Renal chemosensitive and mechanosensitive afferent responses are preserved in TRPV1 knockout rats

Abstract

The transient receptor potential vanilloid type‐1 (TRPV1) channel is expressed in renal sensory nerves, and intrarenal administration of the TRPV1 agonist capsaicin increases renal afferent nerve activity (ARNA). Nonselective denervation of renal sensory nerves using high concentration capsaicin reduces arterial blood pressure (ABP) in experimental models of hypertension. Pharmacological blockade of TRPV1 using renal pelvic infusion of capsazepine attenuates ARNA responses to capsaicin, CGRP, and elevated pelvic pressure. Thus, TRPV1 channels mediate activation of renal sensory nerves.To test this hypothesis, we generated a novel TRPV1 knockout rat (TRPV1‐/‐) using CRISPR/Cas9 to produce a 26bp deletion in exon 3. Multifiber ARNA responses to chemical (bradykinin and capsaicin) and mechanical (elevated renal pelvic pressure) stimuli were compared in Inactin‐anesthetized male and female wild‐type and TRPV1‐/‐ littermates (250‐400g). There were no significant differences in baseline mean ABP between wild‐type and TRPV1‐/‐ rats (122±2 mmHg vs 122±3 mmHg, respectively; p=0.48, n=8‐10), or baseline ARNA between wild‐type and TRPV1‐/‐ rats (14±3 Hz vs 18±5 Hz, respectively; p=0.24, n=8‐10).Intrarenal artery infusion of capsaicin (0.1–10μM, 50μL per 15s) significantly increased ipsilateral ARNA in wild‐type but not TRPV1‐/‐ rats (Δ discharge 65±14 Hz vs 9±3 Hz at 10μM, respectively; p<0.05, n=7). As a second chemosensitive stimulus, intrarenal artery infusion of bradykinin (0.1–10μM, 50μL per 15s) produced significant increases in ARNA in ­both wild‐type and TRPV1‐/‐ rats that were not significantly different between groups (Δ discharge of 10μM: 52±11 Hz vs 76±21 Hz, respectively; p=0.33, n=7). Elevated renal pelvic pressure (0–20mmHg; 30s) significantly increased ARNA in both wild‐type and TRPV1‐/‐ rats; however, ARNA responses were significantly smaller in wild‐type versus TRPV1‐/‐ rats (Δ discharge with 20mmHg: 17±3 Hz versus 29±6 Hz, respectively; p=0.03, n=8‐9).The preservation of ARNA responses in TRPV1‐/‐ rats contradicts prior studies using pharmacological TRPV1 antagonists. A final set of experiments tested whether intrapelvic capsazepine infusion (200μM, 200μl per 3 min) attenuates ARNA responses to elevated pelvic pressure (20mmHg) in both wild‐type and Trpv1‐/‐ rats. Interestingly, pelvic administration of capsazepine attenuated mechanosensitive ARNA responses in both wildtype (saline: 31±3 Hz vs capsazepine: 8±1 Hz; n=3) and TRPV1‐/‐ (saline: 20±7 Hz vs capsazepine: 6±1 Hz; n=3) rats thereby suggesting a TRPV1‐independent action of capsazepine.In conclusion, TRPV1 channels are dispensable for the activation of chemo‐ and mechanosensitive renal sensory nerves.