ISSN:
1432-2013
Keywords:
Smooth Muscle
;
Calcium Distribution
;
Lanthanum
;
D600
;
Excitation-Concentration Coupling
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The calcium distribution in smooth muscle cells of the taenia coli has been studied with a method based on the action of lanthanum ions. La3+-ions make it possible to separate the extracellular calcium from the cellular calcium by their high affinity for extracellular calcium binding sites and by their blocking action on the transmembrane calcium movements. Using this method the cellular calcium content and its exchangeable fraction have been determined. In spontaneously active tissues the exchange of the cellular calcium reaches a maximal value of 108 μM/kg wet wt or 1/6 of the total cellular calcium, while in quiescent tissues (treated with D600) this maximal value is 80 μM/kg wet wt. During K depolarization a large amount of extracellular calcium penetrates in the cellular compartment. This entry and the corresponding tension development are inhibited by D600. These results are interpreted by assuming that even during spike discharge the Ca-permeability of the membrane is very small and that this entering calcium could function as a trigger, releasing intracellularly localized calcium. This physiological mechanism should be distinguished from the important uptake of calcium occurring during K-depolarization.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00586650
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