Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Schuhmann, K; Romanin, C; Baumgartner, W; Groschner, K.
Intracellular Ca2+ inhibits smooth muscle L-type Ca2+ channels by activation of protein phosphatase type 2B and by direct interaction with the channel.
J Gen Physiol. 1997; 110(5):503-513
Doi: 10.1085/jgp.110.5.503
[OPEN ACCESS]
Web of Science
PubMed
FullText
FullText_MUG
Google Scholar
- Führende Autor*innen der Med Uni Graz
- Groschner Klaus
- Altmetrics:
- Dimensions Citations:
- Plum Analytics:
- Scite (citation analytics):
- Abstract:
- Modulation of L-type Ca2+ channels by tonic elevation of cytoplasmic Ca2+ was investigated in intact cells and inside-out patches from human umbilical vein smooth muscle. Ba2+ was used as charge carrier, and run down of Ca2+ channel activity in inside-out patches was prevented with calpastatin plus ATP. Increasing cytoplasmic Ca2+ in intact cells by elevation of extracellular Ca2+ in the presence of the ionophore A23187 inhibited the activity of L-type Ca2+ channels in cell-attached patches. Measurement of the actual level of intracellular free Ca2+ with fura-2 revealed a 50% inhibitory concentration (IC50) of 260 nM and a Hill coefficient close to 4 for Ca2+- dependent inhibition. Ca2+-induced inhibition of Ca2+ channel activity in intact cells was due to a reduction of channel open probability and availability. Ca2+-induced inhibition was not affected by the protein kinase inhibitor H-7 (10 microM) or the cytoskeleton disruptive agent cytochalasin B (20 microM), but prevented by cyclosporin A (1 microg/ ml), an inhibitor of protein phosphatase 2B (calcineurin). Elevation of Ca2+ at the cytoplasmic side of inside-out patches inhibited Ca2+ channels with an IC50 of 2 microM and a Hill coefficient close to unity. Direct Ca2+-dependent inhibition in cell-free patches was due to a reduction of open probability, whereas availability was barely affected. Application of purified protein phosphatase 2B (12 U/ml) to the cytoplasmic side of inside-out patches at a free Ca2+ concentration of 1 microM inhibited Ca2+ channel open probability and availability. Elevation of cytoplasmic Ca2+ in the presence of PP2B, suppressed channel activity in inside-out patches with an IC50 of approximately 380 nM and a Hill coefficient of approximately 3; i.e., characteristics reminiscent of the Ca2+ sensitivity of Ca2+ channels in intact cells. Our results suggest that L-type Ca2+ channels of smooth muscle are controlled by two Ca2+-dependent negative feedback mechanisms. These mechanisms are based on (a) a protein phosphatase 2B-mediated dephosphorylation process, and (b) the interaction of intracellular Ca2+ with a single membrane-associated site that may reside on the channel protein itself.
- Find related publications in this database (using NLM MeSH Indexing)
- Calcineurin - metabolism
- Calcium - metabolism Calcium - physiology
- Calcium Channels - metabolism
- Cyclosporine - pharmacology
- Enzyme Activation - physiology
- Humans -
- Intracellular Membranes - metabolism
- Ion Channel Gating - physiology
- Muscle, Smooth, Vascular - drug effects Muscle, Smooth, Vascular - metabolism
- Patch-Clamp Techniques -
- Find related publications in this database (Keywords)
- L-type Ca2+ channels
- gating
- protein phosphatase 2B
- vascular smooth muscle
- patch clamp