NDLI: Sodium/calcium selectivity of cloned calcium T-type channels

Content Provider	Springer Nature Link
Author	Shcheglovitov, A. K. Shuba, Ya. M.
Copyright Year	2006
Abstract	We studied the peculiarities of permeability with respect to the main extracellular cations, Na$^{+}$ and Ca$^{2+}$, of cloned low-threshold calcium channels (LTCCs) of three subtypes, Ca$_{v}$3.1 (α1G), Ca$_{v}$3.2 (α 1H), and Ca$_{v}$3.3 (α1I), functionally expressed in Xenopus oocytes. In a calcium-free solution containing 100 mM Na$^{+}$ and 5 mM calcium-chelating EGTA buffer (to eliminate residual concentrations of Ca$^{2+}$) we observed considerable integral currents possessing the kinetics of inactivation typical of LTCCs and characterized by reversion potentials of −10 ± 1, −12 ± 1, and −18 ± 2 mV, respectively, for Ca$_{v}$3.1, Ca$_{v}$3.2, and Ca$_{v}$3.3 channels. The presence of Ca$^{2+}$ in the extracellular solution exerted an ambiguous effect on the examined currents. On the one hand, Ca$^{2+}$ effectively blocked the current of monovalent cations through cloned LTCCs (K $_{d}$ = 2, 10, and 18 µM for currents through channels Ca$_{v}$3.1, Ca$_{v}$3.2, and Ca$_{v}$3.3, respectively). On the other hand, at the concentration of 1 to 100 mM, Ca$^{2+}$ itself functioned as a carrier of the inward current. Despite the fact that the calcium current reached the level of saturation in the presence of 5 mM Ca$^{2+}$ in the external solution, extracellular Na$^{+}$ influenced the permeability of these channels even in the presence of 10 mM Ca$^{2+}$. The Ca$_{v}$3.3 channels were more permeable with respect to Na$^{+}$ (P $_{Ca}$/P $_{Na}$ ∼ 21) than Ca$_{v}$3.1 and Ca$_{v}$3.2 (P $_{Ca}$/P $_{Na}$ ∼ 66). As a whole, our data indicate that cloned LTCCs form multi-ion Ca$^{2+}$-selective pores, as these ions possess a high affinity for certain binding sites. Monovalent cations present together with Ca$^{2+}$ in the external solution modulate the calcium permeability of these channels. Among the above-mentioned subtypes, Ca$_{v}$3.3 channels show the minimum selectivity with respect to Ca$^{2+}$ and are most permeable for monovalent cations.
Starting Page	149
Ending Page	157
Page Count	9
File Format	PDF
ISSN	00902977
Journal	Neurophysiology
Volume Number	38
Issue Number	3
e-ISSN	15739007
Language	English
Publisher	Kluwer Academic Publishers-Consultants Bureau
Publisher Date	2006-01-01
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	calcium channels low-threshold T-type calcium channels selectivity permeability Ca$^{2+}$ Na$^{+}$ Neurosciences
Content Type	Text
Resource Type	Article
Subject	Neuroscience Physiology

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