Ca2+ regulation in the near-membrane microenvironment in smooth muscle cells.
The microenvironment between the plasma membrane and the near-membrane sarcoplasmic reticulum (SR) may play an important role in Ca(2+) regulation in smooth muscle cells. We used a three-dimensional mathematical model of Ca(2+) diffusion and regulation and experimental measurements of SR Ca(2+) uptake and the distribution of the SR in isolated smooth muscle cells to predict the extent that the near-membrane SR could load Ca(2+) after the opening of single plasma membrane Ca(2+) channels. We also modeled the effect of SR uptake on 1), single-channel Ca(2+) transients in the near-membrane space; 2), the association of Ca(2+) with Ca(2+) buffers in this space; and 3), the amount of Ca(2+) reaching the central cytoplasm of the cell. Our results indicate that, although single-channel Ca(2+) transients could increase SR Ca(2+) to a certain extent, SR Ca(2+) uptake is not rapid enough to greatly affect the magnitude of these transients or their spread to the central cytoplasm unless the Ca(2+) uptake rate of the peripheral SR is an order-of-magnitude higher than the mean rate derived from our experiments. Immunofluorescence imaging, however, did not reveal obvious differences in the density of SR Ca(2+) pumps or phospholamban between the peripheral and central SR in smooth muscle cells.
Bazzazi
Hojjat
H
Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada.
Kargacin
Margaret E
ME
Kargacin
Gary J
GJ
D000465:Algorithms; D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004058:Diffusion; D005753:Gastric Mucosa / Q000378:metabolism; D008856:Microscopy, Fluorescence; D015233:Models, Statistical; D009130:Muscle, Smooth / Q000166:cytology*; D011817:Rabbits; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D012503:Saponins / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013997:Time Factors; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D011994:Recombinant Proteins; D012503:Saponins; D000099211:Phospholamban