Down regulation of sodium channels in the central nervous system of hibernating snails.

Hibernation, as behavior, is an evolutionary mode of adaptation of animal species to unfavorable environmental conditions. It is generally characterized by suppressed metabolism, which also includes down regulation of the energy consuming ion-channel functioning. Experimental data regarding decreased ion-channel function are scarce. Therefore, our goal was to study the possible down regulation of voltage-gated sodium channel (NaV) subtypes in the neurons of hibernating snails. Our immunohistochemical experiments revealed that the expression of NaV1.8-like channels in the central nervous system was substantially down regulated in hibernating animals. In contrast to NaV1.8-like, the NaV1.9-like channels were present in neurons independently from hibernating and non-hibernating states. Our western blot data supported the immunohistochemical results according to which the band of the NaV1.8-like channel protein was less intensively labeled in the homogenate of the hibernating snails. The NaV1.9-like immunoreactivity was equally present both in hibernating and active snails. Micro-electrophysiological experiments show that in hibernating snails both NaV1.8- and NaV1.9-like currents are substantially decreased compared to that of the active snails. The contradictory electrophysiological and immunohistochemical or western blot data suggest that the molecular mechanisms of the "channel arrest" could be different in diverse NaV channel subtypes. Climate changes will affect temperature extremes and a question is how different species beyond their physiological tolerance will or able to adapt to changing environment. Hibernation is an important mode of adaptation to extreme climatic variations, and pursuant to this the present results may contribute to the study of the behavioral ecology.

Potassium channels in the central nervous system of the snail, Helix pomatia: localization and functional characterization.

The distribution and functional presence of three voltage-dependent potassium channels, Kv2.1, Kv3.4, Kv4.3, respectively, were studied in the central nervous system of the snail Helix pomatia by immunohistochemical and electrophysiological methods. Cell clusters displaying immunoreactivity for the different channels were observed in all parts of the CNS, although their localization and number partly varied. Differences were also found in their intracellular, perikaryonal and axonal localization, as well as in their presence in non-neuronal tissues nearby the CNS, such as the perineurium and the aorta wall. At ultrastructural level Kv4.3 channel immunolabeling was observed in axon profiles containing large 80-100nm granular vesicles. Blotting analyses revealed specific signals for the Kv2.1, Kv3.4 and Kv4.3 channels, confirming the presence of the channels in the Helix CNS. Voltage-clamp recordings proved that outward currents obtained from neurons displaying Kv3.4 or Kv4.3 immunoreactivity contained transient components while Kv2.1 immunoreactive cells were characterized by delayed currents. The distribution of the K(+)-channels containing neurons suggests specific roles in intercellular signaling processes in the Helix CNS, most probably related to well-defined, partly local events. The cellular localization of the K(+)-channels studied supports their involvement in both pre- and postsynaptic events at perikaryonal and axonal levels.

Voltage-gated membrane currents in neurons involved in odor information processing in snail procerebrum.

The procerebrum (PC) of the snail brain is a critical region for odor discrimination and odor learning. The morphological organization and physiological function of the PC has been intensively investigated in several gastropod species; however, the presence and distribution of ion channels in bursting and non-bursting cells has not yet been described. Therefore, the aim of our study was to identify the different ion channels present in PC neurons. Based on whole cell patch-clamp and immunohistochemical experiments, we show that Na(+)-, Ca(2+)-, and K(+)-dependent voltage-gated channels are differentially localized and expressed in the cells of the PC. Different Na-channel subtypes are present in large (10-15 µm) and small (5-8 µm) diameter neurons, which are thought to correspond to the bursting and non-bursting cells, respectively. Here, we show that the bursting neurons possess fast sodium current (I NaT) and NaV1.9-like channels and the non-bursting neurons possess slow sodium current (I NaT) and NaV1.8-like channels in addition to the L-type Ca(-), KV4.3 (A-type K-channel) and KV2.1 channels. We suggest that the bursting and/or non-bursting character of the PC neurons is at least partly determined by the battery of ion-channels present and their cellular and subcellular compartmentalization.