Figure 5. Resting Na⁺ influx in rabbit and rat myocytes.

A, representative experiment in a rabbit cell. Na⁺ influx was calculated as the slope of the initial increase in [Na⁺]_i following abrupt pump inhibition with K⁺-free solution. Na⁺,K⁺-ATPase was blocked in the absence or presence of various inhibitors of Na⁺ entry (30 μm TTX in this case). B, average data for rabbit and rat myocytes. Shown are the total influx (Control) and the influx measured in the presence of 30 μm TTX (to block Na⁺ channels), 2 μm HOE 642 (to block Na⁺/H⁺ exchange), 5 mm Ni²⁺ (to block NCX), and also in the presence of all three blockers together (All). *P < 0.05 in rat vs. rabbit. C, TTX-, HOE 642- and Ni²⁺-sensitive Na⁺ influx (estimated as the difference between the total resting influx and the influx measured in the presence of the respective drug).