title: Ca2+ transport systems mediating the high K+/low Na+-induced uptake of Ca2+ into rat atrium.
abstract: The effect of high K+/low Na+-Tyrode's solution on Ca2+ uptake into neonatal rat atrium was studied using 45Ca2+. Substitution of 60-129 mM Na+ in Tyrode's solution by equimolar concentrations of K+ or choline, significantly (with the exception of 60 mM choline substitution) increased Ca2+ uptake above control. Furthermore, the Ca2+ uptake stimulated by K+ substitution was significantly greater than that stimulated by choline substitution at the corresponding concentrations. The choline/low Na+-induced Ca2+ uptake (i.e. that above the Ca2+ uptake measured in normal Tyrode's solution) was increased by pre-exposure to either ice-cold Tyrode's solution for 1 h (approximately 36% increase) or to K+-free Tyrode's solution for 3 h (approximately 100% increase). The choline/low Na+-induced Ca2+ uptake was abolished by the hypertonic addition of NaCl (returning the bathing Na+ concentration to normal), increased (approximately 140%) by the addition of 1.8 mM PO4(3-)-free Hepes buffered choline/low Na+ media, but unaffected by 0.2 mM cadmium. The high K+/low Na+-induced Ca2+ uptake (i.e. that above the Ca2+ uptake measured in normal Tyrode's solution) was relatively insensitive to pre-exposure to cold (0% change) or K+-free media (11% increase) and only 50% inhibited by the hypertonic addition of NaCl (returning the bathing Na+ concentration to normal). However, the high K+/low Na+-induced Ca2+ uptake was 57% inhibited by 0.2 mM cadmium and approximately 30% inhibited by the addition of 1.8 mM PO4(3-) to HCO3-/PO4(3-)-free Hepes buffered high K+/low Na+ media.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001692:Biological Transport; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002794:Choline / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D010710:Phosphates / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D012964:Sodium / Q000494:pharmacology*; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D010710:Phosphates; D002104:Cadmium; D012965:Sodium Chloride; D012964:Sodium; D004110:Diltiazem; D007545:Isoproterenol; D002794:Choline; D011188:Potassium; D002118:Calcium