McCarron, J. G., Olson, M. L., Currie, S., Wright, A. J., Anderson, K.I. and Girkin, J. M. (2009) Elevations of intracellular calcium reflect normal voltage-dependent behavior, and not constitutive activity, of voltage-dependent calcium channels in gastrointestinal and vascular smooth muscle. Journal of General Physiology, 133(4), pp. 439-457. (doi: 10.1085/jgp.200810189)
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Publisher's URL: http://dx.doi.org/10.1085/jgp.200810189
Abstract
In smooth muscle, the gating of dihydropyridine-sensitive Ca2+ channels may either be stochastic and voltage dependent or coordinated among channels and constitutively active. Each form of gating has been proposed to be largely responsible for Ca2+ influx and determining the bulk average cytoplasmic Ca2+ concentration. Here, the contribution of voltage-dependent and constitutively active channel behavior to Ca2+ signaling has been studied in voltage-clamped single vascular and gastrointestinal smooth muscle cells using wide-field epifluorescence with near simultaneous total internal reflection fluorescence microscopy. Depolarization (-70 to + 10 mV) activated a dihydropyridine-sensitive voltage-dependent Ca2+ current (I-Ca) and evoked a rise in [Ca2+] in each of the subplasma membrane space and bulk cytoplasm. In various regions of the bulk cytoplasm the [Ca2+] increase ([Ca2+](c)) was approximately uniform, whereas that of the subplasma membrane space ([Ca2+](PM)) had a wide range of amplitudes and time courses. The variations that occurred in the subplasma membrane space presumably reflected an uneven distribution of active Ca2+ channels (clusters) across the sarcolemma, and their activation appeared consistent with normal voltage-dependent behavior. Indeed, in the present study, dihydropyridine-sensitive Ca2+ channels were not normally constitutively active. The repetitive localized [Ca2+](PM) rises ("persistent Ca2+ sparklets") that characterize constitutively active channels were observed rarely (2 of 306 cells). Neither did dihydropyridine-sensitive constitutively active Ca2+ channels regulate the bulk average [Ca2+](c). A dihydropyridine blocker of Ca2+ channels, nimodipine, which blocked I-Ca and accompanying [Ca2+](c) rise, reduced neither the resting bulk average [Ca2+](c) (at - 70 mV) nor the rise in [Ca2+](c), which accompanied an increased electrochemical driving force on the ion by hyperpolarization (-130 mV). Activation of protein kinase C with indolactam-V did not induce constitutive channel activity. Thus, although voltage-dependent Ca2+ channels appear clustered in certain regions of the plasma membrane, constitutive activity is unlikely to play a major role in [Ca2+](c) regulation. The stochastic, voltage-dependent activity of the channel provides the major mechanism to generate rises in [Ca2+].
Item Type: | Articles |
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Status: | Published |
Refereed: | Yes |
Glasgow Author(s) Enlighten ID: | Anderson, Professor Kurt |
Authors: | McCarron, J. G., Olson, M. L., Currie, S., Wright, A. J., Anderson, K.I., and Girkin, J. M. |
College/School: | College of Medical Veterinary and Life Sciences > School of Cancer Sciences |
Journal Name: | Journal of General Physiology |
Journal Abbr.: | JGP |
Publisher: | Rockefeller University Press |
ISSN: | 0022-1295 |
ISSN (Online): | 1540-7748 |
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