Effects of antidiuretic hormone,parathyroid hormone and glucagon on transepithelial voltage and resistance of the cortical and medullary thick ascending limb of Henle's loop of the mouse nephron

The effect of antidiuretic hormone (arginine vasopressin, AVP, 10⁻¹⁰mol.l⁻¹), parathyroid hormone (PTH, 10⁻⁸ mol.l⁻⁸) and glucagon (10⁻⁸ mol.l⁻¹) on the transepithelial potential difference (PD_te) and the transepithelial resistance (R_te) were tested in in vitro perfused cortical (cTAL) and medullary (mTAL) thick ascending limbs of Henle's loop of the mouse nephron. When compared with mTAL segments (PD_te: 8.5±0.4 mV,n=16), cTAL segments displayed a high PD_te of 15.7±0.9 mV (n=11) at the beginning of perfusion experiments which reached a value of 9.4±0.6 mV (n =11) after 38±4 min perfusion. Simultaneously R_te increased significantly from 24±3 to 28±1 Ω cm² (n=11). When PTH, AVP or glucagon were added to the bath solution, PD_te increased with PTH from 10.3±0.8 to 15.2±0.8 mV (n=13), with AVP from 10.2±0.5 to 15.0±0.7 mV (n=24) and with glucagon from 11.3±1.9 to 15.3±2.1 mV (n=8). At the same time R_te decreased from 30±3 to 23±2 Ω cm², from 28±1 to 23±1 Ω cm² and from 23±2 to 18±2 Ω cm², respectively. In mTAL segments, AVP and glucagon increased PD_te from 8.4+0.5 to 13.5±0.9 mV (n=11) and from 8.8±0.6 to 12.8±0.6 mV (n=8) respectively, while R_te decreased significantly from 23±1 to 20±1 Ω cm² and from 27±3 to 21±3 Ω cm². PTH, on the other hand, had no effect on PD_te and R_te. Since the response to PTH appeared to be specific to cTAL segments, paired experiments were performed, in which AVP or glucagon were successively tested with PTH on cTAL and mTAL segments, to ascertain the specificity of the hormonal response. In cTAL segments, PTH and AVP increased the equivalent short-circuit current (I_sc=PD_te/R_te) by 82% and 86% respectively, while PTH and glucagon, in another series, increased I_sc by 95% and 81% respectively. In mTAL segments, I_sc was increased in the presence of AVP and glucagon by 88%, and 93% respectively, whereas PTH had no effect. These results indicate that Nacl reabsorption in cTAL segments is stimulated by AVP, PTH and glucagon and in mTAL segments by AVP and glucagon. The amplitude of the response to the hormones is similar in the two segments. The residual stimulation in cTAL segments, however, persists longer than in mTAL segments.