoxine, succinylcholinchloride, D-tubocurarine and tetraethylammonium or substitution of Cl(-) ions. Even the low-frequency neuronal discharges (1-2 imp/s) evoked significant facilitation and potentiation of the H-phase. Between the multimodal neurons d-VLN/d-RPLN and mantle or visceral organs there is evidence of direct synaptic connections. These neurons were found to have no axonal branches in the intestinal nerve as once suspected but reach the heart through several other nerves. New giant heart motoneurons do not interact with previously identified cardioregulatory neurons.

Participation of the Ca(2+)-calmodulin-activated Kinase II in the control of metaphase-anaphase transition in human cells.

Treatment of HeLa S3 cells growing in suspension, and of endothelial cells ECV 304 growing as a monolayer, with the inhibitor of the Ca(2+)-calmodulin activated Kinase II KN-93, blocks cells at metaphase for 15 min (HeLa cells) and 30 min (ECV cells). Thereafter cells resume mitosis and enter anaphase. The inactive isomer KN-92 does not show such effects. The results show the involvement of the CaM K II system in the regulation of the metaphase-anaphase transition whereby the activation of the Kinase II, in particular by calmodulin appears to be affected, the residual autophosphorylation of the CaM K II system apparently sufficing after 15 to 30 min to release the cells into anaphase. The results are compared with the metaphase-blocking effects of the noble gas xenon, where the xenon-induced block can be overcome by small intracellular increases of Ca(2+), thus indicating the CaM K II system as a possible target for xenon.

The chronoinotropic effects of new regulatory input to the heart of land pulmonates.

The postjunctional potentials and chronoinotropic reactions of the heart evoked by activation of multimodal neurons and/or left pallial nerve were investigated in three species of land pulmonates: Achatina fulica Ferrussac, Helix lucorum L., Arianta arbustorum L. Both spikes of giant homologous neurons (d-VLN, d-RPLN by A. fulica, command neurons of pneumostoma LPa3, RPa3 by H. lucorum) and stimulation of the peripheral end of the left pallial nerve evoked the similar biphasic inhibitory-excitatory junction potentials in the heart, in mantle muscles and in different parts of visceral complex. The positive chronoinotropic effects of this input in the hearts of whole-mount preparations were modified due to interaction with well-known neural cardioregulating network of the system of intestinal nerve.