Sensitivity to low pH in mouse glomus type I cells correlates with ASIC3 expression

Abstract

We have recently reported that acid‐sensing ion channels (ASICs) are expressed in glomus cells of rat carotid bodies (CB) and that their activation at low extracellular pH results in rapid early depolarization which is inhibited by amiloride (Circ Res 101:109‐1019, 2007). Moreover, the ASIC mediated inward current and depolarization at low pH are enhanced in glomus cells of spontaneously hypertensive rat (SHR) which overexpress ASIC3 in their carotid bodies (Circ Res 105:536‐545, 2010). In this study we tested the hypothesis that ASIC3 contributes to responses to low pH in mouse carotid bodies (CBs). We contrasted calcium transients Δ[Ca2+]i during extracellular acidosis (pH 6.0) and cyanide (CN 1mM) in three groups of mice: ASIC3 null (KO), wild type (WT), and ASIC3 transgenic (Tg) mice. Clusters of glomus cells were dissociated from the carotid bodies, loaded with Fluo4/AM (a single wavelength Ca2+ probe), imaged with a CCD camera (Photometrics Cool SNAP‐cf) and analyzed with software (MetaMorph 6.1). Baseline values [Ca2+]i were 57±2, 56±3, and 55±5 nM in KO, WT and Tg respectively. The results shown below indicate that in KO there was a significant reduction in the percentage of cells responding to low pH compared to CN. The magnitude of the Ca2+ transients during low pH was significantly lower than during CN in KO mice but significantly higher in Tg mice (p < 0.01). Low pH 6.0 CN (1mM) KO WT Tg KO WT Tg Total cells 207 205 32 118 129 32 % responsive 41%† 75% 69% 71% 81% 59% Δ[Ca2+]i nM 9±1* 10±1* 15±1†* 12±1 14±1 7±1 p < 0.05 (KO or Tg vs. WT); p < 0.01 (pH6.0 vs. CN) Contrasting responses to low pH to those with CN allowed us to confirm the specificity of the correlation between pH responsiveness and ASIC3 expression. The results indicate that ASIC3 is an important determinant of acid sensitivity in mouse carotid body chemoreceptors. (HL14388).