Figure 10.

Changes of ENaC activity by acute increases of [Na⁺]_i is isoform dependent. Oocytes were injected with 25 mM Na⁺ as described in text. Amiloride sensitive conductance was recorded at −100 mV and normalized to that immediately before Na⁺ injection. (A) Changes in α₆₆₉βγ or α₇₂₈βγ expressing oocytes studied in high [Na⁺] in response to an increase of [Na⁺]_i from 65 to 90 mM. (B) Changes in α₆₆₉βγ or α₇₂₈βγ expressing oocytes studied in low [Na⁺] in response to an increase of [Na⁺]_i from 12 to 37 mM. The two α isoforms displayed marked differences indicating higher sensitivity of α₆₆₉ to changes of [Na⁺]_i from a low baseline. Together these data indicate that inhibition of α₇₂₈ by increasing Na⁺ occurs at [Na⁺]_i > 37 mM making this isoform different in the way it responds to Na⁺ than α₆₆₉. (n = 6 in each group). P < 0.05 for the time dependent differences between the 2 isoforms except the ending points (last 2) in (B).