K + Channels in Cardiomyocytes of the Pulmonate Snail Helix

Abstract

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.

Modulation of HCN channels in lateral septum by nicotine

“…2A) was estimated by subtracting values at the onset of hyperpolarizing currents/voltages (peak amplitude) from those at the end (steady-state). The I h current was recorded in the presence of 1 mM 4–aminopyridine (4–AP), 1 mM Co 2+ , 1 µM tetrodotoxin (TTX), or 100–300 µM Ba 2+ in order to isolate it from possible contamination by voltage dependent K + , L–type Ca 2+ , Na + and inward rectifier K + channels, respectively (Griffith, 1988; Kodirov et al, 2003; Kodirov et al, 2004). The current signals were filtered at 1 kHz and the sampling interval was 2.5–5 kHz.…”

Atrial granular cells of the snailAchatina fulicarelease proteins into hemolymph after stimulation of the heart nerve

“…In these molluscs the coordinated beats of atrium and ventricle underlie both regular action potentials (Zhuravlev et al, 2002) and responsible ion channels (Kodirov et al, 2004). The peculiar feature of the heart of gastropod molluscs is numerous granular cells (GCs) attached to the myocardial surface of the atrium.…”

The neuronal control of cardiac functions in Molluscs

“…3) triggered in cardiomyocytes (Elekes et al, 1973; Hill, 1974a, 1974b; Zhuravlev et al, 2002). Distinct ion channels contribute to the membrane potential and APs of cardiomyocytes in Molluscs (Wilkens, 1972a, 1972b; Curtis et al, 1999; Yeoman et al, 1999; Pereira Ferreira and Salomão, 2000; Kodirov et al, 2004), and their properties are to some extent comparable to mammals albeit resting membrane potential, −45 vs. −70 mV (Irisawa et al, 1967). The isolated ventricle of Mytilus contracts spontaneously despite the exclusion of Na + after a transient blockade lasting up to 10 min.…”

“…These currents are sensitive to Co 2+ and operate in a window range of ±60 mV. In addition to the abovementioned four papers, the TEA-sensitive K + channels have been described in Helix (Kodirov et al, 2004). …”