Competitive membrane adsorption of Na+, K+, and Ca2+ in smooth muscle cells.
A theory for Na+, K+ and Ca2+ competitive adsorption to a charged membrane is used to explain a number of experimental observations in smooth muscle. Adsorption is described by Langmuir isotherms for mono- and divalent cations which in turn are coupled in a self-consistent way to the bulk solution through the diffuse double layer theory and the Boltzman equations. We found that the dissociation constants for binding of Na+, K+ and Ca2+ in guinea pig taenia coli are ca. 0.009, 1.0, and 4 X 10(-8) M, respectively. Furthermore, the effect of a Ca2+ pump that maintains free surface Ca2+ concentration constant is investigated. A decrease in intracellular Na+ content results in an increased Ca2+ uptake; part of this uptake is due to an increase in surface-bound Ca2+ in an intracellular compartment which is in contact with the myofilaments. Variations in the amount of charge available to bind Ca2+ and the surface charge density are studied and their effect interpreted in terms of different pharmacological agents.
D000327:Adsorption; D001667:Binding, Competitive; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D008954:Models, Biological; D009130:Muscle, Smooth / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D012964:Sodium; D011188:Potassium; D002118:Calcium