TRPV1 activation stimulates NKCC1 and increases hydrostatic pressure in mouse lens.

The porcine lens response to a hyperosmotic stimulus involves an increase in the activity of NKCC1. Recent studies with agonists and antagonists pointed to a mechanism that appears to depend on activation of TRPV1. Here we compare responses in lenses and cultured lens epithelium obtained from TRPV1(-/-) and wild type (WT) mice. Hydrostatic pressure (HP) in lens surface cells was determined using a manometer-coupled microelectrode approach. The TRPV1 agonist capsaicin caused a transient HP increase in WT lenses that peaked after ~30 min then returned toward baseline. TRPV1(-/-) lenses did not respond to capsaicin. The NKCC inhibitor bumetanide prevented the HP response to capsaicin in WT lenses. Potassium transport was examined by measuring Rb(+) uptake. Capsaicin increased Rb(+) uptake in WT but not in TRPV1(-/-) cells. Bumetanide, A889425 and the Akt inhibitor Akti prevented the Rb(+) uptake response to capsaicin. The bumetanide-sensitive component of Rb(+) uptake more than doubled in response to capsaicin. Capsaicin also elicited rapid (<2 min) NKCC1 phosphorylation in WT but not TRPV1(-/-) cells. HP recovery was absent in TRPV1(-/-) lenses exposed to hyperosmotic solution. Bumetanide and Akti prevented HP recovery in WT lenses exposed to hyperosmotic solution. Taken together, responses to capsaicin and hyperosmotic solution point to a functional role for TRPV1 channels in mouse lens. Lack of NKCC1 phosphorylation and Rb(+) uptake responses in TRPV1(-/-) epithelium reinforces that a hyperosmotic challenge causes TRPV1-dependent NKCC1 activation. The results are consistent with a role for the TRPV1-activated signaling pathway leading to NKCC1 stimulation in lens osmotic homeostasis.