Ca²⁺-reabsorption function of the perfused rat cauda epididymis. (A) Ca²⁺ reabsorption by the rat cauda epididymis when perfused with 1 mM Ca²⁺-containing bicarbonate (HCO₃)- or HEPES-buffered Krebs solution at pH 7.4. (B) The rate of Ca²⁺ reabsorption by the rat corpus epididymis was significantly higher at a higher concentration of luminal Ca²⁺ (2 mM) versus that at a low Ca²⁺ concentration (0.5 mM). (C and D) Time profile showing the reversible inhibition effect of ruthenium red (100 µM) on the rate of Ca²⁺ reabsorption by the rat cauda epididymis. The solution was HEPES-buffered Krebs at pH 7.4. The calculated error bar was within the data point. (E) Dose-dependent inhibition relationship of ruthenium red on Ca²⁺ reabsorption. (F) The rate of Ca²⁺ reabsorption by the rat cauda epididymis was slightly attenuated by changing the perfusing solution from pH 7.4 to 6.8, but it was slightly enhanced when the pH was changed to 8.2. The pH of the solution was buffered with HEPES (n = 5 rats per point). The dotted line indicates the zero current levels. Error bars represent SEM.