Yanagi N, Maruyama T, Arita M, Kaji Y, Niho Y. Alterations in electrical and mechanical activity in Langendorff-perfused guinea pig hearts exposed to decreased external sodium concentration with or without hypotonic insult.
PATHOPHYSIOLOGY : THE OFFICIAL JOURNAL OF THE INTERNATIONAL SOCIETY FOR PATHOPHYSIOLOGY 2001;
7:251-261. [PMID:
11228395 DOI:
10.1016/s0928-4680(00)00056-0]
[Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In order to examine electrical and mechanical effects of hyponatremia and hypotonicity, relevant to those in patients with 'water intoxication' syndrome, Langendorff-perfused guinea pig hearts were exposed to reduced NaCl concentrations (hypotonic [NaCl](0)-reduction) under the monitoring of left ventricular developed pressure (LVDP) and epicardial ECG. In some hearts, hyponatremia (from 140 to 80 mEq/l) was compensated for by adding mannitol to maintain osmolarity at a constant level (isotonic [NaCl](0)-reduction) or tetraethylammonium chloride to maintain both osmolarity and chloride concentrations at a constant level (isotonic [Na(+)](0)-reduction). Progressive isotonic [NaCl](0)-reduction increased LVDP, which was abolished in the presence of KB-R7943, a novel inhibitor of Na(+)/Ca(2+)-exchange. LVDP was reduced in hypotonic [NaCl](0)-reduction in which myocardial water content was increased. PQ interval and QRS duration were prolonged with both hypotonic and isotonic [NaCl](0)-reduction and these changes tended to be more pronounced with hypotonic than with isotonic [NaCl](0)-reduction. Similar ECG changes were also evident with isotonic [Na(+)](0)-reduction. Gd(3+) (1-5 µM), a blocker of stretch-activated nonspecific cation channels, had no substantial effects on the electrical or mechanical changes seen with hypotonic [NaCl](0)-reduction. In conclusion, isotonic [NaCl](0)-reduction produced a positive inotropism by modulating Na(+)/Ca(2+)-exchange, whereas hypotonic [NaCl](0)-reduction led to negative inotropism, due in part to hypotonic myocardial swelling. In addition, [Na(+)](0)-reduction, irrespective of the concomitant [Cl(-)](0) or osmotic changes, depressed atrioventricular as well as intraventricular conduction.
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