We studied some of the physiological and pharmacological properties of an in vitro model of epileptic seizures induced by elevation of [K+]0 (to 8 mM and 10 mM) in combination with lowering of [Mg2+]0 (to 1.4 mM and 1.6 mM) and [Ca2+]0 (to 0.7 mM and 1 mM) in rat hippocampal slices. These concentrations correspond to the ionic constitution of the extracellular microenvironment during seizures in vivo. The resulting activity was rather variable in appearance. In area CA3 recurrent discharges were observed which resulted in seizure-like events with either clonic-like or tonic-clonic-like ictaform events in area CA1. With ion-sensitive electrodes, we measured the field potential and the changes in extracellular ion concentrations which accompany this activity. The recurrent discharges in area CA3 were accompanied by small fluctuations in [K+]0 and [Ca2+]0. The grouped clonic-like discharges in area CA1 were associated with moderate increases in [K+]0 and small decreases in [Ca2+]0 in the order of 2 mM and 0.2 mM, respectively. Large, negative field-potential shifts and increases in [K+]0 to 13 mM, as well as decreases in [Ca2+]0 by up to 0.4 mM, accompanied the tonic phase of ictaform events. The ictaform events were not blocked by D-2-aminophosphonovalerate (2-APV) but were sensitive to 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) alone and in combination with 2-APV and ketamine. In order to determine the pharmacological characteristics of the ictaform events we bath-applied most clinically employed anticonvulsants (carbamazepine, phenytoin, valproate, phenobarbital, ethosuximide, trimethadione) and some experimental anticonvulsants (losigamone, vinpocetine, and apovincaminic acid). Carbamazepine, phenytoin, valproate, and phenobarbital were effective at clinically relevant doses. The data suggest that the high-K+ model of epileptiform activity is a good model of focal convulsant activity.

Three-dimensional cell aggregates (embryoid bodies, EBs) containing clusters of spontaneously beating cardiomyocytes were derived from permanent mouse embryonic stem (ES) cells. Extracellular recordings of the population action potentials of cardiomyocyte clusters were made using permanently mounted silver wire electrodes and microelectrode arrays integrated into the bottom of the culture dish. These techniques allowed long-term recordings (for up to several weeks) from individual EBs under cell culture conditions. The normal electrical activity consisted of regular spiking with a frequency of 0.5-5 Hz. However, most EBs (87%) spontaneously developed temporary or persistent complex activity patterns because of intermittent block of action potential propagation at narrow pathways connecting larger beating areas. Similar propagation blocks could also be reversibly induced in regularly spiking EBs by nimodipine (NDP). In addition to a slowing of pacemaker activity, NDP (20-200 nM) induced a stepwise decrease of the action potential frequency at the recording site. Perforated patch-clamp recordings from enzymatically isolated ES-cell-derived cardiomyocytes showed that similar activity patterns do not occur at the single-cell level. We suggest that this novel approach may provide a useful tool for in vitro studies of chronotropy and phenomena of propagation failure similar to AV block.

In the whip spider Heterophrynus elaphus the first pair of legs is specialized to serve sensory functions. The morphology of these "whips" and the sensory organs of their tarsi and tibiae are described using scanning and transmission electron microscopy. The tarsus is normally subdivided into 74 segments and bears 7 types of sensory hairs: bristles, club sensilla, two types of porous sensilla, two types of rod sensilla, and leaflike hairs. In addition there are modified claws, 3 kinds of slit sense organs, a "pit organ," a "plate organ," and probably a joint receptor. The tibia is usually subdivided into 33 segments. In addition to bristles the tibia bears 7 trichobothria at constant locations and a lyriform slit sense organ. The functional and systematic implications of these findings are discussed.

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Extracellular recordings of spontaneous electrical activity in contracting cardiac clusters differentiated from murine embryonic stem cells enable to study electrophysiological features of this in-vitro cardiac-like tissue as well as effects of pharmacological compounds on its chronotropy and electrical conduction. To test if the microelectrode array (MEA) system could serve as a basis for development of a pharmacological screening tool for cardioactive drugs, we used spontaneously beating outgrowths of three-dimensional ES cell aggregates (“embryoid bodies”, EBs) plated onto substrate-integrated MEAs. The effects of the L-type Ca²⁺ channel antagonist verapamil and Na⁺ and K⁺ channel blockers (tetrodotoxin, 4-aminopyridine, and sparfloxacin) on the deduced interrelated cardiac network function were investigated. Application of 10^-6 M verapamil led to arrhythmic spiking with a burst-like pattern; at a higher concentration (10^-5 M) the drug caused a sustained negative chronotropy up to complete stop of beating. In the presence of tetrodotoxin a conduction block was observed. Since modulation of K⁺ channel activity can cause anti- or proarrhythmic effects, the influence of K⁺ channel blockers, namely 4-aminopyridine and sparfloxacin, was investigated. 4-aminopyridine (2x10^-3 M) significantly stabilized beating frequency, while the field potential duration (FPD) was concentration-dependently prolonged up to 2.7-fold. Sparfloxacin (3x10^-6 M) stabilized the beating frequency as well. At a higher concentration of sparfloxacin (3x10^-5 M), a significant prolongation of the spike duration was registered; application of the drug caused also early afterdepolarizations. The results demonstrate a suitability of the studied in-vitro cardiac cell model for pharmacological drug testing in cardiovascular research.

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