Diminished paracrine regulation of the epithelial Na⁺ channel by purinergic signaling in mice lacking connexin 30

We tested whether ATP release through Connexin 30 (Cx30) is part of a local purinergic regulatory system intrinsic to the aldosterone-sensitive distal nephron (ASDN) important for proper control of sodium excretion; if changes in sodium intake influence ATP release via Cx30; and if this allows a normal ENaC response to changes in systemic sodium levels. In addition, we define the consequences of disrupting ATP regulation of ENaC in Cx30^-/- mice. Urinary ATP levels in wildtype mice increase with sodium intake, being lower and less dependent on sodium intake in Cx30^-/- mice. Loss of inhibitory ATP regulation causes ENaC activity to be greater in Cx30^-/- versus wild-type mice, particularly with high sodium intake. This results from compromised ATP release rather than end-organ resistance: ENaC in Cx30 ^-/- mice responds to exogenous ATP. Thus, loss of paracrine ATP feedback regulation of ENaC in Cx30^-/- mice disrupts normal responses to changes in sodium intake. Consequently, ENaC is hyperactive in Cx30 ^-/- mice lowering sodium excretion particularly during increases in sodium intake. Clamping mineralocorticoids high in Cx30^-/- mice fed a high sodium diet causes a marked decline in renal sodium excretion. This is not the case in wild-type mice, which are capable of undergoing aldosterone-escape. This loss of the ability of ENaC to respond to changes in sodium levels contributes to salt-sensitive hypertension in Cx30^-/- mice.