NDLI: Nifedipine blocks Ca2+ store refilling through a pathway not involving L-type Ca2+ channels in rabbit arteriolar smooth muscle

Content Provider	PubMed Central
Author	Curtis, Tim M. Scholfield, C. Norman
Copyright Year	2001
Abstract	This study assessed the contribution of L-type Ca2+ channels and other Ca2+ entry pathways to Ca2+ store refilling in choroidal arteriolar smooth muscle. Voltage-clamp recordings were made from enzymatically isolated choroidal microvascular smooth muscle cells and from cells within vessel fragments (containing < 10 cells) using the whole-cell perforated patch-clamp technique. Cell Ca2+ was estimated by fura-2 microfluorimetry. After Ca2+ store depletion with caffeine (10 mm), refilling was slower in cells held at -20 mV compared to -80 mV (refilling half-time was 38 ± 10 and 20 ± 6 s, respectively). To attempt faster refilling via L-type Ca2+ channels, depolarising steps from -60 to -20 mV were applied during a 30 s refilling period following caffeine depletion. Each step activated L-type Ca2+ currents and [Ca2+]i transients, but failed to accelerate refilling. At -80 mV and in 20 mm TEA, prolonged caffeine exposure produced a transient Ca2+-activated Cl− current (I Cl(Ca)) followed by a smaller sustained current. The sustained current was resistant to anthracene-9-carboxylic acid (1 mm; an I Cl(Ca) blocker) and to BAPTA AM, but was abolished by 1 μm nifedipine. This nifedipine-sensitive current reversed at +29 ± 2 mV, which shifted to +7 ± 5 mV in Ca2+-free solution. Cyclopiazonic acid (20 μm; an inhibitor of sarcoplasmic reticulum Ca2+-ATPase) also activated the nifedipine-sensitive sustained current. At -80 mV, a 5 s caffeine exposure emptied Ca2+ stores and elicited a transient I Cl(Ca). After 80 s refilling, another caffeine challenge produced a similar inward current. Nifedipine (1 μm) during refilling reduced the caffeine-activated I Cl(Ca) by 38 ± 5 %. The effect was concentration dependent (1-3000 nm, EC50 64 nm). In Ca2+-free solution, store refilling was similarly depressed (by 46 ± 6 %). Endothelin-1 (10 nm) applied at -80 mV increased [Ca2+]i, which subsided to a sustained 198 ± 28 nm above basal. Cell Ca2+ was then lowered by 1 μm nifedipine (to 135 ± 22 nm), which reversed on washout. These results show that L-type Ca2+ channels fail to contribute to Ca2+ store refilling in choroidal arteriolar smooth muscle. Instead, they refill via a novel non-selective store-operated cation conductance that is blocked by nifedipine.
Related Links	http://dx.doi.org/10.1111/j.1469-7793.2001.0609e.x
Starting Page	609
File Format	PDF
ISSN	14697793
e-ISSN	14697793
Journal	The Journal of Physiology
Issue Number	Pt 3
Volume Number	532
Language	English
Publisher	Blackwell Science Inc
Publisher Date	2001-05-01
Access Restriction	Open
Rights Holder	Blackwell Science Inc
Subject Keyword	Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Physiology Sports Science

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