Chloride dependent intracellular pH effects of external ATP in cultured human non-pigmented ciliary body epithelium

Receptor-independent effects of 2'(3')-O-(4-benzoylbenzoyl)ATP triethylammonium salt on cytosolic pH

The effect of the relatively potent P2X7 receptor agonist 2'(3')-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate triethylammonium salt (BzATP-TEA) on cytosolic pH (pHi) was studied using MC3T3-E1 osteoblast-like cells, which endogenously express P2X7 receptors. pHi was measured fluorimetrically using the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. BzATP-TEA (0.3-1.5 mM) elicited fast-onset alkalinization responses. In contrast, adenosine 5'-triphosphate disodium salt (5 mM) failed to reproduce the BzATP-TEA-induced responses, indicating a P2 receptor-independent mechanism. We speculated that triethylamine, which is present in solutions of BzATP-TEA, permeates the plasma membrane, and is protonated intracellularly, leading to an increase in pHi. Consistent with this hypothesis, triethylammonium (TEA) chloride mimicked the effects of BzATP-TEA on pHi. Moreover, measurements using a Cytosensor microphysiometer revealed that TEA chloride transiently suppressed proton efflux from cells, whereas washout of TEA transiently enhanced proton efflux. BzATP-TEA also elicited a sustained increase in proton efflux that was blocked specifically by the P2X7 antagonist A-438079. Taken together, we conclude that BzATP-TEA-induced alkalinization is unrelated to P2X7 activation, but is due to the presence of TEA. This effect may confound assessment of the outcomes of P2X7 activation by BzATP-TEA in other systems. Thus, control experiments using TEA chloride are recommended to distinguish between receptor-mediated and nonspecific effects of this widely used agonist. We performed such a control and confirmed that BzATP-TEA, but not TEA chloride, caused the elevation of cytosolic free Ca(2+) in MC3T3-E1 cells, ruling out the possibility that receptor-independent effects on pHi underlie BzATP-TEA-induced Ca(2+) signaling.

Nucleotides in the eye: focus on functional aspects and therapeutic perspectives

The presence and activity of nucleotides and dinucleotides in the physiology of most, if not all, organisms, from bacteria to humans, have been recognized by the scientific community, and the eye is no exception. Nucleotides in the dynamic fluids interact with many ocular structures, such as the tears and aqueous humor. Moreover, high concentrations of nucleotides in these secretions may reflect disease states such as dry eye and glaucoma. Apart from the nucleotide concentration in these fluids, P2 purinergic receptors have been described on the ocular surface (cornea and conjunctiva), anterior pole (ciliary body, trabecular meshwork), and posterior pole (retina). P2X and P2Y purinergic receptors are essential in maintaining the homeostasis of ocular processes, such as tear secretion, aqueous humor production, or retinal modulation. When they are functioning properly, they allow the eye to do its job (to see), but in some cases, a lack or an excess of nucleotides or a malfunction in the corresponding purinergic receptors leads to disease. This Perspective is focused on the nucleotides and dinucleotides and the P2 purinergic receptors in the eye and how they contribute to normal and disease states. We also emphasize the action of nucleotides and their receptors and antagonists as potential therapeutic agents.

Voltage-Gated Calcium Channels and Idiopathic Generalized Epilepsies

The idiopathic generalized epilepsies encompass a class of epileptic seizure types that exhibit a polygenic and heritable etiology. Advances in molecular biology and genetics have implicated defects in certain types of voltage-gated calcium channels and their ancillary subunits as important players in this form of epilepsy. Both T-type and P/Q-type channels appear to mediate important contributions to seizure genesis, modulation of network activity, and genetic seizure susceptibility. Here, we provide a comprehensive overview of the roles of these channels and associated subunits in normal and pathological brain activity within the context of idiopathic generalized epilepsy.