Altered myogenic vasoconstriction and regulation of whole kidney blood flow in the ASIC2 knockout mouse

Abstract

Previous studies from our laboratory have suggested that degenerin proteins contribute to myogenic constriction, a mechanism of blood flow regulation and protection against pressure-dependent organ injury, in renal vessels. The goal of the present study was to determine the importance of one family member, acid-sensing ion channel 2 (ASIC2), in myogenic constriction of renal interlobar arteries, myogenic regulation of whole kidney blood flow, renal injury, and blood pressure using ASIC2(+/+), ASIC2(+/-), and ASIC2(-/-) mice. Myogenic constriction in renal interlobar arteries was impaired in ASIC2(+/-) and ASIC2(-/-) mice, whereas constriction to KCl/phenylephrine was unchanged. Correction of whole kidney renal vascular resistance (RVR) during the first 5 s after a 10- to 20-mmHg step increase in perfusion pressure, a timeframe associated with myogenic-mediated correction of RVR, was slowed (4.2 ± 0.9, 0.3 ± 0.7, and 2.4 ± 0.3 resistance units/s in ASIC2(+/+), ASIC2(+/-), and ASIC2(-/-) mice). Although modest reductions in function were observed in ASIC2(-/-) mice, greater reductions were observed in ASIC2(+/-) mice, which may be explained by protein-protein interactions of ASIC2 with other degenerins. Isolated glomeruli from ASIC2(+/-) and ASIC2(-/-) mice had modest alterations in the expression of inflammation and injury markers (transforming growth factor-β, mouse anti-target of antiproliferative antibody-1, and nephrin), whereas ASIC2(+/-) mice had an increase in the remodeling marker collagen type III. Consistent with a more severe loss of function, mean arterial pressure was increased in ASIC2(+/-) mice (131 ± 3 mmHg) but not in ASIC2(-/-) mice (122 ± 3 vs. 117 ± 2 mmHg in ASIC2(+/+) mice). These results suggest that ASIC2 contributes to transduction of the renal myogenic response and are consistent with the protective role of myogenic constriction against renal injury and hypertension.

Keywords: acid-sensing ion channel 2; degenerin; pressure-induced constriction; renal injury.

Fig. 1.

Acid-sensing ion channel 2 (ASIC2) message and protein expression in the renal vasculature in ASIC2 mice. A: RT-PCR detection of ASIC2 and GAPDH message in dissected renal vessels. RT, reverse transcriptase. B: representative images of ASIC2 localization in enzymatically dispersed renal vascular smooth muscle cells (VSMCs) and semiquantitative analysis of ASIC2 labeling in VSMCs from ASIC2^+/+ and ASIC2^−/− mice. Data are means ± SE; n = 20 VSMCs/group obtained from 2 animals. C: ASIC2 localization in a renal arteriole labeled with an ASIC2 antibody directed to the COOH-terminus (ASIC2_cterm). *Significantly different from ASIC2^+/+ mice using a two-tail test at the P value indicated. L, vessel lumen; Cb, VSMC cell body.

Fig. 2.

Agonist-induced constriction in renal interlobar arteries from ASIC2 mice. Vasoconstrictor responses to the depolarizing agent KCl (A) and α-adrenergic agonist phenylephrine (PE; B) were similar in ASIC2^+/+ (solid diamonds, n = 6), ASIC2^+/− (shaded squares, n = 7) and ASIC2^−/− (open triangles, n = 8) mice. Data are means ± SE.

Fig. 3.

Myogenic constriction in renal interlobar arteries from ASIC2 mice. A: inner diameter responses to step increases in intraluminal pressure under Ca²⁺-containing (+Ca²⁺, solid line) and Ca²⁺-free (−Ca²⁺, dashed line) conditions in ASIC2^+/+ (solid diamonds, n = 6; left), ASIC2^+/− (shaded squares, n = 7; middle), and ASIC2^−/− (open diamonds, n = 8; right) mice. B: calculated myogenic tone (in %) increases with increasing intraluminal pressure in ASIC2^+/+ but not ASIC2^+/− or ASIC2^−/− artery segments. C: mean slope of the intraluminal pressure versus myogenic tone (in %) relationship in B. Morphological characteristics and baseline parameters are shown in Table 1. Data are means ± SE. *Significantly different compared with ASIC2^+/+ mice at a given pressure step (P < 0.05); ‡significantly different compared with ASIC2^−/− mice at a given pressure step (P < 0.05).

Fig. 4.

Renal blood flow (RBF) and renal vascular resistance (RVR) correction after a step increase in mean arterial pressure (MAP). A–F: time course of the response of MAP (A and D), RBF (B and E), and RVR (C and F) in ASIC2 mice to a step increase in MAP in ASIC2^+/+ (solid diamonds, n = 9), ASIC2^+/− (shaded squares, n = 7), and ASIC2^−/− (open triangles, n = 11) mice. The time course shows the responses 15 s before and 20 s after the step increase in pressure (time 0). Absolute values are shown in A–C, whereas values normalized to baseline (%baseline) are shown in D–F. KW, kidney weight; RU, resistance units. G–I: changes in MAP (G), RBF (H), and RVR (I) at the time period indicated from baseline. Morphological characteristics and baseline hemodynamic parameters are shown in Table 2. Data are means ± SE. *Significantly different compared with ASIC2^+/+ mice (P < 0.05).

Fig. 5.

Myogenic regulation of RBF after a step increase in MAP. A: the slope of the linear regression of RVR from time = 0–5 s, the time period in which the myogenic response is active, was used to determine the speed of myogenic RBF mechanisms in ASIC2^+/+ (solid diamonds, n = 9), ASIC2^+/− (shaded squares, n = 7), and ASIC2^−/− (open triangles, n = 11) animals. B: group data. Data are means ± SE. *Significantly different compared with ASIC2^+/+ mice (P < 0.05); ‡significantly different compared with ASIC2^−/− mice (P < 0.05).

Fig. 6.

Evidence of mild renal injury associated with loss of ASIC2. A–D: Western blot analysis of inflammatory markers transforming growth factor (TGF)-β (A) and target of antiproliferative antibody (TAPA)-1 (B) and injury markers collagen type III (C) and nephrin (D) from isolated glomeruli suggesting mild renal injury in mice lacking ASIC2. *Significantly different between the indicated groups (P < 0.05).