Edwin A. Richard

The Voltage-Dependent Chloride Channel of Torpedo Electroplax

Our intention in this chapter is to describe the remarkable functional properties—some would say the eccentric behavior—of an anion transport protein found in the electric organ of electric rays, such as Torpedo and Narke. This is a Cl−-specific ion channel, commonly called the “Torpedo Cl− channel.” Like all ion channels, this protein catalyzes the electrodiffusive, thermodynamically downhill flow of ions across the membrane in which it resides, and thus should be classed as a membrane “leak.” Lest this term be considered pejorative by those familiar with active transporters which work to build up transmembrane ion gradients, we should point out that cells have good reasons to maintain specific leaks across their membranes; for instance, a leak for Cl−, in combination with a Cl− concentration gradient, can give rise to a transmembrane voltage, as is, we imagine, the purpose of the Torpedo Cl− channel.

Simultaneous Roles for Ca2+ in Excitation and Adaptation of Limulus Ventral Photoreceptors

The ventral photoreceptors of Limulus have been one of the main preparations for the study of invertebrate phototransduction. The study of ventral photoreceptors has revealed that they have remarkable performance characteristics, most notably the very large amplification of the transduction process. This amplification is critically dependent upon the coupling of photoactivated rhodopsin to the phosphoinositide cascade, resulting in the release of Ca2+ from intracellular stores. The consequent elevation of Ca2+ within the photoreceptors cytosol is amongst the most rapid and dramatic known to be activated by the phosphoinositide cascade. This review summarizes the evidence that intracellular Ca2+ is a key regulator of transduction in Limulus photoreceptors. The mechanisms that regulate Ca2+ as well as the possible targets of the action of Ca2+ are reviewed. Ca2+ elevation is critical for triggering both excitation and adaptation processes in the photoreceptor. The question of how a single second messenger can produce these two opposing effects is of obvious interest and is a topic dealt with throughout this review.

Potential synergistic action of 19 schizophrenia risk genes in the thalamus

A goal of current schizophrenia (SZ) research is to understand how multiple risk genes work together with environmental factors to produce the disease. In schizophrenia, there is elevated delta frequency EEG power in the awake state, an elevation that can be mimicked in rodents by N-methyl-d-aspartate receptor (NMDAR) antagonist action in the thalamus. This thalamic delta can be blocked by dopamine D2 receptor antagonists, agents known to be therapeutic in SZ. Experiments suggest that these oscillations can interfere with brain function and may thus be causal in producing psychosis. Here we evaluate the question of whether well-established schizophrenia risk genes may interact to affect the delta generation process. We identify 19 risk genes that can plausibly work in a synergistic fashion to generate delta oscillations.