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Effects of divalent and trivalent cations on Na+-Ca2+ exchange in cardiac sarcolemmal vesicles
Abstract:
Inhibition of Na+-Ca2+ exchange processes in canine cardiac sarcolemmal vesicles by several divalent and trivalent cations has been investigated. The order of cation effectiveness in inhibiting initial rates of Nai+-induced Ca2+ uptake in the presence of 140 mM Nai+ and 20 microM Cao2+ is La3+ greater than Nd3+ greater than Tm3+ approximately Y3+ greater than Cd2+ much greater than Sr2+ greater than Ba2+ approximately Mn2+ much greater than Mg2+. The effectiveness of the divalent ions is related to their ionic crystal radius as compared with that of Ca2+. No such relationship was observed for the trivalent ions, which appeared instead to be more effective the larger their radius. Very low concentrations of trivalent ions ((1-6).10(-7)M) caused slight stimulation of Ca2+-exchange uptake. The trivalent ions also inhibited passive and Nao+-induced Ca2+ efflux from sarcolemmal vesicles, in the same concentration range as that for inhibiting uptake. The divalent ions, however, stimulated Ca2+ efflux, possibly via divalent cation-Ca2+ exchange. These various results suggest that the divalent and trivalent cations interact differently with the exchange apparatus in the sarcolemma.
Insights
Divalent and trivalent cations inhibit sodium-calcium exchange in cardiac sarcolemma differently. Trivalent cations are more effective inhibitors, while divalent cations can stimulate calcium efflux, suggesting distinct interactions with the sarcolemmal exchange apparatus.
Area of Science:
- Cardiovascular Physiology
- Membrane Transport
- Biochemistry
Background:
- The Na+-Ca2+ exchanger is crucial for cardiac function, regulating intracellular calcium.
- Understanding how various cations affect this exchanger is vital for cardiovascular research.
Purpose of the Study:
- To investigate the inhibitory effects of divalent and trivalent cations on Na+-Ca2+ exchange in canine cardiac sarcolemmal vesicles.
- To elucidate the differential mechanisms by which these cations interact with the sarcolemmal exchange apparatus.
Main Methods:
- Utilized canine cardiac sarcolemmal vesicles to study Na+-Ca2+ exchange.
- Measured initial rates of Na+-induced Ca2+ uptake and Ca2+ efflux.
- Investigated the effects of various divalent (Cd2+, Sr2+, Ba2+, Mn2+, Mg2+) and trivalent (La3+, Nd3+, Tm3+, Y3+) cations.
Main Results:
- Cation effectiveness in inhibiting Na+-induced Ca2+ uptake followed the order: La3+ > Nd3+ > Tm3+ ≈ Y3+ > Cd2+ > Sr2+ > Ba2+ ≈ Mn2+ > Mg2+.
- Divalent ion effectiveness correlated with ionic crystal radius, unlike trivalent ions, which showed increased effectiveness with larger radii.
- Trivalent ions at low concentrations stimulated Ca2+ uptake and inhibited Ca2+ efflux, while divalent ions stimulated Ca2+ efflux.
Conclusions:
- Divalent and trivalent cations exhibit distinct interaction patterns with the sarcolemmal Na+-Ca2+ exchange mechanism.
- The findings suggest different binding sites or modes of action for these cation types on the sarcolemma.