Mechanisms underlying regional differences in the Ca2+ sensitivity of BK(Ca) current in arteriolar smooth muscle.
J Physiol
; 591(5): 1277-93, 2013 Mar 01.
Article
em En
| MEDLINE
| ID: mdl-23297302
ABSTRACT
Abstract ß1-Subunits enhance the gating properties of large-conductance Ca(2+)-activated K(+) channels (BKCa) formed by α-subunits. In arterial vascular smooth muscle cells (VSMCs), ß1-subunits are vital in coupling SR-generated Ca(2+) sparks to BKCa activation, affecting contractility and blood pressure. Studies in cremaster and cerebral VSMCs show heterogeneity of BKCa activity due to apparent differences in the functional ß1-subunitα-subunit ratio. To define these differences, studies were conducted at the single-channel level while siRNA was used to manipulate specific subunit expression. ß1 modulation of the α-subunit Ca(2+) sensitivity was studied using patch-clamp techniques. BKCa channel normalized open probability (NPo) versus membrane potential (Vm) curves were more left-shifted in cerebral versus cremaster VSMCs as cytoplasmic Ca(2+) was raised from 0.5 to 100 µm. Calculated V1/2 values of channel activation decreased from 72.0 ± 6.1 at 0.5 µm Ca(2+)i to -89 ± 9 mV at 100 µm Ca(2+)i in cerebral compared with 101 ± 10 to -63 ± 7 mV in cremaster VSMCs. Cremaster BKCa channels thus demonstrated an â¼2.5-fold weaker apparent Ca(2+) sensitivity such that at a value of Vm of -30 mV, a mean value of [Ca(2+)]i of 39 µm was required to open half of the channels in cremaster versus 16 µm [Ca(2+)]i in cerebral VSMCs. Further, shortened mean open and longer mean closed times were evident in BKCa channel events from cremaster VSMCs at either -30 or 30 mV at any given [Ca(2+)]. ß1-Subunit-directed siRNA decreased both the apparent Ca(2+) sensitivity of BKCa in cerebral VSMCs and the appearance of spontaneous transient outward currents. The data are consistent with a higher ratio of ß1-subunitα-subunit of BKCa channels in cerebral compared with cremaster VSMCs. Functionally, this leads both to higher Ca(2+) sensitivity and NPo for BKCa channels in the cerebral vasculature relative to that of skeletal muscle.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Encéfalo
/
Ativação do Canal Iônico
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Cálcio
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Músculo Esquelético
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Miócitos de Músculo Liso
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Canais de Potássio Ativados por Cálcio de Condutância Alta
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Músculo Liso Vascular
Tipo de estudo:
Diagnostic_studies
Limite:
Animals
Idioma:
En
Ano de publicação:
2013
Tipo de documento:
Article