Key result
Perfusion of rabbit intraventricular septum with 200 mM sodium caused an initial 20.4% fall in dP/dt followed by recovery, correlating with sodium uptake and suggesting a Na-Ca exchange system.
High extracellular sodium induces a transient decrease in myocardial contractility followed by recovery, likely mediated by a Na-Ca exchange system that enhances Ca influx in response to increased intracellular Na.
Rabbit septal data should not inform clinical sodium use; leaves open Na-Ca exchange mechanisms in contractility.
The effects of an extracellular sodium (Na) concentration of 200 m M on function, ionic exchange, and water movements were examined in the vascularly perfused rabbit intraventricular septum. When the perfusate was switched from 1.42 m M Na to 200 m M Na, dP/dt fell 20.4% over 2 minutes; dP/dt then recovered to the control level. The time course of the functional recovery correlated with the uptake of Na into the slowly exchangeable fraction of the tissue, and the rate of recovery in 200 m M Na depended on the frequency of contraction of the preparation. During perfusion with 200 m M Na, a 41% increase in slow-phase Na content compared with the content during perfusion with 142 m M Na was observed. The hyperosmolar perfusate induced a 21% cellular dehydration within 10 minutes as estimated from measurement of 10-minute 35 SO 4 space and total tissue water. The time course of dehydration was much more rapid than the time course of functional recovery. Calcium (Ca) influx during the period when dP/dt had returned to control levels in 200 m M Na was the same as it was during a control period in 1.42 m M Na. Thus, there appears to be a Na-Ca exchange system which enhances Ca influx and thus causes an inotropic effect in response to an increase in intracellular Na concentration.
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TILLISCH et al. (1974) studied this question. Extracellular sodium concentration of 200 mM vs. 1.42 mM / 142 mM sodium perfusate was evaluated on dP/dt, ionic exchange, and water movements. Perfusion of rabbit intraventricular septum with 200 mM sodium caused an initial 20.4% fall in dP/dt followed by recovery, correlating with sodium uptake and suggesting a Na-Ca exchange system.
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