Calcium current in embryonic <i>Xenopus</i> muscle cells in culture

Moody-Corbett, F; Gilbert, Robert; Akbarali, Hamid I.; Hall, Johnathon M

doi:10.1139/y89-200

Cited by 14 publications

(1 citation statement)

References 13 publications

(28 reference statements)

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“…They have been designated I K , for the non-inactivating outward current, and I IK , for the inactivating outward current [17,33]. Two of the inward currents are mediated by calcium ions and show properties similar to the L-type and T-type calcium currents described in other muscle preparations [35]. Finally, a TTX-sensitive inward sodium current has been identified in these muscle cells in culture [14].…”

Section: Resultsmentioning

confidence: 97%

Localization of sodium and potassium currents at sites of nerve-muscle contact in embryonic Xenopus muscle cells in culture

Fry¹,

Moody-Corbett²

1999

Pfl�gers Archiv European Journal of Physiology

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Macro-patch current recordings were used to determine the spatial distribution of INa, inactivating (IIK) and non-inactivating (IK) outward potassium currents on nerve-contacted Xenopus muscle cells grown in culture. Sites of nerve contact were identified under 400x magnification and macroscopic currents recorded from cell-attached membrane patches ranging in diameter from 2 microm to 6 microm. Membrane patch (n=133) recordings revealed no detectable current, or INa and/or IIK, or just IK. More than 85% of the membrane patches from which INa (n=35) could be recorded occurred within 40 microm of the position of nerve contact. In addition, more than 90% of the membrane patches which contained INa also contained IIK. The density of IIK in these membrane patches that also contained INa was significantly higher than the density of IIK or IK in membrane patches without INa. Sites of ACh receptor localization at nerve-muscle contacts, identified by labelling with rhodamine-alpha-bungarotoxin, were also found to contain both INa (4/5 cells) and IIK (5/5 cells). These results suggest that in Xenopus muscle cells in culture the channels mediating IIK along with sodium channels are clustered at sites of nerve contact and synaptic specializations.

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Section: Resultsmentioning

confidence: 97%

Localization of sodium and potassium currents at sites of nerve-muscle contact in embryonic Xenopus muscle cells in culture

Fry¹,

Moody-Corbett²

1999

Pfl�gers Archiv European Journal of Physiology

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Time Course of Ion Channel Development inXenopusMuscle Inducedin Vitroby Activin

Currie

Moody

1999

Developmental Biology

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During the process of mesoderm specification in Xenopus embryos, cells of the equatorial region are induced to form mesoderm in response to signals from the underlying endodermal cells. One mesodermal cell type resulting from this in vivo induction is skeletal muscle, which has a very specific and tightly regulated course of electrical and morphological development. Previously, electrical development could be analyzed only after neurulation, once myocytes could be morphologically identified. In vitro, activin triggers a cascade of events leading to the development of specific mesodermal tissues, including skeletal muscle; however, the precise role of activin in vivo is less clear. Much is now known about the mechanism and control of activin action, but very little is known about the subsequent time course of differentiation of activin-induced muscle. Such muscle is routinely identified by the presence of a small number of specific markers which, although they accurately confirm the presence of muscle, give little indication of the time course or quantitative aspects of muscle development. One of the most important functional aspects of muscle development is the acquisition of the complex electrical properties which allow it to function normally. Here we assess the ability of activin to drive in vitro the normal highly regulated sequence of electrical development in skeletal muscle. We find that in most, but not all, respects the normal time course of development of voltage-gated ion currents is well reproduced in activin-induced muscle. This characterization strengthens the case for activin as an agent capable of inducing the detailed developmental program of muscle and now allows for analysis of the regulation of electrical development prior to neurulation.

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Modifications of current properties by expression of a foreign potassium channel gene in Xenopus embryonic cells

Spruce

Moody

1995

J. Membarin Biol.

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The development of excitable cells is characterized by highly organized patterns of expression of ion channels. During the terminal differentiation of Xenopus muscle somites, potassium currents are expressed first just after Stage 15 (early-mid neurula), following a long period during which no voltage-dependent currents can be detected in any cell in the dorsal embryo. We have investigated whether early expression of a foreign delayed rectifier potassium channel may affect this endogenous pattern of electrical development. We injected the purified cRNA of the mammalian brain Shaker-like potassium channel, Kv1.1, into fertilized Xenopus eggs. The resulting currents were analyzed in blastomeres during a 12-hr period prior to Stage 15 and in differentiating muscle cells after Stage 15. In injected embryos, a high fraction of blastomeres expressed a delayed rectifier-type current. The Kv1.1 current could be distinguished from the endogenous muscle delayed potassium current (IK,X) by its very different voltage dependence. Separation of currents based on this difference indicated that, in injected embryos, IK,X appeared much earlier in development than in control embryos. Furthermore, even in cells which expressed solely Kv1.1-type current, the sensitivity of the current to dendrotoxin declined dramatically during development, approaching that of IK,X. These data suggest an interaction between Kv1.1 and endogenous channel subunits, and/or modification of the Kv1.1 protein by the embryonic cells in ways not seen in Xenopus oocytes or mammalian cell lines.

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Calcium current in embryonic Xenopus muscle cells in culture

Cited by 14 publications

References 13 publications

Localization of sodium and potassium currents at sites of nerve-muscle contact in embryonic Xenopus muscle cells in culture

Localization of sodium and potassium currents at sites of nerve-muscle contact in embryonic Xenopus muscle cells in culture

Time Course of Ion Channel Development inXenopusMuscle Inducedin Vitroby Activin

Modifications of current properties by expression of a foreign potassium channel gene in Xenopus embryonic cells

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