Requirement of potassium for the action of anti-diuretic hormone (ADH) on frog skin

The aim of the present study is to study whether the presence of K ⁺ in bathing media is required for the action of ADH to the ionic transport across the skin in the frog species Rana hexadactyla. lonic transport was measured as transepithelial potential difference (TEPD) and short circuit current (SCC) by using an indigenously developed computer based voltage-clamp technique. Addition of ADH (40 nM) on the serosal side significantly increased the TEPD and SCC with Normal Ringer (NR) on both sides. ADH had no effect subsequent to amiloride (100 M) pre-treatment, which confirmed the ADH-induced Na ⁺ transport. Chloride also has a significant role in the development of TEPD. To determine the role of K ⁺, Potassium-free Ringer (KFR) was placed on both sides; addition of ADH had no effect consequently. Further experiments were carried out to find out which side of K ⁺ was required for the action of ADH. There was a lack of ADH effect with apical NR and serosal KFR, demonstrating that serosal K ⁺ is essential to activate Na ⁺, K ⁺- ATPase. Similarly, the ADH effect was lacking with apical KFR and serosal NR that was the novel finding of this study. Due to the concentration gradient, the K ⁺ was secreted from serosal side to apical side through barium (1 mM) blockable K ⁺ channel. This study provides evidence that serosal as well as apical K ⁺ are necessary for the action of ADH.